Abstract
Iodine, through thyroid hormones, is required for fetal brain development during pregnancy. Iodine deficiency was historically common in the UK and was eradicated, not by the usual practice of an iodised-salt programme, but through an adventitious increase in milk-iodine concentration. There is a dearth of information on iodine status and food sources of iodine in the UK which this thesis has endeavoured to address through a series of studies. The thesis has highlighted several causes for concern: (1) The median urinary-iodine concentration in pregnant women in Surrey and Oxford (85. 3 and 42. 5 μg/L respectively) is indicative of iodine deficiency; (2) higher iodine status was associated with use of an iodine-containing supplement and the major dietary predictor of iodine status (assessed through a food-frequency questionnaire) was milk and dairy produce. A study of retail milk revealed organic milk to have an iodine concentration 42% lower than that of conventional milk and is thus a potential threat to iodine status; (3) in contrast to other countries worldwide, iodised salt availability is low in the UK and fewer than 20% of supermarket shoppers have iodised salt available to purchase; thus iodised salt is not likely to contribute to UK iodine status; (4) 15% of pregnant women in Oxford had a low free-thyroxine concentration which may pose a threat to the developing fetal brain and finally; (5) iodine deficiency, as assessed in stored-urine samples of a UK prospective cohort study was associated with adverse effects on neurological development; children of iodine-deficient women had a higher risk of low IQ at age 8 (OR 1. 58, 95% Cl 1. 09-2. 29) and poorer reading accuracy scores at age 9 (OR 1. 83, 95% Cl 1. 22-2. 74), even after adjustment for potential confounders. The findings suggest that a UK public-health policy is required to minimise the adverse effects of iodine deficiency.