Changes in testosterone related to body composition in late midlife: Findings from the 1946 British birth cohort study

Objective Randomized trials in men with testosterone deficiency have provided evidence of short-term effects of testosterone therapy on muscle and fat mass but it is unclear whether this persists over a longer period or how testosterone affects women. We examined whether the midlife decline in testosterone relates to fat and lean mass in both sexes. Methods Data were collected from 440 men and 560 women participating in the 1946 British birth cohort study with testosterone measured at 53 and/or 60-64 years. Fat and appendicular lean mass were measured at 60-64 years using dual-energy X-ray absorptiometry. Results Mean free testosterone concentrations were lower at 60-64 than 53 years, by 26% in both sexes. At both ages testosterone was negatively associated with fat mass in men and positively associated in women. A larger decline in free testosterone was associated with higher fat mass in men but with lower fat mass among women. In contrast, declines in testosterone were not associated with lean mass in either sex. Conclusions Our findings suggest sex-divergent relationships between testosterone and fat mass and their distribution but do not support the hypothesis that midlife declines in testosterone lead to lower lean mass.