Review Article Testosterone Supplementation

Aging of humans is associated with a loss of muscle mass and function, and an increase in fat mass. Epidemiologic studies have demonstrated a correlation between bioavailable testosterone concentrations and fat-free mass and muscle strength. Testosterone replacement in older men with low testosterone levels increases fat-free mass and muscle strength, and decreases fat mass. However, we do not know whether testosterone replacement improves physical function and other health-related outcomes, or reduces the risk of disability, falls, or fractures in older men with low testosterone levels. The long-term risks and benefits of testosterone supplementation in older men are not known. AS humans grow older, their muscle mass decreases andfat mass increases (1–3). Aging-associated sarcopenia is an important public health problem that contributes to impaired physical function (4–6) and increased risk of falls, fractures (1,3), dependency, and death; therefore, anabolic interventions that reverse or prevent aging-related sarcope-nia are desirable. The rationale for the use of anabolic therapies, such as growth hormone, testosterone, or insulin-like growth factor (IGF)-I, is based on the premise that anabolic therapies, through alterations in intramuscular gene expression, increase muscle mass, and that increased muscle mass would translate into improved muscle performance. It is further assumed that improved muscle performance would improve measures of physical function and health-related outcomes, resulting in decreased physical dependency, improved health perceptions, decreased risk of falls and fractures, and mortality. Previous studies have demonstrated unequivocally that testosterone increases muscle mass (7– 17). Testosterone-induced increases in muscle mass are associated with improvements in maximal voluntary strength and leg power (18,19), but we do not know whether these improvements in muscle mass, muscle strength, and leg power translate into improvements in physical function or health-related outcomes. The effects of testosterone supplementation on quality of life, falls, fractures, or mortality are unknown