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Testosterone is the hormone of male sexual desire. Although women's bodies also make tiny amounts of testosterone, this androgen hormone is most commonly associated with the sexual characteristics that make men identifiable as men. These characteristics are body hair, aggressiveness, memory skills related to sex and competitive activities, and skin texture, with, of course, the size of the sexual organ and the interest and ability to use it.

"Lard Butt" Is the Enemy of Testosterone
Low testosterone is a common condition among men who have passed the age of 40. The single most important factor in most men's testosterone levels is fat mass. You may not know that fat cells do not just store fat. They also make hormones.
In men, body fat, especially buttocks fat, creates an enzyme called aromatase. This is an enzyme that can transform the male sex hormone testosterone into the female sex hormone estrogen. When men lounge around and stuff themselves while watching TV, they encourage the growth of body fat that can rob their bodies of testosterone.
Testosterone is essential for a man's sex drive. The areas of the brain that direct sex-seeking behavior are stimulated by testosterone. A burst of testosterone into the bloodstream has some astonishing effects when it reaches the brain.
- Testosterone increases the male brain's ability to interpret spatial relationships. This ability helps men find the right parts.
- Testosterone powers short-term memory in men. If a man needs to remember the right sweet nothing to whisper into his lover's ear, testosterone will help him do it.
- Testosterone also increases activity and aggression. Men who have higher testosterone levels are more inclined to seek new partners — and to fend off the competition.
In situations in which there is a possibility of sexual intercourse, the testes are triggered to release testosterone. Straight men get a boost in their testosterone just by talking to women. (It is not known whether gay men get a boost in testosterone levels by talking with other men at the moment.)
Straight men get a boost in their testosterone levels just by talking to women to whom they are not partnered, even if the conversation is by phone, in fact — so effective is this hormone. Both straight and gay men, it is interesting to note, experience lower levels of testosterone after spending 1 to 3 years in a stable relationship.
Testosterone Essential to Penis Size, Testicle Size, and Fertility
Testosterone is essential to male fertility, as it enables the testes to transform Leydig cells into sperm cells. It fuels the growth of the lining of the prostate, which releases seminal fluid to mix with sperm to become semen. And testosterone stimulates the growth and maintenance of penis and testicular tissue that keeps them their normal size.
There is absolutely no doubt that testosterone is essential for sex for men. Millions of men report a renaissance in their sex lives when they start taking injected testosterone or a testosterone patch. But maintaining a man's sex life is not the most urgent medical reason for treating low-T.
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- Metter EJ, Tobin JD, Pearson J, Blackman MR, Longitudinal effects of aging on serum total and free testosterone levels in healthy men. Baltimore Longitudinal Study of Aging. J Clin Endocrinol Metab. 2001. 86:724–731,
- Photo courtesy of linden_tea on Flickr: www.flickr.com/photos/linden_tea/4564568606/