Associations Between Female Sex Hormones and Skeletal Muscle Ageing: The Baltimore Longitudinal Study of Aging
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Background
To date, most research investigating the influence of circulating sex hormones on ageing female skeletal muscle has been cross-sectional and focused only on dichotomised young and old, or pre-versus post-menopausal groups. This excludes an important transitional period from high to low circulating oestrogen. Using secondary data from the Baltimore Longitudinal Study of Aging, this study aimed to investigate cross-sectional and longitudinal associations between circulating sex hormones and skeletal muscle mass and function across a continuum of ages.
Methods
Multiple and binomial linear regression was used to map cross-sectional (n=319) and longitudinal (n=83) associations between circulating sex hormones (oestradiol (E2), free oestradiol index (FEI), free (TT) and bioavailable testosterone (BioT), testosterone/oestradiol ratio (TT/E2)) and skeletal muscle mass and function in healthy females. Cross-sectional models analysed females across an ageing continuum (24-89 years) and longitudinal associations were tested across 4-6 years of ageing in females over 50 years old. Models were adjusted for age, height, physical activity, comorbidities, and ethnicity.
Results
Cross-sectionally, serum E2 and FEI were positively associated with relative appendicular lean mass (ALM; β=0.28 and 0.20, respectively, p <0.05) and thigh muscle percentage (β=0.19 and 0.15, respectively, p <0.05). E2 and FEI were negatively associated with total body fat percentage (β=-0.30 and -0.21, respectively, p <0.05). BioT was positively associated with absolute ALM (β=0.13, p <0.05) and total body fat percentage (β=0.18, p <0.05). TT was negatively associated with total body fat percentage (β=-0.14, p <0.05). The TT/E2 ratio was negatively associated with thigh muscle CSA (β=-0.08, p <0.05) and hamstring strength (β=-0.12, p <0.05). Across 4-6 years, a decrease in E2 and FEI were associated with a decrease in ALM (β=0.29 and 0.42, respectively, p <0.05), and decrease in FEI was associated with a decrease in handgrip strength (β=0.17, p <0.05). A decrease in TT and BioT were associated with an increase in relative ALM (β=-0.25 for both, p <0.05) and relative quadriceps strength (β=-0.12 and -0.27, respectively, p <0.05)
Conclusion
This study demonstrates novel associations between sex hormone levels and skeletal muscle in females across a wide continuum of ages. We also demonstrate that longitudinal fluctuations in circulating sex hormones must be considered to gain a comprehensive understanding of female muscle ageing.
