Inadequate dietary iodine intake is the most common cause of preventable mental impairment worldwide and is defined by the WHO as a population median urinary iodine (UI) excretion <100 μg/l. No contemporary data are available for the UK according to the ICCIDD. The UK has no programme of food/salt iodination.
We have performed a systematic assessment of the current UK iodine status in 1415 years old schoolgirls. Seven hundred and eighty-five participants from nine UK centres provided 737 urine samples. UI concentrations were measured as μg iodine/l by a multiplate persulphate digestion method followed by SandelKolthoff colorimetry in specimens collected in Summer 2009 and Winter 2009/2010. Ethnicity, postcode and a diet questionnaire assessing sources of iodine were recorded. Iodine concentrations were also measured in water samples from each area.
The median UI value for this sample was 80 μg/l with 69% of samples <100 μg/l and 18% <50 μg/l. A multivariate regression analysis confirmed as independent factors a difference in summer versus winter iodine status (R2 0.2, P<0.001) with the median nadir of 76 μg/l in summer and a positive association with milk intake (R2 0.2, P<0.001). There was no correlation with other foods, ethnicity or city of origin.
These findings suggest that the UK is now iodine-deficient, consistent with a fall in iodine status recently reported in Australia and USA. Young women of child-bearing age are the most susceptible to the adverse effects of iodine deficiency. Even mild perturbations of fetal and maternal thyroid function have an impact upon neurodevelopment so these findings are consequently of huge public health importance. These findings indicate an urgent need for a comprehensive investigation of UK iodine status and evidence based recommendations on the need to implement a policy of iodine prophylaxis.
Generously funded by the Clinical Endocrinology Trust.