Hypospadias, cryptorchidism and breast cancer in children born to New Zealand servicemen who served in Malaya and may have had exposure to dibutyl phthalate: review of a previous study and updated review of international literature
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In 2012, it was reported that the children of male New Zealand soldiers who served in Malaya between 1948 and 1960 and used dibutyl phthalate (DBP) on their clothing showed increased risks of hypospadias, cryptorchidism, and breast cancer.[[1]] This was claimed to be the first report of a multigenerational development effect of DBP exposure in men. Since then, a great deal of research has been done on the effect of DBP and related chemicals, and New Zealand veterans still have concerns about the topic, so an updated review may be useful.
The New Zealand study
New Zealand soldiers serving in the “Emergency” in Malaya in 1948–1960 painted the seams of their uniforms, made of cotton, with a liquid containing dibutyl phthalate (DBP) to prevent them being bitten by trombiculid mites (chiggers, e.g., Eutrombicula hirsti), which carry the scrub typhus pathogen (Orientia tsutsugamushi).[[1]] In the New Zealand study,[[1]] the authors sent questionnaires to 252 New Zealand army veterans who had served in Malaya. They were asked whether they or their children or grandchildren suffered from any of eight conditions: cryptorchidism, defects of the penis (respondents were asked to specify, e.g., hypospadias), precocious puberty (female offspring only), low sperm count, reduced fertility, disorders of the ovary or uterus, and breast cancer.
The results were reported as showing significant increased risks of cryptorchidism and of hypospadias in male children, and of breast cancer in females. Thus, the study showed something never reported before: that a time-limited exposure to DBP in adult men could result in effects to their children, both male and female, born at various times after that exposure ceased. The authors claimed the study to be the first report of a multigenerational developmental effect following DBP exposure in human males.[[1]] They hypothesised that this was due to an effect on sperm, possibly by epigenetic gene regulation. These dramatic results and interpretations, if correct, would be of worldwide biological importance, and require that the evidence underlying them is rigorous and valid.
Methods
The New Zealand study was reassessed, and published comments and citations of the study were identified and reviewed.
For the literature review, the extensive review by the US Environmental Protection Agency on male and female reproductive effects of phthalates[[2]] was accepted as reviewing literature published up to January 2017, and the systematic review by Liu et al.[[3]] was accepted as reviewing literature on phthalates and breast cancer published up to November 2020. More recent literature was searched for on Medline from January 2017 to November 2022, for human studies indexed as phthalate and hypospadias, cryptorchidism, testis, or breast cancer; 85 papers were identified, from which 17 new studies and 11 reviews were assessed in detail. The other studies had been already included in the major reviews or were of mechanisms or experimental studies. This is not a comprehensive systematic review, and only the relevant studies are discussed in this paper.
Critique of the New Zealand study
The evidence presented in the 2012 paper is from a weak epidemiological study which was incorrectly analysed. The study was based on questionnaires sent in 2010 to 252 New Zealand army veterans whose military records showed that they had served in the Malayan emergency between 1948–1960, and who were members of the Canterbury branch of the Malaysian Veterans Association. Only 85 subjects (34%) responded, of whom 13 reported that they had not used DBP and were excluded from the analysis. One other was excluded with no reason given, leaving 71 veterans, of whom 58 reported having children, all born after their fathers returned to New Zealand. There were 155 children (79 male, 76 female).
In the 79 male children, two cases of hypospadias (2.5%) and four cases of cryptorchidism (5.1%) were reported (Table 1). These were compared to expected rates of 0.3% and 1% respectively, thus showing substantial excesses. However, the comparison results are incorrect, perhaps being based on total populations rather than males.[[4]] The expected frequencies in New Zealand male births can be only approximate, as the years of birth of the cases are not given, but are about 0.65% for hypospadias and 1.8% for cryptorchidism.[[4]] The correct comparisons still show an excess, but close to the margin of statistical significance at the 5% level[[4]] (Table 1). However, the main issue is that veterans who know about these conditions in their children would be more motivated to respond to the questionnaire. With only a 35% response to a questionnaire that specifically indicated these diseases as topics of interest, the result based only on the respondents is very likely to over-estimate the rate in all veterans sent the survey.[[5]] There was only a very limited validation of the disease reported. Thus, the study should have reported, at the most, that an apparent excess of these conditions was reported by the respondents, but this could be due to selective response.
Amongst the 76 females, there were three cases of breast cancer reported (4.0%). This was compared to a 0.48%, which is the annual incidence of breast cancer in a US source.[[4]] However, three cases are the number which occurred up to the time of the survey and needs to be compared with the cumulative incidence of breast cancer expected up to the ages attained at the time of the survey. As these ages are not given, an exact comparison cannot be made. The cumulative risk of breast cancer in the general population in New Zealand reaches 4% at age 50 to 55[[4]], so the finding of three cases is similar to expectations.
The paper also had estimates of the effects of the estimated absorbed dose of DBP, but these were criticised as they were based on studies of rats,[[5]] while absorption of DBP across rat skin can be up to 130 times greater than across human tissue.[[6]]
Given the dramatic claim of this being the first study to show an intergenerational effect, it might be expected to gain worldwide attention. The paper has not been discussed in any other publication, apart from the two critical assessments. It has been cited in one paper with the comment that it was “based on a very small cohort,”[[7]] and the paper was identified for the major review discussed later,[[2,8]] but not included as the exposure information was based on self-report. Of more concern is that five other papers report the findings as factual without further comment.[[9–13]]
Thus, in considering the evidence that DBP could be associated with hypospadias, cryptorchidism, or breast cancer in the children of men exposed, the New Zealand study shows only weakly suggestive evidence of associations, which are likely to result from selective reporting.
Phthalates and health effects
Phthalic acid diesters (phthalates) are a class of manmade and multifunction chemicals used in many consumer and industrial products; for example, as plasticisers in polyvinyl chloride plastics, excipients in some medications, and scent retainers in some personal care products.[[14]] Human exposure is ubiquitous across the lifespan. Routes of exposure include exposure in utero through maternal exposures, ingestion, inhalation, and absorption through the skin.[[14]] After exposure, phthalate diesters are rapidly metabolised to monoester metabolites and excreted in the urine.
A detailed review of many health effects of phthalate exposure has been performed by the US Environmental Protection Agency in the United States, resulting in a series of papers published in 2018 and later.[[2]] This is a very detailed review, using internationally accepted methods, and therefore represents the best assessment of scientific literature up to that time. Scientific studies published up to January 2017 were assessed. For male reproductive effects, 5,651 publications were identified, 445 were assessed in detail, and 100 regarded as relevant and included in the published review.[[2]]
The group of phthalates encompasses a variety of compounds with different structures, properties, and use. The six phthalates assessed in the EPA review are: dibutyl phthalate (DBP) (the compound used in the New Zealand Vietnam veterans’ studies), di(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), di-isobutyl phthalate (DIBP), butyl benzyl phthalate (BBP), and diethyl phthalate (DEP). Of these, all except DEP can produce the “phthalate syndrome” of male reproductive effects in rats,[[15]] which includes cryptorchidism, hypospadias, other reproductive tract malformations, infertility, and decreased sperm count.
Phthalates, hypospadias, and cryptorchidism: literature review
Associations with maternal exposures in pregnancy
The most direct studies of reproductive effects of phthalates, as reviewed by the EPA, relate to maternal exposure during the relevant pregnancy, assessed by phthalates measured in the urine of the mothers at that time.[[2]] This accords with the mechanism accepted, that phthalates act as endocrine disruptors and have an anti-androgen effect during fetal development. It is distinct from a mutagenic effect, which would affect DNA and subsequent pregnancies.
The EPA review[[2]] identified 14 epidemiological studies with results on hypospadias, cryptorchidism, or incomplete testicular descent. The only studies accepted as having adequate assessments of exposure were three studies based on measurements of phthalate metabolites from a urine sample from the mother during pregnancy,[[16–18]] and one study based on an amniotic fluid sample from the mother.[[19]]
Only two of the studies had results for dibutyl phthalate (DBP), relating to its metabolite mono-butyl phthalate (MBP) (Table 2). Chevrier et al.[[16]] in France used two cohorts of pregnant women with male babies in which a single urine sample was taken between six and 30 weeks of pregnancy. From these cohorts, 19 cases of hypospadias and 50 cases of undescended testis assessed at birth were identified, along with three matched controls per case. Risks were calculated by tertiles of measured phthalate metabolite, adjusted for gestational age at urine collection, residence area, and other variables. No significant associations were seen, with the odds ratios in the highest tertile being 0.19 (95% confidence interval, CI, 0.02–2.3) for hypospadias, and 0.67 (CI 0.2–1.9) for cryptorchidism.
In a small study, Sathyanarayana et al.[[17]] studied a group of 371 women in the United States with male births, with a single urine sample collected. There were three cases of hypospadias and five of undescended testis, so these eight cases were assessed together. The odds ratios in relationship to higher levels of DBP metabolite was not significant (OR 1.81, CI 0.24–13.8).
Both these studies were assessed as “medium” confidence in the EPA assessment. A further study by Swan,[[18]] regarded as having “low” confidence, assessed incomplete testicular descent assessed from 1–36 months after birth in relationship to urine collected during pregnancy, and showed no association with DBP. Overall, the EPA assessment of the associations of maternal DBP and hypospadias and/or cryptorchidism was “slight”.
These studies and one other[[19]] also assessed the other five phthalates considered by the EPA. The overall evidence was considered “indeterminate” or “slight” for these phthalates.
Paternal and maternal occupational exposures
To assess paternal exposures, a relevant study would measure phthalates in the urine of fathers, prior to the conception of the male children. No such study has ever been done.
Some studies assess long-term phthalate exposure, estimated in terms of occupation and the use of a job-exposure matrix linking occupational titles to likely phthalate exposures. There are two large studies of this nature.
In Denmark,[[20]] 45,341 male singleton births in the Danish National Birth Cohort in 1997–2009 were identified, with fathers’ phthalate data on 929 cases of cryptorchidism (2.2%), and 244 of hypospadias (0.6%). For paternal exposures to phthalates, there was an increased risk of hypospadias for “probable exposure,” although this was not statistically significant, relative risk (RR) 1.7 (CI 0.9–2.5). There was no association with possible exposure. There was no association with cryptorchidism, RR 1.1 (CI 0.6–1.6). There was a similar non-significant increase of hypospadias associated with maternal occupational probable exposure, RR 2.3 (0.9–3.7), and no association with cryptorchidism.
In Western Australia, 1,145 males with hypospadias born in 1980–2000 were compared to 2411 male controls.[[21]] No significant increased risk was seen with paternal exposure to phthalates (OR 1.16, 95% limits 0.93–1.46). The results for maternal exposure were similar.
In a smaller study in Nice, France, 102 males with cryptorchidism were identified in 6,246 male births (1.6%).[[22]] The authors concluded that phthalates could be a risk factor, whereas eating fruits daily seemed protective; however, there were only three cases and one control exposed, which gives a calculated odds ratio of OR 6.3, limits 0.6–60.1 (not given in the paper). The study is clearly too small to support valid conclusions.
Conclusions
An association between DBP exposure in males and hypospadias or cryptorchidism in children born subsequently seems highly unlikely. The detailed EPA review has assessed in detail a much more direct relationship between maternal phthalate exposure in the pregnancy and these effects on male children, with the conclusion that the association is unlikely.[[2]] One study shows a suggestive association of hypospadias, but not cryptorchidism, with paternal occupational exposure to phthalates, but this would reflect chronic long-term exposure applying at the time of conception. To produce this type of effect, with a time-limited exposure to DBP producing effects on male offspring born considerably later, would require a remarkable biological mechanism, such as an epigenetic mechanism. While such mechanisms have been suggested, and are supported by some animal studies, no such mechanism has been demonstrated in humans with respect to phthalates or other similar pollutants.[[23]]
The effect of phthalates would be expected to be short-term. Phthalates entering the body by any route are rapidly metabolised, and the metabolites excreted in the urine. The half-life of phthalates in the body is estimated at 3–18 hours.[[14]] There is no evidence of long-term accumulation in the body, or long-term persistence after the cessation of exposure.
Breast cancer
A detailed systematic review and meta-analysis was published by Liu et al. in March 2021.[[3]] This reviewed studies published on the associations between breast cancer and phthalates, and also bisphenol A, identified in three major databases: Pubmed, Web of Sciences, and Embase, from 1990 to November 2020. Two-thousand, three hundred and eighty-eight potentially relevant articles were identified, and 311 assessed in detail. From these, six studies with results on phthalates were identified.
The six studies were all case-control studies, based on urine samples from the breast cancer patients and controls, so the data applies to phthalate levels after the diagnosis of breast cancer. To interpret these in regard to the causes of breast cancer, we must assume that these measurements are a valid proxy for phthalate levels at the times relevant to the causation of the breast cancer, which is likely to be months or years before diagnosis.
Only three studies give results for the metabolites of DBP. All three give non-significant but negative associations, with relative risks of 0.66, 0.85 and 0.85. These are derived respectively from case-control studies in 75 women with breast cancer in Alaska,[[24]] 91 cases in the National Health and Nutrition Examination Survey (NHANES) in the United States,[[25]] and 233 breast cancer cases in northern Mexico.[[26]] The meta-analysis gives an overall non-significant odds ratio of 0.80, 95% confidence limits 0.55–1.15. For the other phthalates, significant negative associations were seen for two, and for all the other phthalates no significant associations were seen. Thus, this meta-analysis shows no evidence suggesting an increase of breast cancer related to phthalates, and some suggestive evidence of a possible decrease in risk.
There have been two other major studies, each using a measure of phthalate exposure which may be a better indicator of long-term exposure than a single urine sample.[[27]] An important cohort study in Denmark[[28]] assessed phthalates in drugs prescribed. In a nationwide cohort of 1.12 million women, prescriptions for drugs were linked from the national prescription registry, and phthalate content of the drugs assessed. The highest category of DBP exposure was associated with an increased risk of estrogen receptor positive breast cancer (relative risk 1.9, limits 1.1–3.5), based on 13 cases in this group. There was no dose–response relationship, the risk in the next highest group being 0.7, limits 0.4–1.2. There was no association with estrogen receptor negative breast cancer. There were no associations seen with other phthalates assessed. The authors comment that the restriction to estrogen receptor positive breast cancer is consistent with an estrogenic effect of DBP.
Within the Women’s Health Initiative cohort study in the United States, comparisons were made between 419 women with invasive breast cancer and 838 unaffected controls, using measures of phthalates in three urine samples per participant collected over 1–3 years before breast cancer diagnosis. Several phthalates were assessed, none showing any significant associations. For DBP metabolites, the odds ratio in the highest dose group was 1.35, limits 0.94–1.94, and was lower, 1.28, in estrogen positive cancers than an estrogen negative cancer (1.53). Although some increased risks were seen in subgroup analyses (for example, estrogen positive breast cancer diagnosed within three years of the last biomarker measurement), such subgroup results may well be due to chance variation.
Thus, the Danish cohort study of medications suggests a possible increased risk of breast cancer, despite the numerous studies showing no associations. But this is still assessing the most direct effect: ingestion of phthalates by the woman herself prior to breast cancer diagnosis. The more indirect hypothesis that exposure of fathers could increase risk of breast cancer in their daughters after many years has no empiric evidence to support it.
Conclusions
The essential conclusion from this review is that the report that hypospadias, cryptorchidism, and breast cancer are increased in the children of New Zealand Malaysian veterans who served in Malaya and were exposed to dibutyl phthalate from its use on clothing,[[1]] is based on a small and weak study with incorrect calculations of results. The study itself, when correctly analysed, shows no excess of breast cancer, and only small apparent increases in hypospadias and cryptorchidism based on two and four cases, respectively. These could be due to chance, and are very likely produced by selective reporting, as only 34% of the subjects approached responded to the questionnaire. This study should be dismissed as being of very poor quality and unlikely to be valid.
In the time since, extensive reviews of the human health effects of phthalates have been conducted, using studies worldwide relating to DBP and also to other phthalates. There is no consistent evidence of associations with breast cancer. There are many studies that have assessed hypospadias and cryptorchidism, most relating to phthalate exposure of the mother during pregnancy; these studies are inconclusive.[[2]] There has also been one large study of fathers’ occupations, showing no effect on cryptorchidism, but a small non-significant excess of hypospadias, which is also seen in regard to mothers’ occupation. However, the studies relate to long-term chronic exposure which would apply around the time of conception, and not to the situation in veterans with a time limited exposure. There is no scientific evidence that supports the concept of health effects in children being affected by previous exposures of the fathers to dibutyl phthalate or other phthalates.
If the study published in 2012 has created anxiety or misinformation for veterans and their families, this should be corrected. The Veterans’ Association should consider if it needs to give guidance to its members and others to show that concerns of these issues are inappropriate.
View Table 1.
Summary
Abstract
Aim
Method
Results
Conclusion
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
1) Carran M, Shaw IC. New Zealand Malayan war veterans’ exposure to dibutylphthalate is associated with an increased incidence of cryptorchidism, hypospadias and breast cancer in their children. N Z Med J. 2012 Jul 29; 125(1358):52-63.
2) Radke EG, Braun JM, Meeker JD, Cooper GS. Phthalate exposure and male reproductive outcomes: A systematic review of the human epidemiological evidence. Environ Int. 2018 Dec;121(Pt 1):764-793. doi: 10.1016/j.envint.2018.07.029.
3) Liu G, Cai W, Liu H, Jiang H, Bi Y, Wang H. The Association of Bisphenol A and Phthalates with Risk of Breast Cancer: A Meta-Analysis. Int J Environ Res Public Health. 2021 Mar 1;18(5):2375. doi: 10.3390/ijerph18052375.
4) Elwood JM, Borman B. Increases in disease in Malayan war veterans’ children may be misleading. N Z Med J. 2012 Dec 14;125(1367):145-6.
5) McBride D, Schep L. Comment on Carran and Shaw’s “New Zealand Malayan war veterans’ exposure to dibutylphthalate” article. N Z Med J. 2012 Sep 7;125(1361):105-6.
6) Lehmann KP, Phillips S, Sar M, Foster PM, Gaido KW. Dose-dependent alterations in gene expression and testosterone synthesis in the fetal testes of male rats exposed to di (n-butyl) phthalate. Toxicol Sci. 2004 Sep; 81(1):60-8. doi: 10.1093/toxsci/kfh169.
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12) Braun JM, Messerlian C, Hauser R. Fathers Matter: Why It’s Time to Consider the Impact of Paternal Environmental Exposures on Children’s Health. Curr Epidemiol Rep. 2017 Mar;4(1):46-55. doi: 10.1007/s40471-017-0098-8.
13) Hsu YL, Hsieh CJ, Tsai EM, Hung JY, Chang WA, Hou MF et al. Didymin reverses phthalate ester-associated breast cancer aggravation in the breast cancer tumor microenvironment. Oncol Lett. 2016 Feb;11(2):1035-1042. oi: 10.3892/ol.2015.4008.
14) Johns LE, Cooper GS, Galizia A, Meeker JD. Exposure assessment issues in epidemiology studies of phthalates. Environ Int. 2015 Dec;85:27-39. doi: 10.1016/j.envint.2015.08.005.
15) National Research Council (US) Committee on the Health Risks of Phthalates. Phthalates and Cumulative Risk Assessment: The Tasks Ahead. Washington (DC): National Academies Press (US); 2008.
16) Chevrier C, Petit C, Philippat C, Mortamais M, Slama R, Rouget F et al. Maternal urinary phthalates and phenols and male genital anomalies. Epidemiology. 2012 Mar;23(2):353-6. doi: 10.1097/EDE.0b013e318246073e.
17) Sathyanarayana S, Grady R, Barrett ES, Redmon B, Nguyen RHN, Barthold JS et al. First trimester phthalate exposure and male newborn genital anomalies. Environ Res. 2016 Nov;151:777-782. doi: 10.1016/j.envres.2016.07.043.
18) Swan SH. Environmental phthalate exposure in relation to reproductive outcomes and other health endpoints in humans. Environ Res. 2008 Oct;108(2):177-84. doi: 10.1016/j.envres.2008.08.007.
19) Jensen MS, Anand-Ivell R, Nørgaard-Pedersen B, Jönsson BA, Bonde JP, Hougaard DM et al. Amniotic fluid phthalate levels and male fetal gonad function. Epidemiology. 2015 Jan;26(1):91-9. doi: 10.1097/EDE.0000000000000198.
20) Morales-Suárez-Varela MM, Toft GV, Jensen MS, Ramlau-Hansen C, Kaerlev L, Thulstrup AM et al. Parental occupational exposure to endocrine disrupting chemicals and male genital malformations: a study in the Danish National Birth Cohort study. Environ Health. 2011 Jan 14;10(1):3. doi: 10.1186/1476-069X-10-3. PMID: 21235764; PMCID: PMC3033238.
21) Nassar N, Abeywardana P, Barker A, Bower C. Parental occupational exposure to potential endocrine disrupting chemicals and risk of hypospadias in infants. Occup Environ Med. 2010 Sep;67(9):585-9. doi: 10.1136/oem.2009.048272.
22) Wagner-Mahler K, Kurzenne JY, Delattre I, Bérard E, Mas JC, Bornebush L et al. Prospective study on the prevalence and associated risk factors of cryptorchidism in 6246 newborn boys from Nice area, France. Int J Androl. 2011 Oct;34(5 Pt 2):e499-e510. doi: 10.1111/j.1365-2605.2011.01211.x.
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Hypospadias, cryptorchidism and breast cancer in children born to New Zealand servicemen who served in Malaya and may have had exposure to dibutyl phthalate: review of a previous study and updated review of international literature
View Article PDF
In 2012, it was reported that the children of male New Zealand soldiers who served in Malaya between 1948 and 1960 and used dibutyl phthalate (DBP) on their clothing showed increased risks of hypospadias, cryptorchidism, and breast cancer.[[1]] This was claimed to be the first report of a multigenerational development effect of DBP exposure in men. Since then, a great deal of research has been done on the effect of DBP and related chemicals, and New Zealand veterans still have concerns about the topic, so an updated review may be useful.
The New Zealand study
New Zealand soldiers serving in the “Emergency” in Malaya in 1948–1960 painted the seams of their uniforms, made of cotton, with a liquid containing dibutyl phthalate (DBP) to prevent them being bitten by trombiculid mites (chiggers, e.g., Eutrombicula hirsti), which carry the scrub typhus pathogen (Orientia tsutsugamushi).[[1]] In the New Zealand study,[[1]] the authors sent questionnaires to 252 New Zealand army veterans who had served in Malaya. They were asked whether they or their children or grandchildren suffered from any of eight conditions: cryptorchidism, defects of the penis (respondents were asked to specify, e.g., hypospadias), precocious puberty (female offspring only), low sperm count, reduced fertility, disorders of the ovary or uterus, and breast cancer.
The results were reported as showing significant increased risks of cryptorchidism and of hypospadias in male children, and of breast cancer in females. Thus, the study showed something never reported before: that a time-limited exposure to DBP in adult men could result in effects to their children, both male and female, born at various times after that exposure ceased. The authors claimed the study to be the first report of a multigenerational developmental effect following DBP exposure in human males.[[1]] They hypothesised that this was due to an effect on sperm, possibly by epigenetic gene regulation. These dramatic results and interpretations, if correct, would be of worldwide biological importance, and require that the evidence underlying them is rigorous and valid.
Methods
The New Zealand study was reassessed, and published comments and citations of the study were identified and reviewed.
For the literature review, the extensive review by the US Environmental Protection Agency on male and female reproductive effects of phthalates[[2]] was accepted as reviewing literature published up to January 2017, and the systematic review by Liu et al.[[3]] was accepted as reviewing literature on phthalates and breast cancer published up to November 2020. More recent literature was searched for on Medline from January 2017 to November 2022, for human studies indexed as phthalate and hypospadias, cryptorchidism, testis, or breast cancer; 85 papers were identified, from which 17 new studies and 11 reviews were assessed in detail. The other studies had been already included in the major reviews or were of mechanisms or experimental studies. This is not a comprehensive systematic review, and only the relevant studies are discussed in this paper.
Critique of the New Zealand study
The evidence presented in the 2012 paper is from a weak epidemiological study which was incorrectly analysed. The study was based on questionnaires sent in 2010 to 252 New Zealand army veterans whose military records showed that they had served in the Malayan emergency between 1948–1960, and who were members of the Canterbury branch of the Malaysian Veterans Association. Only 85 subjects (34%) responded, of whom 13 reported that they had not used DBP and were excluded from the analysis. One other was excluded with no reason given, leaving 71 veterans, of whom 58 reported having children, all born after their fathers returned to New Zealand. There were 155 children (79 male, 76 female).
In the 79 male children, two cases of hypospadias (2.5%) and four cases of cryptorchidism (5.1%) were reported (Table 1). These were compared to expected rates of 0.3% and 1% respectively, thus showing substantial excesses. However, the comparison results are incorrect, perhaps being based on total populations rather than males.[[4]] The expected frequencies in New Zealand male births can be only approximate, as the years of birth of the cases are not given, but are about 0.65% for hypospadias and 1.8% for cryptorchidism.[[4]] The correct comparisons still show an excess, but close to the margin of statistical significance at the 5% level[[4]] (Table 1). However, the main issue is that veterans who know about these conditions in their children would be more motivated to respond to the questionnaire. With only a 35% response to a questionnaire that specifically indicated these diseases as topics of interest, the result based only on the respondents is very likely to over-estimate the rate in all veterans sent the survey.[[5]] There was only a very limited validation of the disease reported. Thus, the study should have reported, at the most, that an apparent excess of these conditions was reported by the respondents, but this could be due to selective response.
Amongst the 76 females, there were three cases of breast cancer reported (4.0%). This was compared to a 0.48%, which is the annual incidence of breast cancer in a US source.[[4]] However, three cases are the number which occurred up to the time of the survey and needs to be compared with the cumulative incidence of breast cancer expected up to the ages attained at the time of the survey. As these ages are not given, an exact comparison cannot be made. The cumulative risk of breast cancer in the general population in New Zealand reaches 4% at age 50 to 55[[4]], so the finding of three cases is similar to expectations.
The paper also had estimates of the effects of the estimated absorbed dose of DBP, but these were criticised as they were based on studies of rats,[[5]] while absorption of DBP across rat skin can be up to 130 times greater than across human tissue.[[6]]
Given the dramatic claim of this being the first study to show an intergenerational effect, it might be expected to gain worldwide attention. The paper has not been discussed in any other publication, apart from the two critical assessments. It has been cited in one paper with the comment that it was “based on a very small cohort,”[[7]] and the paper was identified for the major review discussed later,[[2,8]] but not included as the exposure information was based on self-report. Of more concern is that five other papers report the findings as factual without further comment.[[9–13]]
Thus, in considering the evidence that DBP could be associated with hypospadias, cryptorchidism, or breast cancer in the children of men exposed, the New Zealand study shows only weakly suggestive evidence of associations, which are likely to result from selective reporting.
Phthalates and health effects
Phthalic acid diesters (phthalates) are a class of manmade and multifunction chemicals used in many consumer and industrial products; for example, as plasticisers in polyvinyl chloride plastics, excipients in some medications, and scent retainers in some personal care products.[[14]] Human exposure is ubiquitous across the lifespan. Routes of exposure include exposure in utero through maternal exposures, ingestion, inhalation, and absorption through the skin.[[14]] After exposure, phthalate diesters are rapidly metabolised to monoester metabolites and excreted in the urine.
A detailed review of many health effects of phthalate exposure has been performed by the US Environmental Protection Agency in the United States, resulting in a series of papers published in 2018 and later.[[2]] This is a very detailed review, using internationally accepted methods, and therefore represents the best assessment of scientific literature up to that time. Scientific studies published up to January 2017 were assessed. For male reproductive effects, 5,651 publications were identified, 445 were assessed in detail, and 100 regarded as relevant and included in the published review.[[2]]
The group of phthalates encompasses a variety of compounds with different structures, properties, and use. The six phthalates assessed in the EPA review are: dibutyl phthalate (DBP) (the compound used in the New Zealand Vietnam veterans’ studies), di(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), di-isobutyl phthalate (DIBP), butyl benzyl phthalate (BBP), and diethyl phthalate (DEP). Of these, all except DEP can produce the “phthalate syndrome” of male reproductive effects in rats,[[15]] which includes cryptorchidism, hypospadias, other reproductive tract malformations, infertility, and decreased sperm count.
Phthalates, hypospadias, and cryptorchidism: literature review
Associations with maternal exposures in pregnancy
The most direct studies of reproductive effects of phthalates, as reviewed by the EPA, relate to maternal exposure during the relevant pregnancy, assessed by phthalates measured in the urine of the mothers at that time.[[2]] This accords with the mechanism accepted, that phthalates act as endocrine disruptors and have an anti-androgen effect during fetal development. It is distinct from a mutagenic effect, which would affect DNA and subsequent pregnancies.
The EPA review[[2]] identified 14 epidemiological studies with results on hypospadias, cryptorchidism, or incomplete testicular descent. The only studies accepted as having adequate assessments of exposure were three studies based on measurements of phthalate metabolites from a urine sample from the mother during pregnancy,[[16–18]] and one study based on an amniotic fluid sample from the mother.[[19]]
Only two of the studies had results for dibutyl phthalate (DBP), relating to its metabolite mono-butyl phthalate (MBP) (Table 2). Chevrier et al.[[16]] in France used two cohorts of pregnant women with male babies in which a single urine sample was taken between six and 30 weeks of pregnancy. From these cohorts, 19 cases of hypospadias and 50 cases of undescended testis assessed at birth were identified, along with three matched controls per case. Risks were calculated by tertiles of measured phthalate metabolite, adjusted for gestational age at urine collection, residence area, and other variables. No significant associations were seen, with the odds ratios in the highest tertile being 0.19 (95% confidence interval, CI, 0.02–2.3) for hypospadias, and 0.67 (CI 0.2–1.9) for cryptorchidism.
In a small study, Sathyanarayana et al.[[17]] studied a group of 371 women in the United States with male births, with a single urine sample collected. There were three cases of hypospadias and five of undescended testis, so these eight cases were assessed together. The odds ratios in relationship to higher levels of DBP metabolite was not significant (OR 1.81, CI 0.24–13.8).
Both these studies were assessed as “medium” confidence in the EPA assessment. A further study by Swan,[[18]] regarded as having “low” confidence, assessed incomplete testicular descent assessed from 1–36 months after birth in relationship to urine collected during pregnancy, and showed no association with DBP. Overall, the EPA assessment of the associations of maternal DBP and hypospadias and/or cryptorchidism was “slight”.
These studies and one other[[19]] also assessed the other five phthalates considered by the EPA. The overall evidence was considered “indeterminate” or “slight” for these phthalates.
Paternal and maternal occupational exposures
To assess paternal exposures, a relevant study would measure phthalates in the urine of fathers, prior to the conception of the male children. No such study has ever been done.
Some studies assess long-term phthalate exposure, estimated in terms of occupation and the use of a job-exposure matrix linking occupational titles to likely phthalate exposures. There are two large studies of this nature.
In Denmark,[[20]] 45,341 male singleton births in the Danish National Birth Cohort in 1997–2009 were identified, with fathers’ phthalate data on 929 cases of cryptorchidism (2.2%), and 244 of hypospadias (0.6%). For paternal exposures to phthalates, there was an increased risk of hypospadias for “probable exposure,” although this was not statistically significant, relative risk (RR) 1.7 (CI 0.9–2.5). There was no association with possible exposure. There was no association with cryptorchidism, RR 1.1 (CI 0.6–1.6). There was a similar non-significant increase of hypospadias associated with maternal occupational probable exposure, RR 2.3 (0.9–3.7), and no association with cryptorchidism.
In Western Australia, 1,145 males with hypospadias born in 1980–2000 were compared to 2411 male controls.[[21]] No significant increased risk was seen with paternal exposure to phthalates (OR 1.16, 95% limits 0.93–1.46). The results for maternal exposure were similar.
In a smaller study in Nice, France, 102 males with cryptorchidism were identified in 6,246 male births (1.6%).[[22]] The authors concluded that phthalates could be a risk factor, whereas eating fruits daily seemed protective; however, there were only three cases and one control exposed, which gives a calculated odds ratio of OR 6.3, limits 0.6–60.1 (not given in the paper). The study is clearly too small to support valid conclusions.
Conclusions
An association between DBP exposure in males and hypospadias or cryptorchidism in children born subsequently seems highly unlikely. The detailed EPA review has assessed in detail a much more direct relationship between maternal phthalate exposure in the pregnancy and these effects on male children, with the conclusion that the association is unlikely.[[2]] One study shows a suggestive association of hypospadias, but not cryptorchidism, with paternal occupational exposure to phthalates, but this would reflect chronic long-term exposure applying at the time of conception. To produce this type of effect, with a time-limited exposure to DBP producing effects on male offspring born considerably later, would require a remarkable biological mechanism, such as an epigenetic mechanism. While such mechanisms have been suggested, and are supported by some animal studies, no such mechanism has been demonstrated in humans with respect to phthalates or other similar pollutants.[[23]]
The effect of phthalates would be expected to be short-term. Phthalates entering the body by any route are rapidly metabolised, and the metabolites excreted in the urine. The half-life of phthalates in the body is estimated at 3–18 hours.[[14]] There is no evidence of long-term accumulation in the body, or long-term persistence after the cessation of exposure.
Breast cancer
A detailed systematic review and meta-analysis was published by Liu et al. in March 2021.[[3]] This reviewed studies published on the associations between breast cancer and phthalates, and also bisphenol A, identified in three major databases: Pubmed, Web of Sciences, and Embase, from 1990 to November 2020. Two-thousand, three hundred and eighty-eight potentially relevant articles were identified, and 311 assessed in detail. From these, six studies with results on phthalates were identified.
The six studies were all case-control studies, based on urine samples from the breast cancer patients and controls, so the data applies to phthalate levels after the diagnosis of breast cancer. To interpret these in regard to the causes of breast cancer, we must assume that these measurements are a valid proxy for phthalate levels at the times relevant to the causation of the breast cancer, which is likely to be months or years before diagnosis.
Only three studies give results for the metabolites of DBP. All three give non-significant but negative associations, with relative risks of 0.66, 0.85 and 0.85. These are derived respectively from case-control studies in 75 women with breast cancer in Alaska,[[24]] 91 cases in the National Health and Nutrition Examination Survey (NHANES) in the United States,[[25]] and 233 breast cancer cases in northern Mexico.[[26]] The meta-analysis gives an overall non-significant odds ratio of 0.80, 95% confidence limits 0.55–1.15. For the other phthalates, significant negative associations were seen for two, and for all the other phthalates no significant associations were seen. Thus, this meta-analysis shows no evidence suggesting an increase of breast cancer related to phthalates, and some suggestive evidence of a possible decrease in risk.
There have been two other major studies, each using a measure of phthalate exposure which may be a better indicator of long-term exposure than a single urine sample.[[27]] An important cohort study in Denmark[[28]] assessed phthalates in drugs prescribed. In a nationwide cohort of 1.12 million women, prescriptions for drugs were linked from the national prescription registry, and phthalate content of the drugs assessed. The highest category of DBP exposure was associated with an increased risk of estrogen receptor positive breast cancer (relative risk 1.9, limits 1.1–3.5), based on 13 cases in this group. There was no dose–response relationship, the risk in the next highest group being 0.7, limits 0.4–1.2. There was no association with estrogen receptor negative breast cancer. There were no associations seen with other phthalates assessed. The authors comment that the restriction to estrogen receptor positive breast cancer is consistent with an estrogenic effect of DBP.
Within the Women’s Health Initiative cohort study in the United States, comparisons were made between 419 women with invasive breast cancer and 838 unaffected controls, using measures of phthalates in three urine samples per participant collected over 1–3 years before breast cancer diagnosis. Several phthalates were assessed, none showing any significant associations. For DBP metabolites, the odds ratio in the highest dose group was 1.35, limits 0.94–1.94, and was lower, 1.28, in estrogen positive cancers than an estrogen negative cancer (1.53). Although some increased risks were seen in subgroup analyses (for example, estrogen positive breast cancer diagnosed within three years of the last biomarker measurement), such subgroup results may well be due to chance variation.
Thus, the Danish cohort study of medications suggests a possible increased risk of breast cancer, despite the numerous studies showing no associations. But this is still assessing the most direct effect: ingestion of phthalates by the woman herself prior to breast cancer diagnosis. The more indirect hypothesis that exposure of fathers could increase risk of breast cancer in their daughters after many years has no empiric evidence to support it.
Conclusions
The essential conclusion from this review is that the report that hypospadias, cryptorchidism, and breast cancer are increased in the children of New Zealand Malaysian veterans who served in Malaya and were exposed to dibutyl phthalate from its use on clothing,[[1]] is based on a small and weak study with incorrect calculations of results. The study itself, when correctly analysed, shows no excess of breast cancer, and only small apparent increases in hypospadias and cryptorchidism based on two and four cases, respectively. These could be due to chance, and are very likely produced by selective reporting, as only 34% of the subjects approached responded to the questionnaire. This study should be dismissed as being of very poor quality and unlikely to be valid.
In the time since, extensive reviews of the human health effects of phthalates have been conducted, using studies worldwide relating to DBP and also to other phthalates. There is no consistent evidence of associations with breast cancer. There are many studies that have assessed hypospadias and cryptorchidism, most relating to phthalate exposure of the mother during pregnancy; these studies are inconclusive.[[2]] There has also been one large study of fathers’ occupations, showing no effect on cryptorchidism, but a small non-significant excess of hypospadias, which is also seen in regard to mothers’ occupation. However, the studies relate to long-term chronic exposure which would apply around the time of conception, and not to the situation in veterans with a time limited exposure. There is no scientific evidence that supports the concept of health effects in children being affected by previous exposures of the fathers to dibutyl phthalate or other phthalates.
If the study published in 2012 has created anxiety or misinformation for veterans and their families, this should be corrected. The Veterans’ Association should consider if it needs to give guidance to its members and others to show that concerns of these issues are inappropriate.
View Table 1.
Summary
Abstract
Aim
Method
Results
Conclusion
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
1) Carran M, Shaw IC. New Zealand Malayan war veterans’ exposure to dibutylphthalate is associated with an increased incidence of cryptorchidism, hypospadias and breast cancer in their children. N Z Med J. 2012 Jul 29; 125(1358):52-63.
2) Radke EG, Braun JM, Meeker JD, Cooper GS. Phthalate exposure and male reproductive outcomes: A systematic review of the human epidemiological evidence. Environ Int. 2018 Dec;121(Pt 1):764-793. doi: 10.1016/j.envint.2018.07.029.
3) Liu G, Cai W, Liu H, Jiang H, Bi Y, Wang H. The Association of Bisphenol A and Phthalates with Risk of Breast Cancer: A Meta-Analysis. Int J Environ Res Public Health. 2021 Mar 1;18(5):2375. doi: 10.3390/ijerph18052375.
4) Elwood JM, Borman B. Increases in disease in Malayan war veterans’ children may be misleading. N Z Med J. 2012 Dec 14;125(1367):145-6.
5) McBride D, Schep L. Comment on Carran and Shaw’s “New Zealand Malayan war veterans’ exposure to dibutylphthalate” article. N Z Med J. 2012 Sep 7;125(1361):105-6.
6) Lehmann KP, Phillips S, Sar M, Foster PM, Gaido KW. Dose-dependent alterations in gene expression and testosterone synthesis in the fetal testes of male rats exposed to di (n-butyl) phthalate. Toxicol Sci. 2004 Sep; 81(1):60-8. doi: 10.1093/toxsci/kfh169.
7) Gurney JK, McGlynn KA, Stanley J, Merriman T, Signal V, Shaw C et al. Risk factors for cryptorchidism. Nat Rev Urol. 2017 Sep;14(9):534-548. doi: 10.1038/nrurol.2017.90.
8) Radke EG, Glenn BS, Braun JM, Cooper GS. Phthalate exposure and female reproductive and developmental outcomes: a systematic review of the human epidemiological evidence. Environ Int. 2019 Sep;130:104580. doi: 10.1016/j.envint.2019.02.003.
9) Batra V, Norman E, Morgan HL, Watkins AJ. Parental Programming of Offspring Health: The Intricate Interplay between Diet, Environment, Reproduction and Development. Biomolecules. 2022 Sep 13;12(9):1289. doi: 10.3390/biom12091289.
10) Nicolella HD, de Assis S. Epigenetic Inheritance: Intergenerational Effects of Pesticides and Other Endocrine Disruptors on Cancer Development. Int J Mol Sci. 2022 Apr 23;23(9):4671. doi: 10.3390/ijms23094671.
11) da Cruz RS, Chen E, Smith M, Bates J, de Assis S. Diet and Transgenerational Epigenetic Inheritance of Breast Cancer: The Role of the Paternal Germline. Front Nutr. 2020 Jul 15;7:93. doi: 10.3389/fnut.2020.00093.
12) Braun JM, Messerlian C, Hauser R. Fathers Matter: Why It’s Time to Consider the Impact of Paternal Environmental Exposures on Children’s Health. Curr Epidemiol Rep. 2017 Mar;4(1):46-55. doi: 10.1007/s40471-017-0098-8.
13) Hsu YL, Hsieh CJ, Tsai EM, Hung JY, Chang WA, Hou MF et al. Didymin reverses phthalate ester-associated breast cancer aggravation in the breast cancer tumor microenvironment. Oncol Lett. 2016 Feb;11(2):1035-1042. oi: 10.3892/ol.2015.4008.
14) Johns LE, Cooper GS, Galizia A, Meeker JD. Exposure assessment issues in epidemiology studies of phthalates. Environ Int. 2015 Dec;85:27-39. doi: 10.1016/j.envint.2015.08.005.
15) National Research Council (US) Committee on the Health Risks of Phthalates. Phthalates and Cumulative Risk Assessment: The Tasks Ahead. Washington (DC): National Academies Press (US); 2008.
16) Chevrier C, Petit C, Philippat C, Mortamais M, Slama R, Rouget F et al. Maternal urinary phthalates and phenols and male genital anomalies. Epidemiology. 2012 Mar;23(2):353-6. doi: 10.1097/EDE.0b013e318246073e.
17) Sathyanarayana S, Grady R, Barrett ES, Redmon B, Nguyen RHN, Barthold JS et al. First trimester phthalate exposure and male newborn genital anomalies. Environ Res. 2016 Nov;151:777-782. doi: 10.1016/j.envres.2016.07.043.
18) Swan SH. Environmental phthalate exposure in relation to reproductive outcomes and other health endpoints in humans. Environ Res. 2008 Oct;108(2):177-84. doi: 10.1016/j.envres.2008.08.007.
19) Jensen MS, Anand-Ivell R, Nørgaard-Pedersen B, Jönsson BA, Bonde JP, Hougaard DM et al. Amniotic fluid phthalate levels and male fetal gonad function. Epidemiology. 2015 Jan;26(1):91-9. doi: 10.1097/EDE.0000000000000198.
20) Morales-Suárez-Varela MM, Toft GV, Jensen MS, Ramlau-Hansen C, Kaerlev L, Thulstrup AM et al. Parental occupational exposure to endocrine disrupting chemicals and male genital malformations: a study in the Danish National Birth Cohort study. Environ Health. 2011 Jan 14;10(1):3. doi: 10.1186/1476-069X-10-3. PMID: 21235764; PMCID: PMC3033238.
21) Nassar N, Abeywardana P, Barker A, Bower C. Parental occupational exposure to potential endocrine disrupting chemicals and risk of hypospadias in infants. Occup Environ Med. 2010 Sep;67(9):585-9. doi: 10.1136/oem.2009.048272.
22) Wagner-Mahler K, Kurzenne JY, Delattre I, Bérard E, Mas JC, Bornebush L et al. Prospective study on the prevalence and associated risk factors of cryptorchidism in 6246 newborn boys from Nice area, France. Int J Androl. 2011 Oct;34(5 Pt 2):e499-e510. doi: 10.1111/j.1365-2605.2011.01211.x.
23) Skinner MK, Manikkam M, Guerrero-Bosagna C. Epigenetic transgenerational actions of environmental factors in disease etiology. Trends Endocrinol Metab. 2010 Apr;21(4):214-22. doi: 10.1016/j.tem.2009.12.007.
24) Holmes AK, Koller KR, Kieszak SM, Sjodin A, Calafat AM, Sacco FD et al. Case-control study of breast cancer and exposure to synthetic environmental chemicals among Alaska Native women. Int J Circumpolar Health. 2014 Nov 13;73(1):25760. doi: 10.3402/ijch.v73.25760.
25) Morgan M, Deoraj A, Felty Q, Roy D. Environmental estrogen-like endocrine disrupting chemicals and breast cancer. Mol Cell Endocrinol. 2017 Dec 5;457:89-102. doi: 10.1016/j.mce.2016.10.003.
26) López-Carrillo L, Hernández-Ramírez RU, Calafat AM, Torres-Sánchez L, Galván-Portillo M, Needham LL et al. Exposure to phthalates and breast cancer risk in northern Mexico. Environ Health Perspect. 2010 Apr;118(4):539-44. doi: 10.1289/ehp.0901091.
27) Kantor ED, Romano ME. Phthalate Exposure From Prescription Medications and Breast Cancer Risk. J Clin Oncol. 2019 Jul 20;37(21):1775-1777. doi: 10.1200/JCO.19.01003.
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29) Altman DG, Machin D, Bryant T, Gardner M, editors. Statistics with confidence: Confidence intervals and statistical guidelines. 2nd ed. London: British Medical Journal; 2000.
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Hypospadias, cryptorchidism and breast cancer in children born to New Zealand servicemen who served in Malaya and may have had exposure to dibutyl phthalate: review of a previous study and updated review of international literature
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In 2012, it was reported that the children of male New Zealand soldiers who served in Malaya between 1948 and 1960 and used dibutyl phthalate (DBP) on their clothing showed increased risks of hypospadias, cryptorchidism, and breast cancer.[[1]] This was claimed to be the first report of a multigenerational development effect of DBP exposure in men. Since then, a great deal of research has been done on the effect of DBP and related chemicals, and New Zealand veterans still have concerns about the topic, so an updated review may be useful.
The New Zealand study
New Zealand soldiers serving in the “Emergency” in Malaya in 1948–1960 painted the seams of their uniforms, made of cotton, with a liquid containing dibutyl phthalate (DBP) to prevent them being bitten by trombiculid mites (chiggers, e.g., Eutrombicula hirsti), which carry the scrub typhus pathogen (Orientia tsutsugamushi).[[1]] In the New Zealand study,[[1]] the authors sent questionnaires to 252 New Zealand army veterans who had served in Malaya. They were asked whether they or their children or grandchildren suffered from any of eight conditions: cryptorchidism, defects of the penis (respondents were asked to specify, e.g., hypospadias), precocious puberty (female offspring only), low sperm count, reduced fertility, disorders of the ovary or uterus, and breast cancer.
The results were reported as showing significant increased risks of cryptorchidism and of hypospadias in male children, and of breast cancer in females. Thus, the study showed something never reported before: that a time-limited exposure to DBP in adult men could result in effects to their children, both male and female, born at various times after that exposure ceased. The authors claimed the study to be the first report of a multigenerational developmental effect following DBP exposure in human males.[[1]] They hypothesised that this was due to an effect on sperm, possibly by epigenetic gene regulation. These dramatic results and interpretations, if correct, would be of worldwide biological importance, and require that the evidence underlying them is rigorous and valid.
Methods
The New Zealand study was reassessed, and published comments and citations of the study were identified and reviewed.
For the literature review, the extensive review by the US Environmental Protection Agency on male and female reproductive effects of phthalates[[2]] was accepted as reviewing literature published up to January 2017, and the systematic review by Liu et al.[[3]] was accepted as reviewing literature on phthalates and breast cancer published up to November 2020. More recent literature was searched for on Medline from January 2017 to November 2022, for human studies indexed as phthalate and hypospadias, cryptorchidism, testis, or breast cancer; 85 papers were identified, from which 17 new studies and 11 reviews were assessed in detail. The other studies had been already included in the major reviews or were of mechanisms or experimental studies. This is not a comprehensive systematic review, and only the relevant studies are discussed in this paper.
Critique of the New Zealand study
The evidence presented in the 2012 paper is from a weak epidemiological study which was incorrectly analysed. The study was based on questionnaires sent in 2010 to 252 New Zealand army veterans whose military records showed that they had served in the Malayan emergency between 1948–1960, and who were members of the Canterbury branch of the Malaysian Veterans Association. Only 85 subjects (34%) responded, of whom 13 reported that they had not used DBP and were excluded from the analysis. One other was excluded with no reason given, leaving 71 veterans, of whom 58 reported having children, all born after their fathers returned to New Zealand. There were 155 children (79 male, 76 female).
In the 79 male children, two cases of hypospadias (2.5%) and four cases of cryptorchidism (5.1%) were reported (Table 1). These were compared to expected rates of 0.3% and 1% respectively, thus showing substantial excesses. However, the comparison results are incorrect, perhaps being based on total populations rather than males.[[4]] The expected frequencies in New Zealand male births can be only approximate, as the years of birth of the cases are not given, but are about 0.65% for hypospadias and 1.8% for cryptorchidism.[[4]] The correct comparisons still show an excess, but close to the margin of statistical significance at the 5% level[[4]] (Table 1). However, the main issue is that veterans who know about these conditions in their children would be more motivated to respond to the questionnaire. With only a 35% response to a questionnaire that specifically indicated these diseases as topics of interest, the result based only on the respondents is very likely to over-estimate the rate in all veterans sent the survey.[[5]] There was only a very limited validation of the disease reported. Thus, the study should have reported, at the most, that an apparent excess of these conditions was reported by the respondents, but this could be due to selective response.
Amongst the 76 females, there were three cases of breast cancer reported (4.0%). This was compared to a 0.48%, which is the annual incidence of breast cancer in a US source.[[4]] However, three cases are the number which occurred up to the time of the survey and needs to be compared with the cumulative incidence of breast cancer expected up to the ages attained at the time of the survey. As these ages are not given, an exact comparison cannot be made. The cumulative risk of breast cancer in the general population in New Zealand reaches 4% at age 50 to 55[[4]], so the finding of three cases is similar to expectations.
The paper also had estimates of the effects of the estimated absorbed dose of DBP, but these were criticised as they were based on studies of rats,[[5]] while absorption of DBP across rat skin can be up to 130 times greater than across human tissue.[[6]]
Given the dramatic claim of this being the first study to show an intergenerational effect, it might be expected to gain worldwide attention. The paper has not been discussed in any other publication, apart from the two critical assessments. It has been cited in one paper with the comment that it was “based on a very small cohort,”[[7]] and the paper was identified for the major review discussed later,[[2,8]] but not included as the exposure information was based on self-report. Of more concern is that five other papers report the findings as factual without further comment.[[9–13]]
Thus, in considering the evidence that DBP could be associated with hypospadias, cryptorchidism, or breast cancer in the children of men exposed, the New Zealand study shows only weakly suggestive evidence of associations, which are likely to result from selective reporting.
Phthalates and health effects
Phthalic acid diesters (phthalates) are a class of manmade and multifunction chemicals used in many consumer and industrial products; for example, as plasticisers in polyvinyl chloride plastics, excipients in some medications, and scent retainers in some personal care products.[[14]] Human exposure is ubiquitous across the lifespan. Routes of exposure include exposure in utero through maternal exposures, ingestion, inhalation, and absorption through the skin.[[14]] After exposure, phthalate diesters are rapidly metabolised to monoester metabolites and excreted in the urine.
A detailed review of many health effects of phthalate exposure has been performed by the US Environmental Protection Agency in the United States, resulting in a series of papers published in 2018 and later.[[2]] This is a very detailed review, using internationally accepted methods, and therefore represents the best assessment of scientific literature up to that time. Scientific studies published up to January 2017 were assessed. For male reproductive effects, 5,651 publications were identified, 445 were assessed in detail, and 100 regarded as relevant and included in the published review.[[2]]
The group of phthalates encompasses a variety of compounds with different structures, properties, and use. The six phthalates assessed in the EPA review are: dibutyl phthalate (DBP) (the compound used in the New Zealand Vietnam veterans’ studies), di(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), di-isobutyl phthalate (DIBP), butyl benzyl phthalate (BBP), and diethyl phthalate (DEP). Of these, all except DEP can produce the “phthalate syndrome” of male reproductive effects in rats,[[15]] which includes cryptorchidism, hypospadias, other reproductive tract malformations, infertility, and decreased sperm count.
Phthalates, hypospadias, and cryptorchidism: literature review
Associations with maternal exposures in pregnancy
The most direct studies of reproductive effects of phthalates, as reviewed by the EPA, relate to maternal exposure during the relevant pregnancy, assessed by phthalates measured in the urine of the mothers at that time.[[2]] This accords with the mechanism accepted, that phthalates act as endocrine disruptors and have an anti-androgen effect during fetal development. It is distinct from a mutagenic effect, which would affect DNA and subsequent pregnancies.
The EPA review[[2]] identified 14 epidemiological studies with results on hypospadias, cryptorchidism, or incomplete testicular descent. The only studies accepted as having adequate assessments of exposure were three studies based on measurements of phthalate metabolites from a urine sample from the mother during pregnancy,[[16–18]] and one study based on an amniotic fluid sample from the mother.[[19]]
Only two of the studies had results for dibutyl phthalate (DBP), relating to its metabolite mono-butyl phthalate (MBP) (Table 2). Chevrier et al.[[16]] in France used two cohorts of pregnant women with male babies in which a single urine sample was taken between six and 30 weeks of pregnancy. From these cohorts, 19 cases of hypospadias and 50 cases of undescended testis assessed at birth were identified, along with three matched controls per case. Risks were calculated by tertiles of measured phthalate metabolite, adjusted for gestational age at urine collection, residence area, and other variables. No significant associations were seen, with the odds ratios in the highest tertile being 0.19 (95% confidence interval, CI, 0.02–2.3) for hypospadias, and 0.67 (CI 0.2–1.9) for cryptorchidism.
In a small study, Sathyanarayana et al.[[17]] studied a group of 371 women in the United States with male births, with a single urine sample collected. There were three cases of hypospadias and five of undescended testis, so these eight cases were assessed together. The odds ratios in relationship to higher levels of DBP metabolite was not significant (OR 1.81, CI 0.24–13.8).
Both these studies were assessed as “medium” confidence in the EPA assessment. A further study by Swan,[[18]] regarded as having “low” confidence, assessed incomplete testicular descent assessed from 1–36 months after birth in relationship to urine collected during pregnancy, and showed no association with DBP. Overall, the EPA assessment of the associations of maternal DBP and hypospadias and/or cryptorchidism was “slight”.
These studies and one other[[19]] also assessed the other five phthalates considered by the EPA. The overall evidence was considered “indeterminate” or “slight” for these phthalates.
Paternal and maternal occupational exposures
To assess paternal exposures, a relevant study would measure phthalates in the urine of fathers, prior to the conception of the male children. No such study has ever been done.
Some studies assess long-term phthalate exposure, estimated in terms of occupation and the use of a job-exposure matrix linking occupational titles to likely phthalate exposures. There are two large studies of this nature.
In Denmark,[[20]] 45,341 male singleton births in the Danish National Birth Cohort in 1997–2009 were identified, with fathers’ phthalate data on 929 cases of cryptorchidism (2.2%), and 244 of hypospadias (0.6%). For paternal exposures to phthalates, there was an increased risk of hypospadias for “probable exposure,” although this was not statistically significant, relative risk (RR) 1.7 (CI 0.9–2.5). There was no association with possible exposure. There was no association with cryptorchidism, RR 1.1 (CI 0.6–1.6). There was a similar non-significant increase of hypospadias associated with maternal occupational probable exposure, RR 2.3 (0.9–3.7), and no association with cryptorchidism.
In Western Australia, 1,145 males with hypospadias born in 1980–2000 were compared to 2411 male controls.[[21]] No significant increased risk was seen with paternal exposure to phthalates (OR 1.16, 95% limits 0.93–1.46). The results for maternal exposure were similar.
In a smaller study in Nice, France, 102 males with cryptorchidism were identified in 6,246 male births (1.6%).[[22]] The authors concluded that phthalates could be a risk factor, whereas eating fruits daily seemed protective; however, there were only three cases and one control exposed, which gives a calculated odds ratio of OR 6.3, limits 0.6–60.1 (not given in the paper). The study is clearly too small to support valid conclusions.
Conclusions
An association between DBP exposure in males and hypospadias or cryptorchidism in children born subsequently seems highly unlikely. The detailed EPA review has assessed in detail a much more direct relationship between maternal phthalate exposure in the pregnancy and these effects on male children, with the conclusion that the association is unlikely.[[2]] One study shows a suggestive association of hypospadias, but not cryptorchidism, with paternal occupational exposure to phthalates, but this would reflect chronic long-term exposure applying at the time of conception. To produce this type of effect, with a time-limited exposure to DBP producing effects on male offspring born considerably later, would require a remarkable biological mechanism, such as an epigenetic mechanism. While such mechanisms have been suggested, and are supported by some animal studies, no such mechanism has been demonstrated in humans with respect to phthalates or other similar pollutants.[[23]]
The effect of phthalates would be expected to be short-term. Phthalates entering the body by any route are rapidly metabolised, and the metabolites excreted in the urine. The half-life of phthalates in the body is estimated at 3–18 hours.[[14]] There is no evidence of long-term accumulation in the body, or long-term persistence after the cessation of exposure.
Breast cancer
A detailed systematic review and meta-analysis was published by Liu et al. in March 2021.[[3]] This reviewed studies published on the associations between breast cancer and phthalates, and also bisphenol A, identified in three major databases: Pubmed, Web of Sciences, and Embase, from 1990 to November 2020. Two-thousand, three hundred and eighty-eight potentially relevant articles were identified, and 311 assessed in detail. From these, six studies with results on phthalates were identified.
The six studies were all case-control studies, based on urine samples from the breast cancer patients and controls, so the data applies to phthalate levels after the diagnosis of breast cancer. To interpret these in regard to the causes of breast cancer, we must assume that these measurements are a valid proxy for phthalate levels at the times relevant to the causation of the breast cancer, which is likely to be months or years before diagnosis.
Only three studies give results for the metabolites of DBP. All three give non-significant but negative associations, with relative risks of 0.66, 0.85 and 0.85. These are derived respectively from case-control studies in 75 women with breast cancer in Alaska,[[24]] 91 cases in the National Health and Nutrition Examination Survey (NHANES) in the United States,[[25]] and 233 breast cancer cases in northern Mexico.[[26]] The meta-analysis gives an overall non-significant odds ratio of 0.80, 95% confidence limits 0.55–1.15. For the other phthalates, significant negative associations were seen for two, and for all the other phthalates no significant associations were seen. Thus, this meta-analysis shows no evidence suggesting an increase of breast cancer related to phthalates, and some suggestive evidence of a possible decrease in risk.
There have been two other major studies, each using a measure of phthalate exposure which may be a better indicator of long-term exposure than a single urine sample.[[27]] An important cohort study in Denmark[[28]] assessed phthalates in drugs prescribed. In a nationwide cohort of 1.12 million women, prescriptions for drugs were linked from the national prescription registry, and phthalate content of the drugs assessed. The highest category of DBP exposure was associated with an increased risk of estrogen receptor positive breast cancer (relative risk 1.9, limits 1.1–3.5), based on 13 cases in this group. There was no dose–response relationship, the risk in the next highest group being 0.7, limits 0.4–1.2. There was no association with estrogen receptor negative breast cancer. There were no associations seen with other phthalates assessed. The authors comment that the restriction to estrogen receptor positive breast cancer is consistent with an estrogenic effect of DBP.
Within the Women’s Health Initiative cohort study in the United States, comparisons were made between 419 women with invasive breast cancer and 838 unaffected controls, using measures of phthalates in three urine samples per participant collected over 1–3 years before breast cancer diagnosis. Several phthalates were assessed, none showing any significant associations. For DBP metabolites, the odds ratio in the highest dose group was 1.35, limits 0.94–1.94, and was lower, 1.28, in estrogen positive cancers than an estrogen negative cancer (1.53). Although some increased risks were seen in subgroup analyses (for example, estrogen positive breast cancer diagnosed within three years of the last biomarker measurement), such subgroup results may well be due to chance variation.
Thus, the Danish cohort study of medications suggests a possible increased risk of breast cancer, despite the numerous studies showing no associations. But this is still assessing the most direct effect: ingestion of phthalates by the woman herself prior to breast cancer diagnosis. The more indirect hypothesis that exposure of fathers could increase risk of breast cancer in their daughters after many years has no empiric evidence to support it.
Conclusions
The essential conclusion from this review is that the report that hypospadias, cryptorchidism, and breast cancer are increased in the children of New Zealand Malaysian veterans who served in Malaya and were exposed to dibutyl phthalate from its use on clothing,[[1]] is based on a small and weak study with incorrect calculations of results. The study itself, when correctly analysed, shows no excess of breast cancer, and only small apparent increases in hypospadias and cryptorchidism based on two and four cases, respectively. These could be due to chance, and are very likely produced by selective reporting, as only 34% of the subjects approached responded to the questionnaire. This study should be dismissed as being of very poor quality and unlikely to be valid.
In the time since, extensive reviews of the human health effects of phthalates have been conducted, using studies worldwide relating to DBP and also to other phthalates. There is no consistent evidence of associations with breast cancer. There are many studies that have assessed hypospadias and cryptorchidism, most relating to phthalate exposure of the mother during pregnancy; these studies are inconclusive.[[2]] There has also been one large study of fathers’ occupations, showing no effect on cryptorchidism, but a small non-significant excess of hypospadias, which is also seen in regard to mothers’ occupation. However, the studies relate to long-term chronic exposure which would apply around the time of conception, and not to the situation in veterans with a time limited exposure. There is no scientific evidence that supports the concept of health effects in children being affected by previous exposures of the fathers to dibutyl phthalate or other phthalates.
If the study published in 2012 has created anxiety or misinformation for veterans and their families, this should be corrected. The Veterans’ Association should consider if it needs to give guidance to its members and others to show that concerns of these issues are inappropriate.
View Table 1.
Summary
Abstract
Aim
Method
Results
Conclusion
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
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Hypospadias, cryptorchidism and breast cancer in children born to New Zealand servicemen who served in Malaya and may have had exposure to dibutyl phthalate: review of a previous study and updated review of international literature
New Zealand soldiers serving in the “Emergency” in Malaya in 1948–1960 painted the seams of their uniforms, made of cotton, with a liquid containing dibutyl phthalate (DBP) to prevent them being bitten by trombiculid mites (chiggers, e.g., Eutrombicula hirsti), which carry the scrub typhus pathogen (Orientia tsutsugamushi).
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