Testosterone is important throughout the life of any male.
It determines the development of male sexual characteristics during the development of the fetus. Without testosterone at the correct time of fetal development, the external male genitalia will not be developed or be underdeveloped.
During puberty, it is required for males to develop secondary sexual characteristics such as facial hair, pubic hair, enlargement of the penis and testes to adult size.
In cases where there is an infection of the testes, or trauma or injury to the testes or undescended testes before puberty, then males do not develop those secondary sexual characteristics.
It is required for the production of sperm by the testes. Testosterone is also required to maintain good bone health directly and indirectly as some testosterone is converted to estrogen which also helps to maintain bone health.
It also helps in maintaining muscle mass which indirectly improves body fat levels.
Testosterone can also affect mood and sex drive in males and may also affect erection.
There is also a growing body of evidence to suggest that testosterone is a factor to consider for cardiovascular health. A number of studies have shown that men who had coronary artery disease have lower levels of testosterone levels.
Low testosterone levels are also associated with increased risk of high-grade prostate cancer.