Seasonal variation of stable intrathyroidal iodine in nontoxic goiter disclosed by x-ray fluorescence.

The intrathyroidal stable iodine (ITI) determined in 776 patients chosen at random. Ninety % of these patients presented with nontoxic goiter. Curve-filtering analysis techniques showed a seasonal variation in ITI: an acrophase was found in April/May, a nadir in September/October. The possible relationship of this seasonal variation with the intake of iodine or alimentary antithyroid substances are discussed, as well as possible relationship with variation in chronic TSH stimulation related to ambient temperature.