The Effect of Sex Steroid Replacement Therapy in the Hypogonadism and Transgender Active-Duty Population

The Endocrine Society defines male hypogonadism as a clinical syndrome that results from failure of the testis to produce physiological levels of testosterone (androgen deficiency) and the normal number of spermatozoa caused by disruption of one or more levels of the hypothalamic-pituitary-gonadal (HPG) axis. It is characterized by low serum testosterone/ high LH/high FSH concentrations (primary hypogonadism) or low testosterone/low LH/low FSH (secondary hypogonadism). The main constellation of signs and symptoms may include erectile dysfunction , decreased libido and volume of ejaculation, decreased lean body mass with increased body fat, loss of body and facial hair, weakness, fatigue, anemia and decreased bone density. There is only little data from large cross-sectional studies that address the impact of hypogonadism on morbidity. However, some small studies have concluded that testosterone deficiency could lead to a higher prevalence of depression, osteoporosis, fracture and frailty . Hypogonadism defined as serum total testosterone level \<300 ng/dl has been shown to be related to decreased bone mineral density (BMD). Further review of the literature found various epidemiological studies in men that showed the associations between testosterone and estradiol levels and BMD. They found that estrogen has a major role in regulating bone resorption but both estrogen and testosterone play a role in maintaining bone formation. A recent published trial in 2017 also showed that testosterone replacement therapy in older men was associated with significant greater improvements in stair-climbing power, muscle mass and power. Similar studies found that deficiency of testosterone would lead to decrease in lean mass, muscle size and strength. Given that these two sex steroid hormones, testosterone and estrogen, play an important role in men and women, respectively, we also study their long-term effects in the transgender population once they were started on the opposite gender hormone and lack of their own endogenous production.