| Bülow Pederson et al., Denmark, registered new cases of hyper- and hypothyroidism in two areas of Denmark i.e. Aalborg with moderate iodine deficiency (mean urinary iodine 45 µg/l), and Copenhagen with mild iodine deficiency (61 µg/l). The registration started one year before and two years after a low grade of iodine prophylaxis became available by the voluntary use of iodized table salt (1998). In moderate iodine deficiency the incidence rates of hyperthyroidism in these 3 years were 119.7, 129.9 and 127.7 per 100.000/year as compared to 83.3, 81.3 and 84.3 per 100.000/year (p < 0.01) in mild iodine deficiency. The figures for hypothyroidism were 29.0, 27.6 and 35.4 per 100.000/year, and 50.7. 50.5 and 52.0 per 100.000/year (p < 0.01) respectively. No significant changes in hyper- and hypothyroidism in both areas occurred during this 3 year observation period. The results show that even small differences in iodine intake are associated with considerable differences in incidence of hyper- and hypothyroidism i.e. an increased incidence of hyperthyroidism in moderate iodine deficiency versus an increased incidence of hypothyroidism in mild iodine deficiency. Overall these data show that a considerable decrease in rate of hyperthyroidism but an almost double increase in rate of hypothyroidism occurs when shifting from moderate to mild iodine deficiency. Boyage et al., Fremantle, Westmead and Gosford, Australia, reported two studies. One was conducted in India in 128 children, age 4-5 years, with sufficient iodine intake (median urinary iodine 279 µg/l). Despite this more than adequate iodine intake they (still!) found a significant negative correlation between iodine excretion and thyroid volume. The authors question if this correlation is due to the presence of dietary goitrogens or due to a residual effect of previous iodine deficiency. The nutritional status of these children was good. The other report was conducted in Australia, in 324 primary school children aged 5-13.1 years having a median urinary iodine excretion of 82 µg/l. Only 14% of subjects had values below 50 µg/l. No goiter formation in these children despite less than optimal iodine excretion. The thyroid volume of these children appeared to be much smaller than the normative values proposed by WHO/ICCIDD and the authors underline the importance of local reference values for the interpretation of thyroid volumes in the sense of goitrous or non-goitrous. They also state that conclusions with regard to absence or presence of endemic goiter purely from median urinary iodine excretion values is insufficient when studies are performed in areas with marginal iodine deficiency. (Comment: I would say also in iodine sufficient areas, see the above results from India.) |
