Testosterone is a sex hormone that plays important roles in the body. In men, it’s thought to regulate sex drive (libido), bone mass, fat distribution, muscle mass and strength, and the production of red blood cells and sperm. A small amount of circulating testosterone is converted to estradiol, a form of estrogen. As men age, they often make less testosterone, and so they produce less estradiol as well. Thus, changes often attributed to testosterone deficiency might be partly or entirely due to the accompanying decline in estradiol.
It was first used as a clinical drug as early as 1937, but with little understanding of its mechanisms. The hormone is now widely prescribed to men whose bodies naturally produce low levels. But the levels at which testosterone deficiency become medically relevant still aren’t well understood. It normal production varies widely in men, so it’s difficult to know what levels have medical significance. The hormone’s mechanisms of action are also unclear.
What is testosterone?
It is the hormone responsible for the development of male sexual characteristics. Hormones are chemical messengers that trigger necessary changes in the body. Females also produce it, usually in smaller amounts.
It is a type of androgen produced primarily by the testicles in cells called the Leydig cells.
In men, it is thought to regulate a number of functions alongside sperm production. These include:
- sex drive
- bone mass
- fat distribution
- muscle size and strength
- red blood cell production
Without adequate amounts of testosterone, men become infertile. This is because it assists the development of mature sperm.
Despite being a male sex hormone, it also contributes to sex drive, bone density, and muscle strength in women. However, an excess of it can also cause women to experience male pattern baldness and infertility.