Abstract
The relative absence of iodised salt from the Irish diet which latest figures indicate has declined from ~ 4% to <1% of salt sales has resulted in Urinary Iodine (UI) excretion being consistent with borderline iodine deficiency. Previous studies in Ireland and other northern European countries have found a seasonal variation in iodine intake with intakes being lower in the summer months. This seasonal variation has been attributed to agricultural practices with milking cattle being kept indoors in winter and fed iodine containing supplements. In order to chart the impact of this recent decline in UI, urine samples were obtained each month from first trimester pregnant women (N= 429) attending the National Maternity Hospital, Dublin over the calendar year 2007. UI was measured using the multiplate ammonium persulphate digestion method. Median UI was 79µg/L (115µg/ g Creatinine) over the 12month period reaching a monthly maximum of 99µg/L in November and a minimum of 48µg/L in April. There was a significant seasonal variation in UI (p=0.002; Mann-Whitney test) with the median UI of the winter months (Oct-Mar) 89ug/L with the summer (April- Sept) median UI 74ug/L. More values suggestive of iodine deficiency (><50ug/L) were found in the summer (34%) than in the winter (23%) months (p=0.01; chi-squared test). The findings indicate that a seasonal variation in UI continues to exist in the Irish population. In the absence of salt iodization, dietary iodine intake is entirely opportunistic putting the unborn fetus at unnecessary risk particularly those conceived in the low iodine summer months and indeed in those whose consumption of dairy products is minimal.