The relationship between obesity, metabolic syndrome, and androgen deficiency remains unclear because of the complex mechanisms involved in this association. Impairment of hypothalamic-pituitary function by decreased LH pulse amplitude, inhibitory effects of estrogen at the
hypothalamus and pituitary, and the effects of leptin, ghrelin, and resistin, both centrally and on testicular Leydig cells, may explain lower testosterone level in obese males. 24,25 Recent studies have suggested a possible increased risk of CV events among groups of men prescribed TRT. 26,27 However, other studies demonstrate beneficial effects of TRT on CVD risk factors, and research over several decades suggests a strong beneficial relationship between normal T and CV health.26 The evidence to suggest that TRT increases CV morbidity and mortality risks is poor, 28 but FDA is investigating the link between TRT and adverse CV outcomes. 29
Testosterone replacement therapy is recommended for symptomatic men with androgen deficiency to induce or maintain secondary sex characteristics and improve their sexual function, sense of well-being, muscle mass, strength, and bone mineral density. In a recent study supported by the National Institutes of Health (NIH) in men aged 65 years, increasing serum testosterone levels to mid-normal range for 1 year was associated with a moderate benefit in sexual function and improved mood, but there was no significant benefit in vitality (as measured by a fatigue scale) or walking distance. 28 In the NIH study, 4 men in the testosterone group and 1 in the placebo group received a diagnosis of PCa during or within the subsequent year of treatment, but the sample size was inadequate to reliably assess the effect of testosterone
on the risk of PCa. 28
With increasing direct-to-consumer marketing of branded pharmaceutical products in the U.S., there is widening interest in testosterone levels and hypogonadism symptoms in middle-aged and older men. Indeed, 2.3 million patients received a prescription for testosterone in 2013, up from 1.3 million in 2010. 29,30 This change has become important because whereas TRT is standard therapy in symptomatic hypogonadal men, it has long been considered taboo for men with a history of PCa, regardless of disease status. Transdermal testosterone is contraindicated in men with carcinoma of the breast or known or suspected carcinoma of the prostate, according to the package insert. 31 Androgens are contraindicated in men with known or suspected carcinoma of the prostate or breast, according to the testosterone cypionate injection package insert. 32 Although TRT may increase serum PSA levels in some men, it often remains within clinically acceptable ranges and has not been shown to increase the risk for PCa. A recent observation from 3 registries of more than 1,000 hypogonadal men receiving TRT for up to 17 years concluded that TRT does not increase the risk for PCa. 33
Prostate cancer encompasses a heterogeneous collection of androgen-dependent and independent cells. Androgens have been known to play an important role in PCa biology, but this relationship is more complex than the traditional view that androgens stimulate PCa growth. More than 7 decades ago, Huggins and colleagues showed that disseminated PCa was inhibited by eliminating androgens by castration and activated by androgen injections. 34 Recently, the androgen hypothesis and the relationship of testosterone to PCa has been more clearly defined. Although it has been established that effective suppression of serum T levels with surgical or chemical castration remains an essential strategy in the management of advanced PCa, the assertion that testosterone causes growth of PCa has been challenged. 35,36