Bano A, et al. - This study was conducted to determine the association of thyroid function with total life expectancy (LE) and life expectancy (LE) with and without cardiovascular disease (CVD) among euthyroid individuals. Collected data represented that at the age of 50 years, participants with low-normal thyroid function live up to 3.5 years longer overall and up to 3.1 years longer without CVD than participants with high-normal thyroid function. These results indicated the need for a reevaluation of the current reference ranges of thyroid function, which would aid in preventive and clinical care.

Methods

• This study enrolled subjects without known thyroid disease and with thyrotropin and free thyroxine (FT₄) levels within the reference ranges.
• Among thyrotropin and FT₄ tertiles, multistate life tables were used to calculate total LE and LE with and without CVD.
• Prevalence, incidence rates, and hazard ratios for 3 transitions (healthy to CVD, healthy to death, and CVD to death), adjusting for sociodemographic and cardiovascular risk factors were used to calculate life expectancy estimates in men and women aged 50 years and older.

Results

• The mean (SD) age of the 7785 participants was 64.7 (9.8) years, and 52.5% were women. 
•  Over a median follow-up of 8.1 (interquartile range, 2.7-9.9) years, 789 incident CVD events and 1357 deaths were reported.
• Compared with those in the lowest tertile, men and women in the highest thyrotropin tertile lived 2.0 (95% CI, 1.0 to 2.8) and 1.4 (95% CI, 0.2 to 2.4) years longer, respectively, of which, 1.5 (95% CI, 0.2 to 2.6) and 0.9 (95% CI, -0.2 to 2.0) years longer without CVD. 
• Compared with those in the lowest tertile, the difference in life expectancy for men and women in the highest FT₄ tertile was -3.2 (95% CI, -5.0 to -1.4) and -3.5 (95% CI, -5.6 to -1.5) years, respectively, of which, -3.1 (95% CI, -4.9 to -1.4) and -2.5 (95% CI, -4.4 to -0.7) years without CVD.