An increase of plasma triiodothyronine concentration in man in a cold environment

In an attempt to study an effect of cold on endocrine function in man, plasma thyroxine (T4), triiodothyronine (T3), TSH, and cortisol concentrations were studied in 24 healthy men who worked in a cold environment (4 to 6C) for 3 h for the culture of mushrooms and 56 healthy men who lived in cold environment in winter. For comparison, similar measurements were made on 47 university employees who lived in rooms with air-conditioning. In 24 adult men, acute exposure to cold for 3 h failed to affect plasma concentrations of T4, T3, and TSH. In 56 adult men, no significant difference was found in the concentrations of T4, TSH, and cortisol between summer and winter. However, plasma T3 concentration increased significantly in winter, suggesting seasonal variation of T3. In contrast, no such seasonal variation was found in 47 university employees who lived in rooms with air-conditioning.