- Testosterone is a potent steroid hormone belonging to the class of androgens, which are primarily responsible for the development and maintenance of male reproductive tissues and secondary sexual characteristics.
- Although it is commonly associated with male physiology, testosterone also plays important roles in females, albeit at lower concentrations.
- In males, testosterone is predominantly produced by the Leydig cells of the testes, while in females, it is produced in smaller amounts by the ovaries and the adrenal glands in both sexes.
- Testosterone synthesis is regulated by the hypothalamic-pituitary-gonadal (HPG) axis. The hypothalamus secretes gonadotropin-releasing hormone (GnRH) in a pulsatile manner, which stimulates the anterior pituitary to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH acts on Leydig cells to promote the conversion of cholesterol into testosterone. Once released into the bloodstream, testosterone exerts its effects by binding to androgen receptors in various tissues or by being converted into dihydrotestosterone (DHT) or estradiol by the enzymes 5α-reductase and aromatase, respectively.
- In males, testosterone is essential for the development of the male reproductive system during embryogenesis, including the formation of the penis, scrotum, and prostate gland. During puberty, a surge in testosterone levels triggers the development of secondary sexual characteristics, such as increased muscle mass, deepening of the voice, facial and body hair growth, enlargement of the testes and penis, and increased libido. Throughout adulthood, testosterone helps maintain sperm production (spermatogenesis), bone density, red blood cell production, mood, and overall vitality.
- In females, although testosterone levels are much lower, the hormone still plays a vital role in regulating libido, bone health, and muscle strength, and it serves as a precursor for the synthesis of estrogens. In both sexes, an appropriate balance of testosterone is necessary for metabolic health, mood regulation, and cognitive function.
- Testosterone levels vary naturally with age, time of day, and individual physiology. In males, levels peak in early adulthood and gradually decline with age, a process sometimes referred to as andropause. Abnormally low testosterone levels (hypogonadism) can result in fatigue, reduced muscle mass, depression, erectile dysfunction, and infertility. Conversely, excess testosterone, whether endogenous or from external sources (such as anabolic steroid abuse), can lead to aggression, acne, hair loss, infertility, liver damage, and cardiovascular risks.
- Medical interventions involving testosterone include testosterone replacement therapy (TRT) for men with clinically diagnosed hypogonadism, and in some cases, testosterone may be used to support transitioning individuals in gender-affirming care. Monitoring and managing testosterone levels is also crucial in the context of certain conditions like prostate cancer, where androgens can promote tumor growth.
