Testosterone is the principal male sex hormone, but contrary to popular belief, testosterone is not uniquely male. While males produce testosterone in the testes, females produce small amounts of testosterone in the ovaries. Testosterone is necessary for various sexual functions, as well as protein synthesis and muscular development.
Testosterone Development
Males begin to develop testosterone while still fetuses. Testosterone is responsible for development of the male genitalia in the womb, and is necessary for the further growth of the penis and testes during puberty. Secondary sex characteristics such as the growth of facial hair, pubic hair and a deepening voice also depend on testosterone.
Growth of Body
Testosterone helps males grow taller and more muscular during puberty. Testosterone also helps maintain muscle and bone strength in adulthood, and can have an effect on hair growth.
Sex Drive
Testosterone assists the testes in producing sperm, and helps keep a man's sex drive alive and well. If levels of testosterone in the body are low, men can experience a decreased desire to have sex, low sperm count, impotence or erectile dysfunction, as well as increased breast size. Not all sexual problems, however, are due to lack of testosterone. For example, circulation problems can be just as responsible for erectile dysfunction as testosterone deficiency.
Testosterone Deficiency
In addition to sexual difficulties, a testosterone deficiency can cause hot flashes, irritability and depression, while extreme cases can result in loss of body hair, muscle mass, shrunken testes and brittle bones.
Mental Function
Though results are not conclusive, a study in the January 2008 issue of Harvard Men's Health Watch hypothesized that testosterone might promote mental health. It might be a coincidence that testosterone levels begin to drop just as memory begins to fail, but Harvard Men's Health Watch states that dropping levels of testosterone during aging might be partially responsible for memory loss and failing mental function.
Supplementing Testosterone
People substitute testosterone for various reasons--to increase or rejuvenate interest in sex, improve erectile function, increase muscle mass and strengthen muscles. Some athletes use testosterone injections--often illegally-- to increase energy to train harder and recover more quickly. Both men and women can partake in hormone replacement therapy, but the practice is controversial.
The long-term effects of testosterone supplements are not yet known. According to the National Institute on Aging, steroid supplements can possibly cause prostate cancer, thicken blood or increase chances or stroke.
