Endocrine Abstracts

Objective: Many studies suggest that thyroid function modifies the process of healthy aging in humans. However, both a progressive increase and decrease of TSH with advancing age have been reported. The discrepancy may lie in the iodine intake in the population under, since low iodine intake results in an inverse association of TSH with age, while high iodine intake results in a positive association. We aimed to investigate whether FT₄, FT₃ and FT₃/FT₄-ratio are markers of healthy aging by prospectively investigating their association with mortality in euthyroid subjects.

Design: Prospective case-cohort study within the PREVEND study.

Subjects: A random subcohort of 2703 subjects was drawn from the PREVEND cohort (all aged 28 to 75 years). A total of 260 subjects were excluded from analyses, mainly because of TSH outside the reference range (0.35–4.94 mIU/l; n=115) In this subcohort, 69 subjects died during median follow-up of 5.4 years. During follow-up, 164 subjects died in the remaining part of the entire cohort. Of these, 141 remained for analyses after the exclusion criteria were applied. These subjects constituted the ‘external’ cases.

Results: After adjustment for age and sex, FT₄ was positively and FT₃/FT₄-ratio was inversely associated with cardiovascular mortality (HR, 95% CI: 1.38, 1.06–1.78, P=0.02 and 0.65, 0.48–0.89, P=0.006 respectively). Both FT₃ and FT₃/FT₄-ratio were inversely associated with all-cause mortality (HR, 95% CI: 0.66, 0.57–0.77, P<0.0001 and 0.67, 0.57–0.79, P<0.0001 respectively) and non-cardiovascular mortality (HR, 95% CI: 0.61, 0.51–0.73, P<0.0001 and 0.65, 0.54–0.79, P<0.0001 respectively).

Conclusions: We prospectively found that FT₄, FT₃ and FT₃/FT₄-ratio predicted mortality in euthyroid subjects: high FT₄ and low FT₃/FT₄-ratio were associated with cardiovascular mortality and low FT₃ and low FT₃/FT₄-ratio were associated with all cause mortality and non-cardiovascular mortality.