Total testosterone is not associated with lean mass or handgrip strength in pre-menopausal females: findings from the NHANES

Testosterone is a naturally occurring hormone that has been positively associated with lean mass and strength in males. Whether endogenous testosterone is related to lean mass and strength in females is unknown. Objective To examine the relationship between endogenous testosterone concentration and lean mass and handgrip strength in healthy, pre-menopausal females. Methods Secondary data from the 2013-2014 National Health and Nutrition Examination Survey (NHANES)were used. Females were aged 18-40 (n=753, age 30 ± 6 yr, mean ± SD) and pre-menopausal. Multivariate linear regression models were used to examine associations between total testosterone, height-adjusted lean mass and handgrip strength. Results Mean ± SD testosterone concentration was 1.0 ± 0.6 nmol·L -1 and mean free androgen index (FAI) was 0.02 ± 0.02. Mean fat-free mass index (FFMI) was 16.4 ± 3.0 kg·m -2 and mean handgrip strength was 61.7 ± 10.5 kg. In females, testosterone was not associated with FFMI (β=0.08; 95%CI: −0.02, 0.18; p=0.11) or handgrip strength (β=0.03; 95%CI: −0.11, 0.17; p=0.67) in a statistically significant manner. Conversely, FAI was positively associated with FFMI (β=0.17; 95%CI: 0.01, 0.33; p=0.04 ) but not handgrip strength (β=0.19; 95%CI: −0.02, 0.21; p=0.10 ). Conclusions These findings indicate that FAI, but not total testosterone, is associated with FFMI in females. The small coefficients however suggest that FAI only accounts for a minor proportion of the variance in FFMI, highlighting the complexity of the regulation of lean mass in female physiology. FAI nor total testosterone are associated with handgrip strength in females when testosterone concentrations are not altered pharmacologically.