Seasonal Changes in Iodine Metabolism

Regional differences in the prevalence of goitre in Britain were recognized during the early part of the last century The importance of iodine deficiency in the pathogenesis of goitre has been established beyond reasonable doubt, though it is now clear that other factors may also be important in the development of thyroid enlargement. In the past considerable attention has been paid to the concentration of iodine in water-supplies (Murray, Ryle, Simpson, and Wilson, 1948) but in Britain this usually lies between 1 and 4 ptg./litre. Consequently the human requirement of iodine for health, often placed at about 100 /Ag. a day, must be met largely from the diet. The food richest in iodine is undoubtedly marine fish (Chilean Iodine Educational Bureau, 1952), but this is only an occasional item in the diet. Another foodstuff relatively rich in iodine is cows' milk, and this is important, particularly in childhood, as it is consumed daily in large amounts. During the course of investigations into the pathogenesis of non-toxic goitre a large seasonal fluctuation was observed in the iodine content of milk which entirely overshadowed any regional differences. The extent and cause of this fluctuation in iodine concentration were accordingly investigated further.