TSH levels are associated with vitamin D status and seasonality in an adult population of euthyroid adults

A circannual periodicity in thyrotropin (TSH) secretion has been reported but the causes of these phenomenon are still undefined. Vitamin D exerts a direct influence on pituitary axes including the hypothalamus–pituitary–thyroid axis. Aims of the present study were to investigate the presence of a seasonal variability of TSH secretion and to study the association between vitamin D status and TSH levels in a population of euthyroid adults. For...