Iodine in drinking water varies by more than 100-fold in Denmark. Importance for iodine content of infant formulas

The iodine intake level of the population is of major importance for the oc currence of thyroid disorders in an area. The aim of the present study was to evaluate the importance of drinking water iodine content for the known r egional differences in iodine intake in Denmark and for the iodine content of infant formulas. Iodine in tap water obtained from 55 different locations in Denmark varied from <1.0 to 139 mu g/l. In general the iodine content was low in Jutland ( median 4.1 mu g/l) with higher values on Sealand (23 mu g/l) and other isla nds. Preparation of coffee or tea did not reduce the iodine content of tap water with a high initial iodine concentration. A statistically significant correlation was found between tap water iodine content today and the urina ry iodine excretion measured in 41 towns in 1967 (r=0.68, P < 0.001). The c orrelation corresponded to a basic urinary iodine excretion in Denmark of 4 3 mu g/24h excluding iodine in water and a daily water intake of 1.71. The iodine content of infant formulas prepared by addition of demineralized wat er varied from 37 to 138 mu g/l (median 57 mu g/l, n = 18). Hence the final iodine content would depend heavily on the source of water used for prepar ation. We found that iodine in tap water was a major determinant of regional diffe rences in iodine intake in Denmark. Changes in water supply and possibly wa ter purification methods may influence the population iodine intake level a nd the occurrence of thyroid disorders.