Yeqing Gu1, Ge Meng2, Hongmei Wu1, Qing Zhang3, Li Liu3, Xue Bao1, Yawen Wang1, Shunming Zhang1, Shaomei Sun3, Xing Wang3, Ming Zhou3, Qiyu Jia3, Kun Song3, Kaijun Niu4. 1. Nutritional Epidemiology Institute and School of Public Health, Tianjin Medical University, Tianjin, China. 2. Nutritional Epidemiology Institute and School of Public Health, Tianjin Medical University, Tianjin, China; Department of Toxicology and Sanitary Chemistry, School of Public Health, Tianjin Medical University, Tianjin, China. 3. Health Management Centre, Tianjin Medical University General Hospital, Tianjin, China. 4. Nutritional Epidemiology Institute and School of Public Health, Tianjin Medical University, Tianjin, China; Health Management Centre, Tianjin Medical University General Hospital, Tianjin, China; Tianjin Key Laboratory of Environment, Nutrition and Public Health, Tianjin, China; Center for International Collaborative Research on Environment, Nutrition and Public Health, Tianjin, China. Electronic address: nkj0809@gmail.com.
Abstract
OBJECTIVES: Thyroid hormones (THs) play a critical role in skeletal muscle function, such as protein synthesis and energy metabolism, suggesting that thyroid function may be involved in the decline of muscle strength. Studies regarding the long-term effects of THs on muscle strength are limited. Therefore, this large-scale longitudinal study aimed to explore how TH levels were associated with handgrip strength (HGS) among middle-aged and older euthyroid adults. DESIGN: Longitudinal population-based cohort study (approximately 4-year follow-up period, median: 3.0 years). SETTING: The Tianjin Chronic Low-grade Systemic Inflammation and Health Cohort Study, Tianjin, China. PARTICIPANTS: A total of 2152 participants were enrolled, and annual measures were conducted in this longitudinal study. MEASURES: Chemiluminescence immunoassay was used to measure free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH). HGS was measured using a handheld digital dynamometer. Multiple linear regression analysis was used to evaluate the association between THs, FT3/FT4 ratio, TSH levels, and annual change in HGS and weight-adjusted HGS. RESULTS: After adjusting for multiple confounding factors, significant associations between FT3 levels, FT3/FT4 ratio, and annual change in HGS [standard regression coefficient (SRC) = 0.073, P < .01, and and SRC = 0.059, P = .01, respectively] were observed. However, no significant difference was observed between FT4, TSH, and annual change in HGS (SRC = 0.021, P = .34; and SRC = -0.017, P = .44, respectively). Similar associations between FT3, FT4, FT3/FT4 ratio, TSH, and weight-adjusted HGS were observed. CONCLUSIONS AND IMPLICATIONS: This longitudinal study is the first to demonstrate that high-normal FT3 levels and higher FT3/FT4 ratios significantly predict annual change in HGS and weight-adjusted HGS and that FT4 and TSH levels are not associated with HGS among middle-aged and older euthyroid subjects. The findings suggest that new therapeutic approaches aimed at FT3 levels and FT3/FT4 ratios may be proposed to maintain muscle strength.
OBJECTIVES: Thyroid hormones (THs) play a critical role in skeletal muscle function, such as protein synthesis and energy metabolism, suggesting that thyroid function may be involved in the decline of muscle strength. Studies regarding the long-term effects of THs on muscle strength are limited. Therefore, this large-scale longitudinal study aimed to explore how TH levels were associated with handgrip strength (HGS) among middle-aged and older euthyroid adults. DESIGN: Longitudinal population-based cohort study (approximately 4-year follow-up period, median: 3.0 years). SETTING: The Tianjin Chronic Low-grade Systemic Inflammation and Health Cohort Study, Tianjin, China. PARTICIPANTS: A total of 2152 participants were enrolled, and annual measures were conducted in this longitudinal study. MEASURES: Chemiluminescence immunoassay was used to measure free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH). HGS was measured using a handheld digital dynamometer. Multiple linear regression analysis was used to evaluate the association between THs, FT3/FT4 ratio, TSH levels, and annual change in HGS and weight-adjusted HGS. RESULTS: After adjusting for multiple confounding factors, significant associations between FT3 levels, FT3/FT4 ratio, and annual change in HGS [standard regression coefficient (SRC) = 0.073, P < .01, and and SRC = 0.059, P = .01, respectively] were observed. However, no significant difference was observed between FT4, TSH, and annual change in HGS (SRC = 0.021, P = .34; and SRC = -0.017, P = .44, respectively). Similar associations between FT3, FT4, FT3/FT4 ratio, TSH, and weight-adjusted HGS were observed. CONCLUSIONS AND IMPLICATIONS: This longitudinal study is the first to demonstrate that high-normal FT3 levels and higher FT3/FT4 ratios significantly predict annual change in HGS and weight-adjusted HGS and that FT4 and TSH levels are not associated with HGS among middle-aged and older euthyroid subjects. The findings suggest that new therapeutic approaches aimed at FT3 levels and FT3/FT4 ratios may be proposed to maintain muscle strength.