REDUCED THYROID ACTIVITY IN JAMAICANS

Abstract

SUMMARY The results presented demonstrate reduced thyroid activity in euthyroid Jamaicans. In 15 subjects, thyroid clearance of 131I was 13·0 ± 8·8 (s.d.) ml/min, and renal clearance was 20·6 ± 9·7 ml/min. In 205 healthy volunteers the 24 h 131I thyroid uptake averaged 13·8% and in 60·9% the uptake was less than 10% of the dose. Urinary excretion of 131I was correspondingly high. However, excretion of stable iodine in urine averaged only 62·0 μg/day. Thyroid secretion rate (TSR) calculated in a group of subjects with complete collection of urine was 12·0 μg I/day in women and 11·4 μg I/day in men. Protein-bound iodine (PBI) values in 50 subjects were 5·9 ± 1·3 μg/100 ml. Uptake of tri-iodothyronine by red blood cells also gave low values. The apparent discrepancy between low TSR and normal PBI is discussed. These findings, together with other reported values, indicate reduced thyroid activity in the tropics. It is argued that reduced metabolism is probably secondary to lower thyroid activity.