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

Abstract

OBJECTIVESWe 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.DESIGNCross‐sectional study.SETTINGActive and retired employees from public institutions located in six Brazilian cities.PARTICIPANTSA 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.METHODSSerum 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).RESULTSThe 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.CONCLUSIONSubtle 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.

Age-specific associations of serum TSH levels with markers of body composition in two population-based studies

“…In that studies no signi cant associations of subclinical hypothyroidism with FFM were demonstrated. These ndings are in agreement with a large population-based study from Brazil, in which no association between serum TSH levels and FFM determined by BIA was observed 17 . Another Brazilian study, however, demonstrated a signi cant positive association of serum TSH levels at baseline with a low muscle mass index (as de ned as muscle mass in arms and legs divided through BMI) at follow-up in 408 women older than 65 years 16 .…”

“…Another Brazilian study, however, demonstrated a signi cant positive association of serum TSH levels at baseline with a low muscle mass index (as de ned as muscle mass in arms and legs divided through BMI) at follow-up in 408 women older than 65 years 16 . The different ndings of that study 16 to our and other studies 14,15,17 may be explained by different study populations (only women included), different histories of iodine supply and particularly by different outcome de nitions. While our and the other studies were focusing on total FFM 14,15,17 , Machado et al looked at appendicular muscle mass, an outcome which may be more tightly related to muscle strength than to total FFM.…”

“…The different ndings of that study 16 to our and other studies 14,15,17 may be explained by different study populations (only women included), different histories of iodine supply and particularly by different outcome de nitions. While our and the other studies were focusing on total FFM 14,15,17 , Machado et al looked at appendicular muscle mass, an outcome which may be more tightly related to muscle strength than to total FFM. In line with this assumption previous studies showed signi cant associations between high TSH values and muscle strength determined by a handgrip strength test 17,25 .…”

“…While our and the other studies were focusing on total FFM 14,15,17 , Machado et al looked at appendicular muscle mass, an outcome which may be more tightly related to muscle strength than to total FFM. In line with this assumption previous studies showed signi cant associations between high TSH values and muscle strength determined by a handgrip strength test 17,25 .…”

“…All other studies on such potential associations were conducted in the elderly and revealed con icting results [14][15][16][17] . In a study with 408 women ≥ 65 years old serum TSH levels at baseline were associated with low appendicular muscle mass after a mean follow-up time of 4.3 years 16 , whereas in a cross-sectional population-based study with 6974 individuals ≥ 50 years serum TSH levels were not associated with muscle mass determined by bioelectrical impedance analysis (BIA) 17 . Furthermore, one cross sectional 15 and one longitudinal 14 population-based study failed to demonstrate signi cant associations between subclinical hypothyroidism and FFM.…”