Abstract
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 <160 µg I/day, respectively. The percentage of women who identified health problems associated with inadequate iodine were: goitre (32%), mental retardation (21%) and ‘don’t know’ (40%). Percentages of women who identified good iodine food sources included: salt (73%), bread (42%), seafood (34%), milk (16%) and eggs (17%).
Conclusions: This study indicates that although fortification and supplementation have improved iodine status in pregnant women (UIC from 38 µg /L in 2005 to 105 µg /L in 2013), these data suggest that pregnant women in New Zealand still have sub-optimal iodine status. Further research is needed to ascertain whether an iodine supplement with a higher dose of iodine would improve iodine status. Based on the relatively high percentage of women who did not take an iodine supplement, consistent iodine education provision from healthcare providers to their pregnant women combined with enhanced public health education targeting populations at risk of iodine inadequacies appears warranted.