Association of Serum TSH With Handgrip Strength in Community-Dwelling Euthyroid Elderly

Postmenopausal women with higher TSH values within the normal range present improved handgrip strength: a pilot study

OBJECTIVE

To evaluate the possible association between thyroid function within the euthyroid range and musculoskeletal parameters as well as body composition in a sample of postmenopausal women.

METHODS

This cross-sectional study included 96 postmenopausal women with serum thyroid-stimulating hormone (TSH) within the normal laboratory reference range. Fasting venous blood samples were obtained for biochemical/hormonal assessment. Bone status and body composition were measured using Dual Energy X-ray absorptiometry (DXA). Physical activity was quantified using the International Physical Activity Questionnaire (IPAQ) index.

RESULTS

Serum TSH correlated with handgrip strength (HGS, r-coefficient = 0.233, p = .025), and total body bone mineral density (BMD) T-score values (r-coefficient = 0.321, p = .003). HGS measures were associated with BMD (r-coefficient = 0.415, p < .001), with bone mineral content (BMC, r-coefficient = 0.427, p < .001), and lean mass (r-coefficient = 0.326, p = .003). Women with low muscle strength, defined as HGS < 16 kg, had lower TSH levels than women with normal muscle strength (low vs. normal muscle strength, ANCOVA 1.13 ± 0.49 mU/L vs. 1.60 ± 0.83 mU/L, p = 0.024) independently of age, BMD, percentage of body fat or absolute lean mass. Multivariable linear regression analysis showed that HGS values were associated with TSH measurements (β-coefficient = 0.246, p = .014) and BMD T-score values (β-coefficient = 0.306, p = .002). All models were adjusted for age, body mass index (BMI), vitamin D, low-density lipoprotein cholesterol, current smoking, physical activity, and homeostasis model assessment of insulin resistance.

CONCLUSIONS

In this sample of postmenopausal women, lower serum TSH values, within normal range, were associated with lower muscle strength compared to higher normal TSH values. Further research is needed to elucidate the significance of our preliminary findings.

Biomarkers of frailty

Several biomarkers have been proposed to identify frailty, a multisystemic age-related syndrome. However, the complex pathophysiology and the absence of a consensus on a comprehensive and universal definition make it challenging to pinpoint a singular biomarker or set of biomarkers that conclusively characterize frailty. This review delves into the main laboratory biomarkers, placing special emphasis on those associated with various pathways closely tied to the frailty condition, such as inflammation, oxidative stress, mitochondrial dysfunction, metabolic and endocrine alterations and microRNA. Additionally, we provide a summary of different clinical biomarkers encompassing different tools that have been proposed to assess frailty. We further address various imaging biomarkers such as Dual Energy X-ray Absorptiometry, Bioelectrical Impedance analysis, Computed Tomography and Magnetic Resonance Imaging, Ultrasound and D3 Creatine dilution. Intervention to treat frailty, including non-pharmacological ones, especially those involving physical exercise and nutrition, and pharmacological interventions, that include those targeting specific mechanisms such as myostatin inhibitors, insulin sensitizer metformin and with special relevance for hormonal treatments are mentioned. We further address the levels of different biomarkers in monitoring the potential positive effects of some of these interventions. Despite the availability of numerous biomarkers, their performance and usefulness in the clinical arena are far from being satisfactory. Considering the multicausality of frailty, there is an increasing need to assess the role of sets of biomarkers and the combination between laboratory, clinical and image biomarkers, in terms of sensitivity, specificity and predictive values for the diagnosis and prognosis of the different outcomes of frailty to improve detection and monitoring of older people with frailty or at risk of developing it, being this a need in the everyday clinical practice.

Correlation of subclinical hypothyroidism with sarcopenia and its components in the Chinese older adults

OBJECTIVE

To identify the correlation of thyroid function and subclinical hypothyroidism (SCH) with sarcopenia and its components in the older Chinese adults.

METHODS

Older adults were recruited and divided into SCH group and non-SCH group. Free triiodothyronine (FT3), free thyroxine (FT4) and thyroid-stimulating hormone (TSH) were measured by electrochemiluminescence. Appendicular skeletal muscle mass (ASM) was measured, and skeletal muscle index (SMI) was further calculated. Grip strength was measured. Physical performance was graded by the Short Physical Performance Battery (SPPB) scores of the gait speed test, chair stand test and balance test.

RESULTS

Of the 240 older adults included, 48 (20.00%) presented with SCH. The prevalence of sarcopenia in SCH group was higher than that in non-SCH group (33.33% v.s. 18.75%). Grip strength was significantly lower in patients with SCH than those without sarcopenia. In terms of physical performance, 6-meter gait speed and SPPB score were lower in subjects with SCH than those without SCH, while 5 sit-to-stand movements was longer score in subjects with SCH than those without SCH. SCH was significantly correlated with sarcopenia, while FT3, FT4, and TSH levels were not. SCH was significantly correlated with low muscle strength and low muscle mass, but not with low physical performance. FT3 level was positively correlated with grip strength and SMI. TSH level was negatively correlated with grip strength, 6-meter gait speed, and SPPB score, but positively correlated with the time of 5 sit-to-stand movements.

CONCLUSION

SCH is a risk factor for sarcopenia in the older adults and correlated with low muscle strength and low muscle mass, but not with low physical performance. FT3, FT4 and TSH levels are associated with sarcopenia components, but not with sarcopenia.

Serum FT3/FT4, but not TSH is associated with handgrip strength in euthyroid U.S. population: evidence from NHANES

Objective

Although several studies have examined the relationship between thyroid function and muscle strength, their population primarily derived from Asian areas, and their results were controversial. Thus, this study aimed to explore the association between thyroid function and handgrip strength (HGS) in the U.S. population.

Methods

A total of 1,067 participants from NHANES were categorized into three different age groups including young (<45 years), middle (45~64 years), and old (≥65 years) age groups. Thyroid function was measured by the competitive binding immune-enzymatic assays, while HGS was examined by a trained evaluator using a dynamometer. The weighted multiple linear regression models were used to examine the association between thyroid function and handgrip strength. The restricted cubic splines were employed to explore the non-linear relationship between these two variables. All statistical analyses were performed using the SPSS version 20.0 and R software.

Results

After adjustment for potential covariates, FT3/FT4, but not TSH was positively associated with HGS in middle age group (β=0.091, t=2.428, P=0.016). The subgroup analysis by sex revealed that the positive association between FT3/FT4 and HGS was observed in the middle age group for both male and female participants (β=0.163, t=2.121, P=0.035; β=0.157, t=2.180, P=0.031). The RCS analysis showed a statistically significant non-linear association between FT3/FT4 and HGS in overall population (P for non-linear=0.026). After adjustment for covariates, men with low HGS had a significant lower FT3/FT4 than those without low HGS in old age group (P=0.013). There was a significant increase in TSH level for female participants with low HGS in old age group compared to those with normal HGS (P=0.048).

Conclusions

This study demonstrated FT3/FT4, but not TSH, was positively associated with HGS in middle age group, and the different association was observed in men in middle age group when participants were stratified by sex. Future longitudinal cohort study should be conducted to reveal the causal relationship between thyroid function and muscle strength.

Effect of thyroid-stimulating hormone suppression on quality of life in thyroid lobectomy patients: interim analysis of a multicenter, randomized controlled trial in low- to intermediate-risk thyroid cancer patients (MASTER study)

Purpose

Current clinical practices favor less or no thyroid-stimulating hormone (TSH) suppression for low- to intermediate-risk thyroid cancer patients who receive thyroid lobectomy. The association of TSH suppression on health-related quality of life (HR-QoL) in patients after thyroid lobectomy is not well studied. This study aimed to evaluate the effect of TSH suppression on patient HR-QoL after thyroid lobectomy.

Methods

This study included patients enrolled in an ongoing, multicenter, randomized controlled study investigating the effects of TSH suppression. Patients were randomized to either the low-TSH group (TSH target range, 0.3-1.99 µIU/mL) or the high-TSH group (TSH target range, 2.0-7.99 µIU/mL). The HR-QoL, hyperthyroidism symptom, and depression symptom questionnaires performed preoperatively and 2 weeks and 3 months postoperatively were evaluated.

Results

Total of 669 patients (low-TSH group, 340; high-TSH group, 329) were included. Although total HR-QoL score changes were not different between the 2 groups, the high-TSH group had a significantly higher score in the physical domain at postoperative 3 months (P = 0.046). The 2 groups did not have significant differences in hyperthyroidism and depression scores.

Conclusion

In the short-term postoperative period, the physical HR-QoL scores in thyroid lobectomy patients were better when they did not receive TSH suppression. This study suggests the importance of considering HR-QoL when setting TSH suppression targets in thyroid lobectomy patients.

Relationship between Euthyroidism and Muscle Mass and Strength: A Systematic Review

Thyroid hormones play a crucial role in skeletal muscle development, suggesting that thyroid function may influence muscle mass and muscle strength, which are both fundamental health-related indicators of several age-related consequences. However, whether there is a relationship between thyroid hormones, muscle mass, and muscle strength in individuals without thyroid dysfunctions is still unknown. Therefore, this systematic review aims to investigate whether thyroid hormones are related to muscle mass and strength parameters in euthyroid individuals. Three databases were searched (PubMed, Scopus, Web of Science) up to February 14, 2022, for peer-reviewed papers published in English. The search results were conducted independently by two different reviewers. The review included 13 studies with a total of 241,044 participants. All studies were observational: twelve studies measured thyroid stimulating hormone, ten and thirteen studies measured free triiodothyronine and free thyroxine, four studies analyzed the thyroid hormone ratio. The assessment methods for muscle mass were computed tomography, dual-energy X-ray absorptiometry and bioimpedance analysis, whereas hand dynamometer for muscle strength. Low levels within the normal range of free triiodothyronine, high levels within the normal range of free thyroxine, and lower thyroid hormone ratio may contribute to a reduced muscle function, which seems more evident in older males.

Exploring biomarkers of osteosarcopenia in older adults attending a frailty clinic

Osteosarcopenia is a new definitional approach that can increase the risk of falls and fractures in elderly compared with that of osteoporosis and sarcopenia alone. However, biomarkers for osteosarcopenia have not been well identified. Thus, we aimed to explore the biomarkers of osteosarcopenia, including bone, muscle, and geriatric markers. Outpatients attending a frailty clinic were enrolled in the study. Osteosarcopenia was defined as the coexistence of osteoporosis and sarcopenia. Osteoporosis was defined according to the criteria of the Japan Osteoporosis Society. Sarcopenia was defined according to the Asian Working Group for Sarcopenia consensus (2019). We selected 35 blood/serum pathological parameters, including bone, inflammation, nutritional, and aging markers for the study. Logistic regression analysis for osteosarcopenia was performed to explore the biomarkers of osteosarcopenia. Of the total 600 patients with a mean age of 76.6 years, 595 were enrolled in the registry during the study period. Logistic regression analysis for osteosarcopenia showed that elevated thyroid-stimulating hormone (TSH) (odds ratio [OR]:1.375; 95 % confidence interval [CI]: 1.092-1.731), bone-specific alkaline phosphatase (BAP) (OR: 1.059; 95 % CI: 1.002-1.120), and estimated glomerular filtration rate (eGFR) (OR: 1.029; 95 % CI: 1.007-1.053) increased the likelihood of osteosarcopenia. On the other hand, elevated 25-hydroxyvitamin D (25OHD) (OR: 0.905; 95 % CI: 0.841-0.974), blood urea nitrogen (BUN) (OR: 0.895; 95 % CI: 0.829-0.966) and K (OR: 0.241; 95 % CI: 0.081-0.717) decreased the likelihood of osteosarcopenia. It is worthwhile to examine these biomarkers for older adult outpatients attending a frailty clinic for screening osteosarcopenia. Further studies are needed to investigate the effects of other markers of bone metabolism.

Treating hypothyroidism is not always easy: When to treat subclinical hypothyroidism, TSH goals in the elderly, and alternatives to levothyroxine monotherapy

The majority of patients with hypothyroidism feel better when levothyroxine treatment restores thyroid-stimulating hormone (TSH) concentrations to normal. Increasingly, a significant minority of patients remain symptomatic and are dissatisfied with their treatment. Overzealous treatment of symptomatic patients with subclinical hypothyroidism may contribute to dissatisfaction among hypothyroidism patients, as potential hypothyroid symptoms in patients with minimal hypothyroidism rarely respond to treatment. Thyroid hormone prescriptions have increased by 30% in the United States in the last decade. The diagnosis of subclinical hypothyroidism should be confirmed by repeat thyroid function tests ideally obtained at least 2 months later, as 62% of elevated TSH levels may revert to normal spontaneously. Generally, treatment is not necessary unless the TSH exceeds 7.0-10 mIU/L. In double-blinded randomized controlled trials, treatment does not improve symptoms or cognitive function if the TSH is less than 10 mIU/L. While cardiovascular events may be reduced in patients under age 65 with subclinical hypothyroidism who are treated with levothyroxine, treatment may be harmful in elderly patients with subclinical hypothyroidism. TSH goals are age dependent, with a 97.5 percentile (upper limit of normal) of 3.6 mIU/L for patients under age 40, and 7.5 mIU/L for patients over age 80. In some hypothyroid patients who are dissatisfied with treatment, especially those with a polymorphism in type 2 deiodinase, combined treatment with levothyroxine and liothyronine may be preferred.

A Low Free T3 to Free T4 Ratio Is Associated with Sarcopenia in Euthyroid Patients with Type 2 Diabetes Mellitus

BACKGROUND

This research evaluated the link between normal thyroid hormone levels and sarcopenia in patients with type 2 diabetes mellitus (T2DM).

METHODS

This cross-sectional study enrolled 312 euthyroid patients with T2DM from Qilu Hospital of the Shandong University, China. Body composition, grip strength, and physical performance were assessed as per the 2019 consensus guidelines of the Asian Working Group for Sarcopenia. Binary logistic regression was used to examine the correlation between thyroid hormone levels and sarcopenia and its components.

RESULTS

The prevalence of sarcopenia was 26.9%. Following adjustments for potential confounders, a high-normal serum free triiodothyronine (FT3) level (odds ratio (OR) = 0.522, 95% confidence interval (CI): 0.304-0.895, P = 0.018), a low-normal serum free thyroxine (FT4) level (OR = 1.126, 95% CI: 1.009-1.258, P = 0.034), and a heightened FT3/FT4 ratio (OR = 0.923, 95% CI: 0.879-0.969, P = 0.001) were linked to a low prevalence of sarcopenia. Considering the components of sarcopenia, FT3 concentration was positively associated with muscle strength (OR = 0.525, 95% CI: 0.305-0.902, P = 0.020) and physical performance (OR = 0.443, 95% CI: 0.259-0.758, P = 0.003), while FT4 concentration was negatively linked to muscle mass (OR = 1.114, 95% CI: 1.009-1.232, P = 0.036). The FT3/FT4 ratio was positively linked to muscle mass (OR = 0.943, 95% CI: 0.905-0.981, P = 0.006), muscle strength (OR = 0.945, 95% CI: 0.901-0.992, P = 0.021), and physical performance (OR = 0.934, 95% CI: 0.894-0.975, P = 0.002). Nevertheless, thyroid-stimulating hormone concentration was not associated with sarcopenia.

CONCLUSION

A high FT3/FT4 ratio was significantly linked to a lowered risk of sarcopenia in euthyroid patients with T2DM.

Persisting neuroendocrine abnormalities and their association with physical impairment 5 years after critical illness

Background

Critical illness is hallmarked by neuroendocrine alterations throughout ICU stay. We investigated whether the neuroendocrine axes recover after ICU discharge and whether any residual abnormalities associate with physical functional impairments assessed 5 years after critical illness.

Methods

In this preplanned secondary analysis of the EPaNIC randomized controlled trial, we compared serum concentrations of hormones and binding proteins of the thyroid axis, the somatotropic axis and the adrenal axis in 436 adult patients who participated in the prospective 5-year clinical follow-up and who provided a blood sample with those in 50 demographically matched controls. We investigated independent associations between any long-term hormonal abnormalities and physical functional impairments (handgrip strength, 6-min walk distance, and physical health-related quality-of-life) with use of multivariable linear regression analyses.

Results

At 5-year follow-up, patients and controls had comparable serum concentrations of thyroid-stimulating hormone, thyroxine (T₄), triiodothyronine (T₃) and thyroxine-binding globulin, whereas patients had higher reverse T₃ (rT₃, p = 0.0002) and lower T₃/rT₃ (p = 0.0012) than controls. Patients had comparable concentrations of growth hormone, insulin-like growth factor-I (IGF-I) and IGF-binding protein 1 (IGFBP1), but higher IGFBP3 (p = 0.030) than controls. Total and free cortisol, cortisol-binding globulin and albumin concentrations were comparable for patients and controls. A lower T₃/rT₃ was independently associated with lower handgrip strength and shorter 6-min walk distance (p ≤ 0.036), and a higher IGFBP3 was independently associated with higher handgrip strength (p = 0.031).

Conclusions

Five years after ICU admission, most hormones and binding proteins of the thyroid, somatotropic and adrenal axes had recovered. The residual long-term abnormality within the thyroid axis was identified as risk factor for long-term physical impairment, whereas that within the somatotropic axis may be a compensatory protective response. Whether targeting of the residual abnormality in the thyroid axis may improve long-term physical outcome of the patients remains to be investigated.

Trial registration ClinicalTrials.gov: NCT00512122, registered on July 31, 2007 (https://www.clinicaltrials.gov/ct2/show/NCT00512122).

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03858-1.

Role of hormones in sarcopenia

Aging involves numerous changes in body composition that include a decrease in skeletal muscle mass. The gradual reduction in muscle mass is associated with a simultaneous decrease in muscle strength, which leads to reduced mobility, fragility and loss of independence. This process called sarcopenia is secondary to several factors such as sedentary lifestyle, inadequate nutrition, chronic inflammatory state and neurological alterations. However, the endocrine changes associated with aging seem to be of special importance in the development of sarcopenia. On one hand, advancing age is associated with a decreased secretion of the main hormones that stimulate skeletal muscle mass and function (growth hormone, insulin-like growth factor 1 (IGFI), testosterone and estradiol). On the other hand, the alteration of the IGF-I signaling along with decreased insulin sensitivity also have an important impact on myogenesis. Other hormones that decline with aging such as the adrenal-derived dehydroepiandrosterone, thyroid hormones and vitamin D seem to also be involved in sarcopenia. Adipokines released by adipose tissue show important changes during aging and can affect muscle physiology and metabolism. In addition, catabolic hormones such as cortisol and angiotensin II can accelerate aged-induced muscle atrophy, as they are involved in muscle wasting and their levels increase with age. The role played by all of these hormones and the possible use of some of them as therapeutic tools for treating sarcopenia will be discussed.

Different Relationships Between Thyrotropin and Muscle Strength According to Sex and Age in Euthyroid Koreans (The 6th Korea National Health and Nutritional Examination Survey 2014-2015)

Background: Changes in muscle mass and strength can be caused by multiple endocrine factors, including thyroid dysfunction. However, the relationship between thyroid function and muscle strength in euthyroid individuals is not clear. In the present study, we investigated the relationship between thyroid function and handgrip strength (HGS) in euthyroid Koreans, especially according to sex and age. Methods: This was a population-based, cross-sectional study from the 6th Korea National Health and Nutrition Examination Survey including 2894 Koreans (1487 men and 1407 women) aged ≥19 years. Serum thyrotropin (TSH) and free thyroxine (fT4) levels were measured. HGS was measured using a digital grip strength dynamometer. Results: Serum TSH level, but not serum fT4 level, was significantly associated with HGS in men, but neither TSH nor fT4 level was associated with HGS in women. Serum TSH showed a negative association with HGS in men aged <65 years (n = 1376; β = -0.566, p = 0.008), but a positive association in men aged ≥65 years (n = 111; β = 1.158, p = 0.010) after adjusting for confounders. HGS decreased as TSH tertile increased in men aged <65 years (p for trend = 0.010), but increased with TSH tertile in men aged ≥65 years (p for trend = 0.009) after adjusting for confounders. Odds ratios (ORs) for the lowest quartile of HGS increased in the highest tertile of TSH among men aged <65 years (OR = 1.657 [95% confidence interval {CI} 1.099-2.500], p = 0.006) and decreased in the highest tertile of TSH among men aged ≥65 years (OR = 0.176 [CI 0.032-0.966], p = 0.034) after adjusting for confounders. Conclusions: In euthyroid Koreans, serum TSH levels were significantly associated with HGS only in men and this relationship was found to depend significantly on age. These findings suggest that age has a distinct influence on the effect of even subtle change of thyroid function on muscle strength in men.

Effects of Thyroid Function on Phosphodiester Concentrations in Skeletal Muscle and Liver: An In Vivo NMRS Study

CONTEXT

Thyroid function is clinically evaluated by determination of circulating concentrations of thyrotropin (thyroid-stimulating hormone; TSH) and free thyroxine (fT4). However, a tissue-specific effector substrate of thyroid function is lacking. Energy-rich phosphorus-containing metabolites (PM) and phospholipids (PL) might be affected by thyroid hormone action and can be noninvasively measured by 31P nuclear magnetic resonance spectroscopy (NMRS).

OBJECTIVES

To measure the actions of peripheral thyroid hormones on PM and PL tissue concentrations.

DESIGN AND SETTING

A longitudinal, prospective pilot study was performed.

PARTICIPANTS

Nine patients with hyperthyroidism (HYPER) and 4 patients with hypothyroidism (HYPO) were studied at baseline and 3 months after treatment.

MAIN OUTCOME MEASURES

High-field 1H/31P NMRS was used to assess profiles of PM, PL, and flux through oxidative phosphorylase in liver and skeletal muscle, as well as ectopic tissue lipid content.

RESULTS

The concentrations of total skeletal muscle (m-) and hepatic (h-) phosphodiesters (PDE) and one of the PDE constituents, glycerophosphocholine (GPC), were lower in HYPER compared with HYPO (m-PDE: 1.4 ± 0.4 mM vs 7.4 ± 3.5 mM, P = 0.003; m-GPC: 0.9 ± 0.3 mM vs 6.7 ± 3.5 mM, P = 0.003; h-PDE: 4.4 ± 1.4 mM vs 9.9 ± 3.9 mM, P = 0.012; h-GPC: 2.2 ± 1.0 mM vs 5.1 ± 2.4 mM, P = 0.024). Both h-GPC (rho = -0.692, P = 0.018) and h-GPE (rho = -0.633, P = 0.036) correlated negatively with fT4. In muscle tissue, a strong negative association between m-GPC and fT4 (rho = -0.754, P = 0.003) was observed.

CONCLUSIONS

Thyroxine is closely negatively associated with the PDE concentrations in liver and skeletal muscle. Normalization of thyroid dysfunction resulted in a decline of PDE in hypothyroidism and an increase in hyperthyroidism. Thus, PDE might be a sensitive tool to estimate tissue-specific peripheral thyroid hormone action.

Lower hand grip strength in older adults with non-alcoholic fatty liver disease: a nationwide population-based study

Although both liver and muscle are metabolically active endocrine organs, and non-alcoholic fatty liver disease (NAFLD) and sarcopenia may share common pathogenic determinants, there have been few clinical studies of the relationship between NAFLD and muscle strength, especially in the elderly. We conducted a nationally representative population-based, cross-sectional study using data from the Korea National Health and Nutrition Examination Survey, which involved 1,897 men aged ≥50 years and 2,206 postmenopausal women. NAFLD was defined using the hepatic steatosis index (HSI) and low muscle strength was defined using the Korea-specific cut-off point of hand grip strength (HGS). Men and women with NAFLD had 7.3% and 7.9% lower HGS than controls, respectively. The odds ratios for low muscle strength in the presence of NAFLD were 2.51 in men and 2.34 in women. HSI inversely correlated with HGS in both men and women. Consistently, compared with men and women in the lowest HSI quartile, those in the highest quartile had 7.6% and 12.4% lower HGS, respectively, and were 5.63- and 3.58-times more likely to have low muscle strength, respectively. These results provide the first clinical evidence that NAFLD can be associated with muscular impairment in older adults, as demonstrated by lower muscle strength.

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.