The association of milk and dairy consumption with iodine status in pregnant women in Oporto region

The role of milk and dairy products in supplying iodine to pregnant women is unknown in Portugal. The aim of this study was to evaluate the association between milk and dairy consumption and the iodine status of pregnant women in the IoMum cohort of the Oporto region. Pregnant women were recruited between 10 and 13 weeks of gestation, when they provided a spot urine sample and information on lifestyle and intake of iodine-rich foods. Urinary iodine concentration (UIC) was determined by inductively coupled plasma mass spectrometry. A total of 468 pregnant women (269 iodine supplement users and 199 non-supplement users) were considered eligible for analysis. Milk (but not yoghurt or cheese) intake was associated with UIC, in the whole population (p = 0.02) and in the non-supplement users (p = 0.002), but not in the supplement users (p = 0.29). In non-supplement users, adjusted multinomial logistic regression analysis showed that milk consumption < 3 times a month was associated with a 5 times increased risk of having UIC < 50 μg/L when compared to milk consumption ≥ 2 times a day (OR = 5.4; 95% CI: 1.55-18.78; p = 0.008). The highest UIC was observed in supplement users who reported consuming milk once a day (160 μg/L). Milk, but not yoghurt or cheese, was positively associated with iodine status of pregnant women. Despite the observed positive association, daily milk consumption may not be sufficient to ensure adequate iodine intake in this population.