Testosterone

(μmol/24hours)

Testosterone is the primary sex hormone and anabolic steroid in males. It is secreted primarily by the testicles of males and the ovaries of females, although small amounts are also secreted by the adrenal glands.

In men, testosterone plays a key role in the development of male reproductive tissues such as the testis and prostate as well as promoting secondary sexual characteristics such as increased muscle, bone mass, and the growth of body hair. In addition, testosterone is essential for health and well-being as well as the prevention of osteoporosis.

On average, in adult males, levels of testosterone are about 7–8 times as great as in adult females, but, as the metabolic consumption of testosterone in males is greater, the daily production is about 20 times greater in men. Females are also more sensitive to the hormone.

Abnormalities. Disorders or diseases caused or related.

Recent studies have shown conflicting results concerning the importance of testosterone in maintaining cardiovascular health. Nevertheless, maintaining normal testosterone levels in elderly men has been shown to improve many parameters that are thought to reduce cardiovascular disease risk, such as increased lean body mass, decreased visceral fat mass, decreased total cholesterol, and glycaemic control.

When testosterone levels are low, gonadotropin-releasing hormone (GnRH) is released by the  hypothalamus, which in turn stimulates the pituitary gland to release FSH and LH. These latter two hormones stimulate the testis to synthesize testosterone. Finally, increasing levels of testosterone through a negative feedback loop act on the hypothalamus and pituitary to inhibit the release of GnRH and FSH/LH, respectively.

Factors affecting low levels of testosterone include:

Age: Testosterone levels gradually reduce as men age. This effect is sometimes referred to as andropause or late-onset hypogonadism.

Nutrients: Zinc deficiency lowers testosterone levels but over-supplementation has no effect on serum testosterone. There is limited evidence that low-fat diets may reduce total and free testosterone levels in men.

Drugs: Natural or man-made antiandrogens including spearmint tea reduce testosterone levels. Licorice can decrease the production of testosterone and this effect is greater in females.

Insufficient levels of testosterone in men may lead to abnormalities including frailty and bone loss.

Factors affecting the elevation of testosterone levels include:

Exercise: Resistance training increases testosterone levels, however, in older men, that increase can be avoided by protein ingestion. Endurance training in men may lead to lower testosterone levels.

Nutrients: The secosteroid vitamin D in levels of 400–1000 IU/d (10–25 µg/d) raises testosterone levels.

Weight loss: Reduction in weight may result in an increase in testosterone levels. Fat cells synthesize the enzyme aromatase, which converts testosterone, the male sex hormone, into estradiol, the female sex hormone. However, no clear association between body mass index and testosterone levels has been found.

Sleep: REM sleep increases nocturnal testosterone levels.

Behavior: Dominance challenges can, in some cases, stimulate increased testosterone release in men.

Men whose testosterone levels are slightly above average are less likely to have high blood pressure, less likely to experience a heart attack, less likely to be obese, and less likely to rate their own health as fair or poor. However, high-testosterone men are more likely to report one or more injuries, more likely to consume five or more alcoholic drinks in a day, more likely to have had a sexually transmitted infection, and more likely to smoke.

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