Testosterone is the principal male sex hormone (androgen) secreted by the testes, starting at puberty. (In women, the adrenal glands and ovaries produce small amounts.) Levels begin to plateau at around age 40, and gradually decrease to one-fifth the peak level at age 80.
- To evaluate male infertility or sexual dysfunction
- To help determine the cause of hypogonadism (decreased testosterone secretion)
- To aid in the evaluation of virilization (the development of male characteristics such as male-type baldness) in women
It is quite common for men entering their late 40s and early 50s to experience a loss of sex drive, impotence and depression. This decline is due to a natural reduction in testosterone production.
By the time a man reaches 40, his testosterone will be approximately 1/2 what it was in his twenties. When a man reaches 50 years old, his testosterone level will be 1/3 of its peak – at 60 it will be 1/4 or less. For men of any age the inability to build muscle may indicate low testosterone levels.