Free and total triiodothyronine and thyroxine in malnourished Jamaican infants. The effect of diet on plasma levels of thyroid hormones, insulin and glucose during recovery.

Plasma concentrations of free triiodothyronine (FT3), total triiodothyronine (TT3) and total thyroxine (TT4) were reduced to 63.0, 37.7, 61.7 per cent of controls respectively in protein-energy malnutrition (PEM), while free thyroxine (FT4) was elevated by 23 per cent. There was a gradual increase of both TT4 and TT3 during recovery. The ratio of free to bound hormones was high in malnutrition and declined with recovery, indicating a deficiency of thyroid-hormone binding in malnutrition. The observation of a significant reduction (P less than 0.05) in T3/T4 ratios, which occurred in malnutrition and was induced during recovery after 3 d on a low energy maintenance diet, suggested depressed conversion of T4 to T3 due to energy restriction. Energy restriction also significantly (P less than 0.001) depressed plasma insulin concentrations in the presence of nearly constant plasma glucose levels.