Male hypogonadism is a frequent and potentially undertreated condition. A number of longitudinal epidemiologic studies, including the Baltimore Longitudinal Study of Aging, the New Mexico Aging Process Study, and the Massachusetts Male Aging Study, have demonstrated age-related increases in the likelihood of developing hypogonadism. In addition to advancing age, increasing body mass index and/or type II diabetes mellitus may be associated with lower circulating androgen levels. Owing to the demographic trends toward increasing population age and life expectancy, together with the emerging pandemic of diabetes and recent trend toward an increasing prevalence of obesity in the United States, clinicians are likely to encounter increasing cases of hypogonadism in the near future.
Hypogonadism affects up to 4 million American men, yet only 5% of candidates receive treatment. Evidence suggests that low testosterone (T) and the attendant symptoms and signs of hypogonadism can be effectively treated using testosterone replacement therapy (TRT). This article will review the epidemiology of male hypogonadism. Subsequent articles will review (1) the etiology, pathophysiology, and diagnosis of male hypogonadism; and (2) the pharmacokinetics, efficacy, tolerability, and safety profiles of different forms of TRT, as well as required screening and monitoring tests prior to and during TRT.