Thyroid Function and Sarcopenia: Results from the ELSA‐Brasil Study

OBJECTIVES We aimed to investigate the association of subclinical thyroid disease and thyroid hormone levels with sarcopenia and its defining components in community‐dwelling middle‐aged and older adults without overt thyroid dysfunction. DESIGN Cross‐sectional study. SETTING Active and retired employees from public institutions located in six Brazilian cities. PARTICIPANTS A total of 6974 participants from the ELSA‐Brasil study's second wave, aged 50 years and older, without overt thyroid dysfunction and with complete data for exposure, outcome, and covariates. METHODS Serum levels of thyrotropin (TSH), free thyroxine, and free triiodothyronine (FT3) were measured and divided in quintiles for the analyses. Participants were classified with euthyroidism, subclinical hypothyroidism, and subclinical hyperthyroidism. Muscle mass was assessed by bioelectrical impedance analysis and muscle strength by handgrip strength. Sarcopenia was defined according to the Foundation for the National Institutes of Health criteria. Possible confounders included sociodemographic characteristics, clinical conditions, and lifestyle. Analyses were performed separately for middle‐aged and older adults (≥65 y). RESULTS The frequencies of sarcopenia, low muscle mass, low muscle strength, subclinical hypothyroidism, and subclinical hyperthyroidism were 1.5%, 20.8%, 3.8%, 9.1%, and .9%, respectively. Subclinical thyroid dysfunction was not associated with sarcopenia and its defining components. Among older adults, TSH had a U‐shaped association with sarcopenia and low muscle strength. The odds ratios (ORs) (95% confidence intervals [CIs]) for the associations of the first, second, fourth, and fifth quintile with sarcopenia, respectively, were 5.18 (1.47‐18.28), 6.28 (1.82‐21.73), 4.12 (1.15‐14.76), and 4.81 (1.35‐17.10), and with low muscle strength was (OR (95% CI) for the first, second, and fifth quintiles, respectively: 1.43 (1.16‐5.07), 2.07 (1.24‐4.70), and 2.18 (1.03‐4.60). Additionally, FT3 had a negative association with muscle mass in both age strata. CONCLUSION Subtle thyroid hormone alterations are associated with sarcopenia or its defining components in middle‐aged and older adults without overt thyroid dysfunction. J Am Geriatr Soc 68:1545‐1553, 2020.