Testosterone, sexuality, and erectile function in aging men.

Human aging is associated with many changes, which resemble those seen with deficiencies of sex steroids or growth hormone and with cortisol excess. Among these are decreases in lean body mass (LBM) and muscle strength, loss of bone mineral, increase in body fat, and, in men, reduced libido and erectile function. Circulating total and free testosterone (T) decrease progressively with age in men, and these decreases correlate with observed changes in body composition and function. T is implicated in maintaining both male libido and erectile function, the latter effect possibly mediated by local increases in nerve nitric oxide (NO) synthase in the corpora cavernosa. Preliminary studies of T replacement in older men suggest improvements in LBM, fat, bone, libido, and erections, but more research needs to be done to better delineate benefits and potential risks before definitive recommendations can be made regarding T replacement in older men. Typical age-related changes in body composition and function include loss of lean body and muscle mass, decreased muscle strength (Kallman et al, 1990) and fitness (Fleg and Lakatta, 1988), and loss of functional capacity (Fried et al, 1998). There is also an increase in total fat mass and percent body fat (Shimokata et al, 1989) accompanied by insulin resistance and a higher risk of type 2 diabetes (Fink et al, 1983; Kohrt et al, 1993), increased low-density lipoprotein (LDL) cholesterol, triglycerides, and fatty acids (Obisesan et al, 1997). Other changes in metabolism include negative calcium balance leading to decreased bone density and osteoporotic fractures (Wark, 1996), decreased protein synthesis, slower healing, and impaired immune system function (Scordamaglia et al, 1991). Predictably, in aging men, there also occur decreased frequency of and desire for sexual activity and a reduction in the number and quality of erections (Kaiser et al, 1988; Helgason et al, 1996; Morley et al, 2000). Behavioral and psychological manifestations of aging also include slower problem solving, lapses of memory, and increasing incidence of dementing illness.