Iodine status of postpartum women and their infants aged 3, 6 and 12 months - Mother and Infant Nutrition Investigation (MINI).

Abstract

To alleviate the re-emergence of iodine deficiency in New Zealand, two strategies, the mandatory fortification of bread with iodised salt (2009) and a government-subsidised iodine supplement for breastfeeding women (2010) were introduced. Few studies have investigated mother and infant iodine status during the first postpartum year, this study aimed to describe iodine status of mothers and infants at three, six, twelve months postpartum (3MPP,6MPP,12MPP). Partitioning of iodine excretion between urine and breastmilk of exclusive breastfeeding women at 3MPP was determined. In total 87 mother-infant pairs participated in the study. Maternal and infant spot urinary iodine concentration (UIC) and breastmilk iodine concentration (BMIC) were determined. The percentage of women who took iodine-containing supplements decreased from 46% at 3MPP to 6% at 12MPP. Maternal median UIC (MUIC) at 3MPP [82(46,157)µg/L], 6MPP [85(43,134)µg/L] and 12MPP [95(51,169)µg/L] < 100µg/L. The use of iodine-containing supplements increased MUIC and BMIC only at 3MPP. Median BMIC at all time points were below 75µg/L. Infant MUIC at 3MPP [115(69,182)µg/L] and 6MPP [120(60,196)µg/L] were below 125µg/L. Among exclusive breastfeeding women at 3MPP, an increased partitioning of iodine into breastmilk (highest proportion 60%) was shown at lower iodine intakes, along with a reduced fractional iodine excretion in urine (lowest proportion 40%), indicating a protective mechanism for breastfed infants iodine status. In conclusion, this cohort of postpartum women was iodine deficient. Iodine status of their breastfed infants were suboptimal. Lactating women who do not consume iodine rich foods and those who become pregnant again should take iodine-containing supplements.