Iodine status in pregnant New Zealand women: Are intakes and recommendations adequate?

Primary health care Diet Maternal and infant welfare Pregnancy New Zealand

Background: Iodine requirements increase in pregnancy as both the mother and foetus need iodine for the synthesis of thyroid hormones. In response to a re-emergence of iodine deficiency in New Zealand in the 1990s, bread was fortified with iodised salt in 2009 and a recommendation for a daily supplement of 150 µg iodine in pregnancy has been in place since 2010. Objectives: The aim of this study was to assess the iodine status of pregnant women to determine the effectiveness of these strategies in achieving adequate iodine status.Methods: A convenience sample of 100 pregnant women was recruited from each of three centres (Dunedin, Hamilton and Wellington) between July 2012 to December 2013. Women were asked to collect a spot urine sample to determine urinary iodine concentration (UIC), urinary iodine per gram creatinine and complete a questionnaire to obtain socio-demographic information, iodine supplement use, and frequency of consumption of iodine-containing foods. Results: The final sample size was 302 women with a mean age of 31±5 years of the following ethnicity: 87% NZ European and other ethnicities, 13% Māori and Pacific Island. The median UIC was 105 µg/L; this falls below 150-250 µg/L suggested by the World Health Organization for adequate iodine status in pregnancy. Median urinary iodine per gram creatinine was 153 µg/g; no established recommendation guidelines exist for pregnant women, however, >150 µg/g was used as an indicator of adequate iodine status. Despite the recommendation for daily iodine supplementation, 35% of women did not take an iodine supplement. The median iodine intakes from food alone, food including iodised salt use, and total iodine intake including an iodine supplement were 76 µg/day, 113 µg/day and 236 µg/day, respectively. The estimated average requirement (EAR) of iodine in pregnant women is 160 µg/day; the food frequency questionnaire suggested that 61% of women met the EAR when iodine intake included iodine from supplements and discretionary salt while only 1% of women met the EAR without the supplement. Seventy four percent of women used iodised salt in cooking or at the table. Iodine supplementation was a significant predictor of UIC (p=0.048) and urinary iodine per gram creatinine (p=0.001) in multivariate analysis linear regression. Education and ethnicity were significant predictors of urinary iodine per gram creatinine in multivariate analysis linear regression (p= 0.035 and p=0.044, respectively). Ethnicity and income were significant predictors of total iodine intake using multivariate analysis linear regression, (p= 0.044 and p=0.011, respectively). Multivariate analysis showed that UIC and urinary iodine per gram creatinine in women who took a supplement containing >160 µg I/day were 1.30 times and 1.46 times higher than those who took no supplement or one containing

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