Endocrine Abstracts

Context: Iodine is an important mineral essential for thyroid function and for normal development of the fetus. There is growing evidence that iodine insufficiency is still a major health issue globally.

Objective: The main aim of this study was to look for ethnic differences in iodine status in pregnant women based on urinary iodine concentration (UIC) and food frequency questionnaires (FFQ). Furthermore, we assessed the influence of iodine status on thyroid function.

Methods: Data from the STORK Groruddalen study, a population-based cohort of healthy women (n = 823) with multiethnic background residing in Groruddalen, Oslo, Norway was used. Fifty-two % of participants were of ethnic minority background. Based on a spot sample of morning urine collected in week 15 (n= 654), we calculated weight corrected iodine intake CII_UIC (UIC µg/l x weight (kg) x 0.0235) to estimate iodine status. We also computed an estimated iodine intake score based on data from a semi-quantitative, interviewer administered FFQ in week 28, (n = 727). Combined UIC and dietary data was available for 601 participants.

Results: Median UIC was 89 µg/l (IQR 51; 127). The estimated iodine intake (CII_UIC) was 131 µg/d (IQR 84;217). Based on CII_UIC, the proportion of women with severe iodine insufficiency (CII_UIC <50) was 4-15% in different ethnic groups, and high/excessive (>500) in 4-13%. However, no significant difference was seen between different ethnic groups. Based on FFQ, the median iodine intake was 144 µg/d (IQR 75;219). The lowest iodine intakes were found in Middle East women and the highest levels in South Asian women (P < 0.084). Dairy items contributed to 31% and Fish 29% of the total iodine intake, both with significant differences between ethnic groups (respectively P < 0.019 and P = 0.033). Seventeen percent of the participants reported regular use of iodine containing supplements. We observed higher levels of free thyroxin at week 28 in groups with moderate and highest iodine intake (P < 0.004). However, no significant differences were seen in TSH levels.

Conclusion: Based on US Institute of Medicine’s recommended equation to estimate daily iodine intake in pregnancy, our results indicate that a large group of pregnant women present mild iodine insufficiency. However. The estimated urinary or dietary iodine status did not affect thyroid function consistently, and no significant differences were found between ethnic groups. Larger studies are needed to confirm these findings, and further to assess the effect of mild iodine insufficiency on development of the fetus.