The current New Zealand guideline recommends iodine-only supplementation (150µg/day) is needed during breastfeeding to meet increased iodine requirements, even for women with a well-balanced diet.[[1]] In 2009, mandatory fortification of bread with iodised salt was introduced in New Zealand[[2]]—this was expected to improve the iodine status of the general population, but was not sufficient to meet the increased needs of pregnant and lactating women. In 2010, a major Government initiative was launched in New Zealand to provide iodine-only supplements for all pregnant and lactating women.[[1]] In 2021, the Mother and Infant Nutrition Investigation (MINI), an observational longitudinal cohort study spanning the first postpartum year, recruited 87 breastfeeding mother–infant pairs in New Zealand.[[3]] This study found that, for women who did not take iodine supplements, both mothers and their infants were iodine deficient at three months postpartum.[[4]] Iodine deficiency can compromise the thyroid function of both the mother and her breastfed infant, which would be exacerbated if the woman became pregnant again soon.[[5]]

The MINI study reported that 46% (40/87) of breastfeeding women at three months postpartum took iodine supplements in the 24hr period prior to the data collection,[[3]] and throughout the first postpartum year the percentage of breastfeeding women using iodine supplements declined (to 11% at six months and 6% at 12 months).[[4]] A 2019 cross-sectional online survey of New Zealand breastfeeding women reported 63% (179/284) used iodine supplements within the first six months postpartum.[[6]] Data showed much lower usage amongst breastfeeding mothers than was expected, which implies a failure of adhering to the current iodine supplementation recommendation in New Zealand.

Adequate iodine supply is required for the optimal production of the thyroid hormones, triiodothyronine and thyroxine, which are essential for the development of the central nervous system during the first 1,000 days of a child’s life.[[7]] It can take several weeks for absorbed iodine to be incorporated into thyroid hormones, thus it is essential to achieve adequate intrathyroidal iodine stores periconceptually is to allow for the increased thyroid hormone production during pregnancy and after parturition.[[8]] During lactation, iodine is required for maternal thyroid function and is secreted into breastmilk to ensure adequate iodine supply for optimal infant thyroid function and neurological development.[[9]] In New Zealand, women are recommended to use iodine-only supplements once pregnancy is confirmed until they cease breastfeeding completely, as well as consuming balanced diet to ensure optimal infant brain development.[[1]]

The cross-sectional online survey of New Zealand women reported 81% of lactating women who used iodine supplements did so because of advice given by health professionals.[[6]] The most frequently reported reason for not taking supplements in the MINI study was women were not specifically advised to do so by a health professional.[[3]] Although women may be provided with a prescription for iodine supplements by their health professional, this may be too costly for those who are already on a tight budget or require extra travel or transportation for collection of supplements from their pharmacy. A 2016–2017 New Zealand online survey reported 13% of women who received prescriptions for iodine supplementation did not collect their prescriptions,[[10]] however, reasons for this were not stated.

In New Zealand, six weeks after childbirth, the medical care for mothers and their infants’ transfers from their lead maternity carer (Midwife or Obstetrician) to their general practitioner (GP), in conjunction with child nurses (i.e., Tamariki Ora or Whānau Āwhina). These health professionals are well-placed to provide timely and comprehensive advice to postpartum women. Strategies to reduce barriers for women to access Government-subsided iodine-only supplements are needed. For example, removing the cost of dispensing fee at pharmacy, having such free supplements available at midwife or GP clinics, so that women who require them can collect them immediately, or midwives could get a supply of iodine on practitioner supply order to give to women when they attend visits. There is an urgent need for greater public awareness and information sharing through the health professionals including pharmacists in New Zealand, to promote iodine specific nutrition advice including: 1) the importance of iodine in maternal health; 2) the existing recommendations of taking iodine-only supplementation (150µg/day) for all pregnant and breastfeeding women; and 3) to encourage the routine prescription of Government-subsided iodine-only supplements, which is more affordable for all lactating women. Proactively increasing knowledge of the benefits of iodine supplementation during breastfeeding through health professionals and others who are well-placed to provide such information and support to future mothers, will raise awareness of what can be seen as an ongoing barrier to good maternal and infant health in New Zealand.