Iodine intake and status of UK women of childbearing age recruited at the University of Surrey in the winter.

Abstract

As intra-thyroidal iodine stores should be maximised before conception to facilitate the increased thyroid hormone production during pregnancy, women who are planning to become pregnant should ideally consume 150μg iodine/d (US RDA). As few UK data exist for this population group, a cross-sectional study was carried out at the University of Surrey to assess the iodine intake and status of women of childbearing age. Total iodine excretion was measured from 24h urine samples in fifty-seven women; iodine intake was estimated by assuming that 90% of ingested iodine was excreted. The average iodine intake was also estimated from 48h food diaries that the participants completed. The median urinary iodine concentration value (63·1μg/l) indicated the group to be mildly iodine deficient by WHO criteria. By contrast, the median 24h urinary iodine excretion value (149·8μg/24h) indicated a relatively low risk of iodine deficiency. The median estimated iodine intake, extrapolated from urinary excretion, was 167μg/d, whereas it was lower, at 123μg/d, when estimated from the 48h food diaries. Iodine intake estimated from the food diaries and 24h urinary iodine excretion were strongly correlated (r 0·75, P<0·001). The intake of milk, eggs and dairy products was positively associated with iodine status. The iodine status of this UK cohort is probably a best-case scenario as the women were mostly nutrition students and were recruited in the winter when milk-iodine content is at its highest; further study in more representative cohorts of UK women is required. The present study highlights the need for revised cut-off values for iodine deficiency that are method- and age group-specific.