In populations characterized by long-standing iodine deficiency
and a rapid increase in iodine intake, median values for urinary iodine
above 200 μg/l (and in pregnant women, above 250 μg/l) are not recommended
because of the possible risk of iodine-induced hyperthyroidism.
This adverse condition can occur during the 5 to 10 years following the
introduction of iodized salt (24,31). Beyond this period of time, median
values up to 300 μg/l have not demonstrated side-effects, at least not
in populations with adequately iodized salt. In schoolchildren, urinary
iodine concentrations >500 μg/l are associated with increasing thyroid
volume, which reflects the adverse effects of chronic iodine excess (32).