Cow Milk Consumption Increases Iodine Status in Women of Childbearing Age in a Randomized Controlled Trial

Background: Recent evidence has highlighted the prevalence of mild-to-moderate iodine deficiency in women of childbearing age and pregnant women, with important public health ramifications owing to the role of iodine, required for thyroid hormone production, in neurodevelopment. Cow’s milk contributes the greatest amount to iodine intakes in several countries. Objective: The objective of this study was to investigate the effect of increased cow’s milk consumption on iodine status, thyroid hormone concentrations and selenium status. Methods: A 12 week, randomized-controlled trial was conducted in 78 low-moderate milk consuming (<250ml/d) healthy women (18-45 years). The intervention group were asked to consume 3L of semi49 skimmed milk per week, while the control group continued their usual milk consumption (baseline median (IQR): 140 (40-240) mL/d). At baseline, week 6 and week 12 participants provided a spot51 urine sample [urinary iodine concentration (UIC); creatinine] and a fasting blood sample [thyroid hormone concentrations; serum total selenium; selenoprotein P]. This study was registered at ClinicalTrials.gov Study (Ref: NCT02767167). Results: At baseline, the median (IQR) UIC of all participants was 78.5 (39.1-126.1)μg/L. Changes in the median UIC from baseline to week 6 (35.4 vs. 0.6 μg/L; P=0.014) and week 12 (51.6 vs. -3.8 μg/L; P=0.045) were significantly greater in the intervention group compared with the control group. However, despite being higher within the intervention group at weeks 6 and 12, the change in the iodine:creatinine ratio from baseline was not significantly different between groups at either week 6 (P=0.637) or 12 (P=0.178). There were no significant differences in thyroid hormone concentrations or selenium status between groups at any time point. Conclusions: The present study has demonstrated that the consumption of additional cow’s milk can significantly increase UIC in women of childbearing age. These results suggest that cow’s milk is a potentially important dietary source of iodine in this population group.