**2.2 Patterns of androgens and effects in men**

Men experience a decade-by-decade decline in androgens, with marked androgen deficiency typically observed in the 6th–8th decade of life [1]. This shift in balance of androgens and estrogens can contribute to some of the adverse physiological effects observed in aging, such as reduced muscle mass, osteoporosis, and gynecomastia, as well as increase risk of prostate pathologies. The brain is also adversely affected by these changes as evidenced by memory impairments, reduced libido, and an increased risk for depression among some men. As such, many older men turn to androgen-based therapies to ameliorate these symptoms. However, androgen-based therapies may increase risk for unwanted proliferation in the prostate, as well as other physical and psychological side effects. Moreover, men are often reported to use androgen replacement therapies even in their 4th decade or earlier, suggesting that some men may be particularly sensitive to even modest androgen decline, or trophic effects of synthetic androgens (e.g. anabolic steroids).

#### **Figure 2.**

*Metabolism- depicts T metabolism via aromatase to estradiol and 5α-reductase and 3α-hydroxysteroid oxidoreductase to dihydrotestosterone and 3α-diol.*

A serious concern is that such treatments have potential to increase risk for prostate pathologies and other unwanted effects for brain function.
