Testosterone

Last Updated: August 19 2022

Testosterone is the best-known androgen (male hormone), but females produce it too. In both sexes, low testosterone can reduce libido and cause fat gain, muscle loss, and bone loss.

Overview

Testosterone is a hormone produced primarily in the testes in men and the ovaries in women. Testosterone is connected to sexual development, muscle building, fat loss, some aspects of cognition, and hair loss.[1]

Your testosterone levels may not tell the whole story of how testosterone is functioning in your body. Total testosterone can be divided into three categories.[2]

  • Tightly bound testosterone: About two-thirds of the testosterone in your blood is bound to sex hormone binding globulin (SHBG). It is not readily available for use by your body.
  • Loosely bound testosterone: About one-third of the testosterone in your blood is weakly bound to albumin. Once the bond is broken, the testosterone circulates as free testosterone in your body.
  • Free testosterone: A small percentage of the testosterone in your blood (1–4%, as a rule) floats around freely. Your body can readily use it, and the enzyme 5-alpha-reductase can convert it to dihydrotestosterone (DHT), a very potent androgen.

Together, your loosely bound and free testosterone compose your bioavailable testosterone, which has a greater impact on your health than your total testosterone.

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