Circulating Thyroid Hormone Profile In Response To A Triiodothyronine Challenge In Familial Longevity

Context: Familial longevity is associated with higher circulating levels of thyrotropin (TSH), in the absence of differences in circulating thyroid hormones, and a lower thyroid responsivity to TSH, as previously observed in the Leiden Longevity Study (LLS). Further mechanisms underlying these observations remain unknown.Objective: We hypothesized that members from long-lived families (offspring) have higher thyroid hormone turnover or less negative feedback effect on TSH secretion compared to controls.Methods: In a case-control intervention study, 14 offspring and 13 similarly aged controls received 100 mu g 3,5,3'-triiodothyronine (T3) orally. Their circulating T3, free T3 (fT3), and TSH levels were measured during 5 consecutive days. We compared profiles of circulating T3, fT3, and TSH between offspring and controls using general linear modeling (GLM) and calculated the percentage decline in TSH following T3 administration.Results: Circulating T3 and fT3 levels increased to supraphysiologic values and normalized over the course of 5 days. There were no serious adverse events.T3 and fT3 concentration profiles over 5 days were similar between offspring and controls (T3 GLM P= .11, fT3 GLM P= .46).TSH levels decreased in a biphasic manner and started returning to baseline by day 5. TheTSH concentration profile over 5 days was similar between offspring and controls (GLM P= .08), as was the relativeTSH decline (%).Conclusions: Members of long-lived families have neither higherT3 turnover nor diminished negative feedback of T3 on TSH secretion.The cause and biological role of elevated TSH levels in familial longevity remain to be elucidated.