Journal of the New Zealand Medical Association, 02-June-2006, Vol 119 No 1235
Epidemiology of diabetes in New Zealand: revisit to a changing landscape
Grace Joshy, David Simmons
Almost a decade has passed since Simmons1,2 painted the portrait of diabetes epidemiology in New Zealand and warned about the increasing risk of diabetes and its complications, especially for Māori and Pacific peoples. When Moore and Lunt 3 re-examined the situation in 2000, they found the burden of diabetes and its complications escalating, especially end-stage renal failure (ESRF). They also noted the ageing population structure, increasing Pacific population (mostly of Samoan, Tongan, Niuean, and Cook Islands origin), and the obesity epidemic. Since this time, New Zealand’s population has continued to age (median age has increased 2.5 years over 10 years). Furthermore, it has grown by 6%, with a 40% increase in the Asian population (2001–2005).4 These figures point to an increasing Type 2 diabetes burden for New Zealand.
The New Zealand Ministry of Health has responded to the growing diabetes epidemic with a diabetes strategic plan5 in 1997, a Diabetes Implementation Plan6 in 2000, and a “Diabetes Toolkit”7 for district health boards (DHBs) in 2001. The latter included the establishment of Local Diabetes Teams at DHB level and the free annual Get Checked programme for diabetes patients. A set of guidelines for the management of Type 2 diabetes were released in 2003.8 A Ministry of Health/ Health Research Council grant was put out to tender in 2001 and again in 2003, which was subsequently awarded to the Te Wai o Rona: Diabetes Prevention Strategy team in the Waikato/Lakes districts.9
Results from a large number of important studies have been published since the last review, which have confirmed the picture of a disease increasing in numbers, especially at a younger age and consistent with a lowering of the age at onset of Type 2 diabetes.
The aim of this review is to describe the current burden of diabetes and the current district-based strategies underway to tackle a condition likely to impact on the ability of New Zealand to afford other health services.
A comprehensive review was undertaken using MEDLINE database, reviewing diabetes prevalence or complications studies/surveys reporting New Zealand-specific figures. Experimental intervention trials have been excluded. The Australia and New Zealand Dialysis and Transplant Registry (ANZDATA) Reports from 1990–2004, the MoH publications / reports, and New Zealand Society for Study of Diabetes conference abstract books from 2000 have been reviewed.
The latest unpublished results from the Get Checked programme, being the only national diabetes surveillance tool, were obtained from the MoH. The diabetes teams in all DHBs were consulted via email regarding current (unpublished) initiatives on diabetes control and prevention (10/21, 48% response). While a comprehensive attempt has been made to include current unpublished diabetes initiatives, there could be a limitation on the number of such initiatives included in this article due to the limited response.
As with many other countries,25 currently there are no up-to-date national diabetes prevalence data for New Zealand. The only area with comprehensive epidemiological data is South Auckland, where between 1991 and 1995 a household survey of 100,000 residents was undertaken26 with a nested study of those with undiagnosed diabetes undertaken thereafter.23
Table 1 shows the prevalence of diagnosed and undiagnosed diabetes in different population-based surveys by ethnic group. As no significant and consistent gender differences in prevalence have been found,27 prevalence data have been integrated.
Table 1. Prevalence (%) of known diabetes, undiagnosed diabetes, and IGT/IFG in New Zealand by ethnicity
* Age standardised; † Crude prevalence, Europeans include Asians, Māori include Polynesians; ‡ Asians include others; § Europeans include others; SADP=South Auckland Diabetes Project.
The SADP survey11 found a high prevalence of diabetes in the non-European populations of New Zealand (except in Chinese and Cambodians); the highest prevalence was found in South Asians—e.g. Asian Indians. (Figure 1). The prevalence of diabetes among Chinese was also low on the Middlemore Hospital surgical wards19 at this time and has been shown in other Chinese populations.28
The NZHS 2002/03 results showed an increased diabetes prevalence of 8.4% among Asians living in New Zealand when compared with 1996/7, although South Asians were also included in the Asian category.
Figure 1. Prevalence (%) of known (Type 1 and Type 2) diabetes among 40–49 year olds in South Auckland (by ethnic group)
Source: South Auckland Diabetes Project (SADP) survey, 1992–95.11 Middle East=e.g. Iranians, Iraqis, Egyptians; South Asians=e.g. Indians, Sri Lankans, Bangladeshi.
Compared with Europeans aged ≥40 years, the prevalence of undiagnosed diabetes is more than three-fold among Māori and more than four-fold among Pacific peoples.27 HbA1c screening of 50,819 subjects aged 20+ years found that Māori, Pacific people, and Indians had particularly high rates of elevated HbA1c.
The age-standardised proportion of individuals with HbA1c >6% in these ethnic groups were increased six-fold. Preliminary results from Te Wai o Rona Diabetes Prevention Strategy24 in the Waikato are consistent with the South Auckland data, but the age-specific prevalence of undiagnosed diabetes was greater than predicted in the younger age groups.
Risk factor screening is still recommended in New Zealand,29 although many of those with undiagnosed diabetes (25.0%) and dysglycaemia (31.4%) have no diabetes risk factors.30 Past studies have indicated the earlier onset of Type 2 diabetes in Māori (8–10 years earlier) and Pacific people (5–9 years earlier) than Europeans.31,32
The NZHS 1996/97 figures are in agreement with the results from the SADP survey regarding age at diabetes diagnosis among Europeans (50–55.5 years), Māori (41–43 years), and Pacific (45–47 years)—but the NZHS 2002/03 results for Māori and Pacific are contradictory (50 and 51 years respectively).
About 10–15% of diagnosed diabetes is Type 1 diabetes among European New Zealanders; it is approximately 5% among other ethnic groups. Of concern, the incidence of Type1 diabetes diagnosed before 20 years of age in Canterbury, New Zealand has increased 3.4-fold in 30 years—from 6.79 to 22.79 patients/100,000 per year starting from 1970.33 This increase is considered consistent with a worldwide increase in Type 1 diabetes.
In the most recent national study, Campbell-Stokes et al34 estimated the average annual incidence in 1999/2000 to be 17.9 per 100,000 (95% CI: 15.9–20.0) among children under 15 years. Unlike earlier studies, this study found that Māori, Pacific people, and Asians all had significantly lower incidence rates (both absolute and relative to their respective population proportions) than Europeans, although the basis of the ethnicity definition is not stated.
Although the prevalence of Type 1 diabetes was found to be lower in non-Europeans in a recent Christchurch study, they also noted the increasing number of Māori, Pacific, and Asian people with diabetes.20
Figure 2 shows the projected numbers with known diabetes by ethnic group across all surveys to date, although the cross comparisons are limited by the changing definitions of ethnicity and diabetes. Figure 2 also shows the different MOH diabetes forecasts for New Zealand (based upon the NZHS 96–97 and South Auckland Household Survey 91), which may be underestimates (e.g. the 2003 predictions were already less than the prevalence of diabetes among Europeans, Pacific peoples, and Māori males in the NZHS 2002/03 survey).
The age at onset of Type 2 diabetes has also been dropping, with increasing numbers of children and adolescents with Type 2 diabetes and women with Type 2 diabetes in pregnancy. The Auckland Diabetes Centre has reported increasing prevalence of Type 2 diabetes in adolescents.36 The prevalence of Type 2 diabetes among the adolescent clinic attendees was 1.8% in 1996, and 11.0% in 2002.
Northland Diabetes Service has reported that Type 2 diabetes presents before the age of 30 years in 2.66% of Māori diagnosed with diabetes.37 Among South Auckland women with gestational diabetes mellitus (GDM), a high proportion (4.3% European, 21% Māori, 21% Pacific) of Polynesians had permanent diabetes postnatally.38
A review of 1994/95 hospital records in South Auckland showed high rates of GDM in Māori and Pacific women who attended oral glucose challenge tests compared with Europeans 21. This study found that Pacific women were more likely to be screened (68.5%) when compared with Māori (47.3%) when both have high rates of GDM and Type 2 diabetes.
The prevalence of obesity in New Zealand has increased from 9.4% in 1977 to 19.9% in 2003 among males, and from 10.8% to 22.1% among females.39 Māori and Pacific people have a particularly high prevalence of obesity,23 physical inactivity,13 insulin resistance,13 and metabolic syndrome27 compared with Europeans (Table 2).
The association between body composition and central fat distribution with risk of diabetes appears to be independent of ethnicity40. While Asians appear to have comparatively lower obesity41, Rush et al42 have found high body fat composition for Asian Indians compared with Europeans for a given BMI.
Table 3 shows the risk factors for microvascular and macrovascular disease in the New Zealand studies to date. The poor glycaemic and lipid control among patients attending the clinic from 1992–9544 appears to have continued into this century. The Otago register has reported a mean HbA1c of 7.2% for Type 2 patients; 50.1% had HbA1c result >7% in 1998.45 The results of the Get Checked programme showed that 63% of Europeans, 27% of Māori, and 92% of Pacific people with diabetes had a free annual check in 2004 (personal communication, MoH). But the denominators are derived from the MOH forecast estimates and actual percentage of Pacific people getting free checks may be much lower. The 2004 results show poorer metabolic control (HbA1c > 8%), for Māori (40%) and Pacific people (51%) with compared with European/Other (23%).
Table 2. Prevalence of risk factors for diabetes and its complications
† European includes Other.
**The ATP III criteria for metabolic syndrome were considered to have been met when 3 or more of the following factors were present: waist circumference >102cm for men or >88cm for women, treated hypertension or systolic blood pressure (sBP) ≥130mmHg and/or diastolic blood pressure (dBP) ≥85mmHg as mean of two readings, triglycerides ≥1.7mmol/L, HDL <1.04mmol/L for men or <1.29mmol/L for women, fasting blood glucose (FBG) ≥6.1mmol/L, or diabetes.
‡ Obesity is body mass index (BMI) ≥30 for European/Other/Asian, BMI ≥32 for Māori/Pacific.
§ Asian includes Other.
Table 3. Clinical characteristics of diabetes patients
Data are mean ± SD unless otherwise stated; * Transferred from diet/pill to insulin; † Data are geometric mean.
NZHIS mortality data has attributed 3% of deaths in 2000 to diabetes.55 Difficulties in the coding of diabetes have been recognised for many years,49 yet continue to be rediscovered56 57 with 45%–55% under-coding especially among non-insulin using (Type 2) patients.
In spite of inadequate mortality statistics, the standardised mortality rate for diabetes mellitus during 1999 were 62.5 per 100,000 in Maori versus 11 in non-Maori 58. A 10-year follow-up of the predominantly European Type 2 diabetic cohort in Canterbury showed increased mortality (standardised mortality ratio 2.17), the cause of death being predominantly attributable to cardiovascular disease (CVD) (69.8%).59
The Canterbury insulin-treated Diabetic Registry has reported a CVD-related standardised mortality ratio of 4.48 for diagnosis age <30years and 2.05 for diagnosis age ≥30 years among those who commenced insulin within 12 months of diagnosis.60
The meta-analysis of studies from Asia Pacific region (including 10,326 subjects from New Zealand) revealed that the hazard ratio associated with diabetes was significantly higher for fatal cardiovascular disease (1.97), fatal coronary heart disease (2.19,) and fatal cerebrovascular disease (2.0).61
Table 4 shows the ethnic specific death rates from ESRD and ischaemic heart disease in the SADP cohort age 40–79 years.49 The standardised mortality ratio for renal failure is 8.37%, estimated from the Canterbury insulin-treated Diabetic Registry.60 This reflects the renal failure rate in insulin treated diabetes patients in a registry that has predominantly European patients (97.7%).
Very few reports relating to heart disease exist (Table 4). A review of records from Middlemore Hospital has reported significant ethnic differences in the prevalence of diabetes among in-patients aged 40+ with acute MI.52
Among the 449 new renal disease patients entering the ANZDATA registry in 2003,54 45% had diabetes (23% of European patients, 65% Maori, 67% Pacific, 50% Asian).
Diabetic nephropathy (40%) was the most common cause of end-stage renal disease (ESRD) in New Zealand, followed by glomerulonephritis (26%) and hypertension (10%). Type 2 diabetes (non-insulin and insulin requiring) was identified in 94% of diabetic nephropathic patients on the registry.
From the prospective data from ANZDATA reports, the numbers with of diabetes-related ESRD in Maori population are the highest, but appear to have reached equilibrium (Figure 3). The incidence of diabetes related ESRD in Europeans while lower than other ethnic groups, has also doubled since 1992. The crude prevalence of proteinuria and ESRD were higher in Maori and Pacific people compared with Europeans in the SADS survey62 in 1990 (Table 4).
Table 4. Diabetes-related mortality and complications
*Estimated from ANZDATA Registry 2001 and Census 2001; † Age and sex standardised; ‡ Age adjusted to total diabetes population; MI=Myocardial infarction.
A familial predisposition to renal disease was suggested from one study showing that the predisposition to diabetic nephropathy in Polynesians was associated with a family history of renal disease (rather than a family history of diabetes), yet associated with diabetes through relative hypoinsulinaemia and hyperglycaemia.63 Diabetic nephropathy among children and young adults with Type-1 diabetes was reportedly 19% in the Waikato area.64
Few studies of diabetic eye and foot disease have been undertaken. A summary is shown in Table 4. The SADP study in 1992–93 found significant ethnic differences in the rates of blindness, laser treatment, and cataract among people with diabetes: Maori and Pacific people having double the proportions as those of European descent.46
Retinopathy was present in 41% of a Type 2 diabetes cohort in Canterbury at baseline.59 A decline in the rates of vision-threatening diabetic retinopathy from 11.5% in 1993 to 1.5% in 2002 has been reported in diabetes patients in the Waikato area, but Maori had a high failure-to-attend-screening rate (32.3%) compared with the overall rate of 18.7%.50 Get Checked results for 2004 indicated low eye-screening rates of less than 70% overall, with less than 60% for Maori and Pacific groups. The rate in those aged under 26 was 13%.64
The prevalence of hospital discharges for diabetic foot disease in New Zealand increased from 13.56 in 1980 to 25.79 in 1993.65 The total inpatient cost for the management of diabetic foot disease in New Zealand (population 3.3 million) for 1993 was estimated to be in the range of NZ$10–11 million.
The SADP study found significantly higher numbers of Pacific peoples with major lesions (amputation or ulcer/blister) compared with European or Maori diabetes patients (Table 4).51 The Ministry of Health estimated that Pacific people have more than double rate of lower limb amputation (43.6 per 100,000) in adults aged 25+ compared with the total New Zealand average (17.4)66 in 2004.
The Auckland Leg Ulcer Study in subjects aged 40+ years showed that 18% of cases had diabetes as a comorbidity whereas only 5.5% of controls had diabetes.67
While the diabetes epidemic continues to impact increasingly on New Zealanders and its health services during the past 5 years, a growing number of Government and DHB-funded initiatives are in place to prevent diabetes and its complications (e.g. Lets Beat Diabetes and Diabetes Projects Trust in Counties-Manukau, Ngati Porou Hauora Ngatai and Healthy Programme in Taiwawhiti, Te Whai Matauranga o te Ahua Noho lifestyle program in Otago, and Te Wai o Rona: Diabetes Prevention Strategy in Waikato/Lakes).
Moreover, several district diabetes registers are in place or are under development (e.g. in Otago, Canterbury, Waikato and South/West Auckland), and these are complemented by the Get Checked data. ANZDATA renal and the emerging Australasian Diabetes in Pregnancy Society diabetes in pregnancy registers, along with a several eye screening registers also contribute to our understanding of diabetes in New Zealand.
The Get Checked dataset is apparently due to be extended, and this may help provide a more detailed and comprehensive view of diabetes and its care. Work is now needed on how best to monitor the incidence and prevalence of diabetes as well as the proportion of people with undiagnosed diabetes, impaired glucose tolerance, and impaired fasting glucose. How else will we know that the growing resources directed towards lifestyle change are having an effect?
To date, the data gathered relating to metabolic control and complications are patchy, however they suggest that New Zealand needs to do more to reduce the impact of diabetes on cardiovascular, renal, eye, foot, and pregnancy related complications. This is particularly the case for Maori and Pacific peoples, whose metabolic control remains poorer than that for European New Zealanders.
More aggressive blood pressure, glycaemic, and lipid control would appear to be needed, and the development of ways to deliver this within the context of New Zealand (i.e. to its people and its health service) are urgently required. Such increases in medication use and services (in both primary and secondary care) are likely to cost more initially and yet little data exists to guide such development.
PricewaterhouseCoopers Ltd estimated that the Type 2 diabetes cost in 2001 approached NZ$400 million and was predicted a rise to more than NZ$1000 million by 2021.68 They also estimated that the total cost of diabetes could be reduced over 20 years if existing services are increased as soon as possible (by $10 million each year in their enhanced services model). The models used are not perfect, yet more complete than the earlier Health Funding Agency report.6 It is surprising that more detailed economic data is not available.
While there have been a relatively large number of publications relating to diabetes in New Zealand over the last 5 years, a significant proportion were from South Auckland in the 1990s and these data are now ageing. More importantly, while services are developing in primary and secondary care, evaluation has rarely been sufficiently robust to lead to publication in peer-reviewed journals. Indeed, funding for such “diabetes translational research” has been uncommon and fits poorly into the existing research funding paradigm.
If we are to develop more complex models of care, and increase access to modern pharmaceuticals and devices, then it is also clear that we need more research into the impact of such service developments on the incidence, prevalence, and costs of diabetes and its complications. While this will not come cheaply, it will be cheaper than the alternative.
A nationally agreed strategic plan is now urgently needed on how best to monitor and control the increasing incidence and prevalence of diabetes. In addition, major national surveys are required now to ascertain the proportion of those people living in New Zealand with impaired fasting glucose or impaired glucose tolerance, as well as those with undiagnosed diabetes.
Author information: Grace Joshy, Research Fellow; David Simmons, Professor of Medicine; Waikato Clinical School, University of Auckland, Hamilton
Acknowledgements: We acknowledge Professor Ross Lawrenson (Head of Waikato Clinical School, University of Auckland), Dr Paul Drury (President, NZSSD), Sandy Dawson (Ministry of Health), and DHB-level diabetes teams for their valuable input.
Correspondence: Grace Joshy, Research Fellow in Diabetes Epidemiology, University of Auckland Waikato Clinical School, Waikato Hospital, Private Bag 3200, Pembroke Street, Hamilton. Fax: (07) 839 8712; email: email@example.com
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