Can lower testosterone reduce muscle mass and skeletal-muscle glucose disposal?

Lower testosterone is credibly linked to loss of lean mass in older men, but the proposed downstream effect on skeletal-muscle glucose disposal is biologically plausible rather than directly proven.

Clinical and body-composition evidence

• In a 6-month randomized placebo-controlled trial of men aged 60–78 with low-normal bioavailable testosterone, testosterone replacement increased lean body mass by approximately 1.9 kg versus placebo and reduced fat mass by about 1.2 kg. Comparable trials, including in men with type 2 diabetes and hypogonadism, also report lean-mass gains.
• These findings support testosterone as a contributor to maintaining muscle mass. For a 70-year-old man, low testosterone could therefore be one contributor to sarcopenia, although trial evidence does not specifically quantify the effect of naturally low testosterone in those aged ≥70.

Glucose disposal and metabolic implications

• Skeletal muscle is a major insulin-responsive glucose-consuming tissue; less muscle tissue could reduce total insulin-stimulated glucose uptake capacity.
• However, testosterone-induced increases in lean mass have not consistently improved clamp-measured insulin-stimulated glucose disposal. In the key older-men trial, lean-mass gain did not improve clamp-derived disposal. Among hypogonadal men with diabetes, one study reported a 32% increase in clamp glucose infusion rate, while another found improved lean mass without improved insulin sensitivity.
• Higher endogenous testosterone has been associated with better clamp-measured insulin sensitivity, but attenuation after BMI adjustment indicates that adiposity is an important linked explanation.

Mechanistic context

• Lower testosterone is associated with greater fat mass and, in limited observational mechanistic data, reduced skeletal-muscle mitochondrial-function markers alongside lower insulin sensitivity. These pathways may contribute independently of, or alongside, muscle mass.

Bottom line

• Lower testosterone can contribute to reduced muscle mass; reduced skeletal-muscle glucose disposal is a credible consequence but is not established as a direct muscle-mass-mediated effect.