**2.14 Aging and androgens**

In aged men, there is a decade-by- decade decline in levels of androgens and an increase in bioavailable estrogens, with marked androgen deficiency most typically observed in the 6th–8th, even 9th, decade of life [33]. However, this shift in balance of androgens and estrogens can contribute to some of the adverse physiological effects observed in aging (termed "andropause"), such as reduced muscle mass, osteoporosis, and gynecomastia, as well as increase risk of prostate pathologies (from benign prostate hyperplasia to prostate carcinoma). The brain is also adversely affected by these changes and there are increased memory impairments, reduced libido/sex drive, and an increased risk for depression. As such, many men turn to androgen-based therapies to replace back androgens to ameliorate these symptoms. Clinical studies have demonstrated that administration of T to some aged men reinstates their affective and cognitive performance [34–36]. Despite the notion that marked androgen deficiency is most common after 60 years of age among men, men are often reported to use androgen replacement therapies even in their 4th decade, suggesting that some men may be particularly sensitive to decline or age-related changes in androgens, but this is not clear.
