Deeply involved in metabolism, testosterone packs quite a hefty punch – regulating, for example, the production of muscle and the breakdown of fat. Men with low testosterone are twice as likely to be insulin resistant—meaning their bodies struggle to regulate blood sugar—than those with normal levels of the hormone. Testosterone may help your body better respond to insulin and, in turn, head off metabolic health risks. Fitfluencers on TikTok tout testosterone as the ultimate metabolism hack, claiming more testosterone means more muscle, increased fat-burning, and an effortlessly speedier metabolism. Long recognized for its role as a sex hormone, mounting evidence underscores the importance of testosterone in the regulation of systemic metabolism in both male and female organisms. Total levels of testosterone in the body have been reported as 264 to 916 ng/dL (nanograms per deciliter) in non-obese European and American men age 19 to 39 years, while mean testosterone levels in adult men have been reported as 630 ng/dL. When testosterone levels are low, gonadotropin-releasing hormone (GnRH) is released by the hypothalamus, which in turn stimulates the pituitary gland to release FSH and LH. In androgen-deficient men with concomitant autoimmune thyroiditis, substitution therapy with testosterone leads to a decrease in thyroid autoantibody titres and an increase in thyroid's secretory capacity (SPINA-GT). Preliminary evidence suggests that low testosterone levels may be a risk factor for cognitive decline and possibly for dementia of the Alzheimer's type, a key argument in life extension medicine for the use of testosterone in anti-aging therapies. The brain is also affected by this sexual differentiation; the enzyme aromatase converts testosterone into estradiol that is responsible for masculinization of the brain in male mice. In addition, a continuous increase in vaginal sexual arousal may result in higher genital sensations and sexual appetitive behaviors. Women's level of testosterone is higher when measured pre-intercourse vs. pre-cuddling, as well as post-intercourse vs. post-cuddling. Men who watch sexually explicit films also report increased motivation and competitiveness, and decreased exhaustion. Here, we highlight key milestones in the history of testosterone's discovery and therapeutic applications. Testosterone is also metabolized to dihydrotestosterone-a potent, non-aromatizable AR agonist-through steroid 5α-reductases. The .gov means it’s official. Like other androsteroids, testosterone is manufactured industrially from microbial fermentation of plant cholesterol (e.g., from soybean oil). This also made it obvious that additional modifications on the synthesized testosterone could be made, i.e., esterification and alkylation. These independent partial syntheses of testosterone from a cholesterol base earned both Butenandt and Ruzicka the joint 1939 Nobel Prize in Chemistry. The chemical synthesis of testosterone from cholesterol was achieved in August that year by Butenandt and Hanisch. In women, mean levels of total testosterone have been reported to be 32.6 ng/dL. Like most hormones, testosterone is supplied to target tissues in the blood where much of it is transported bound to a specific plasma protein, sex hormone-binding globulin (SHBG). Like other steroid hormones, testosterone is derived from cholesterol (Figure 1).
