Strength Is Associated With Sex Steroid Hormones In Males And Females Across The Lifespan

Sex-steroid hormones are typically anabolic, but whether they are predictive of strength among males and females with aging is not clear. PURPOSE: We determined whether sex-steroid hormone concentrations are associated with handgrip strength in young, middle-age, and old males and females. METHODS: 4,396 adults (2153 males, 2243 females) from the National Health and Nutrition Examination Survey (NHANES) (2013-2014) were categorized into three age groups: young (18-39y: 826 M, 849 F), middle-age (40-64y: 882 M, 925 F), and old (≥65y: 445 M and 469 F). Data extracted included dominant handgrip strength and concentrations of total testosterone (nmol/L), bioavailable testosterone (free androgen index, FAI%), and estradiol (pg/mL). RESULTS: Males were ~ 36% stronger than females (p < 0.01) across the age groups. Total testosterone was ~15X greater in males than females for all age groups, while bioavailable testosterone (FAI) was almost 30X greater in males. Total testosterone and FAI declined with age in both males and females. Estradiol was 4X greater in young females than males and declined with age 10-fold in females but no change in males. When averages of individuals in each 1-year age group were correlated, strength was associated with total testosterone in males (r = 0.45, p < 0.01) and females (r = 0.44, p < 0.01), with stronger associations for FAI in males (r = 0.80, p < 0.001) and females (r = 0.58, p < 0.001). Further, strength was predicted by estradiol concentrations in females (r = 0.81, p < 0.001), but not in males (r = -0.19, p = 0.14). When participants were separated into three age categories, total testosterone was not a significant indicator of handgrip strength for either sex at any age. However, FAI was associated with strength in middle-age (r = 0.15, p < 0.01) and old (r = 0.22, p < 0.01) adult males. For females, FAI was predictive of strength for young (r = 0.18, p < 0.01) and middle-age (r = 0.08, p < 0.05) adults, while estradiol was positively associated with strength for middle-age (r = 0.14, p < 0.01) and old females (r = 0.13, p < 0.01). CONCLUSIONS: These results indicate greater strength is best predicted by bioavailable testosterone in males and females, and estradiol in females. Thus, the relative contribution of sex-steroids varies across the lifespan and may be protective of strength decline with aging.