Males need adequate levels of the hormone testosterone throughout development and adulthood to produce sperm and to maintain typical male characteristics. Testosterone levels vary widely at different points in development, and even in adult men, factors like age and time of day can significantly affect testosterone secretion. Too little testosterone results in a condition called hypogonadism, while men generally do not show any effects of elevated testosterone.
Measurement
The American Association of Clinical Endocrinologists recommends measuring testosterone levels in the morning because levels peak in the morning and then decline throughout the day. Most testosterone circulates tightly bound to a molecule called sex hormone binding globulin (SHBG). While bound to SHBG, testosterone cannot act on cells and is considered biologically unavailable, in contrast to free testosterone. Routine blood tests can measure total testosterone, but the American Association of Clinical Endocrinologists advocates for determination of both total and free testosterone levels to accurately assess the amount that is biologically available.
Normal Levels
A simple blood test in a laboratory can measure the total amount of testosterone circulating in the blood. According to Harvard Health, levels of testosterone can vary widely, with levels between 270 to 1,070 nanograms per deciliter of blood (ng/dL) falling in the "normal" range. More complicated tests can determine the amount of biologically active testosterone. Harvard Health cites a study showing normal men aged 40 to 69 had between 69 and 499 ng/dL of biologically available testosterone.
Production
An average adult man produces 4 to 10 mg of testosterone per day in his testes, according to "Endocrinology: An Integrated Approach." The testicular contribution accounts for over 95 percent of all circulating testosterone. The remaining 5 percent comes from the conversion of weaker adrenal androgens into testosterone.
Hypogonadism
Men who continuously fail to produce an adequate amount of testosterone suffer from a condition called hypogonadism. This condition can occur during fetal development or before or after puberty, and it results in different consequences on the patient's development, health and appearance. According to the Mayo Clinic, a man who develops hypogonadism as an adult might suffer from infertility, erectile dysfunction and osteoporosis. He might lose muscle mass, develop breasts and lose facial and body hair.
Excess Testosterone
Most men do not suffer from consequences of overproduction of natural testosterone. However, men who have too much testosterone due to abuse of anabolic steroids can develop heart, liver and prostate disease, among other effects.
Aging
As men age, their circulating levels of testosterone decline slowly and steadily. According to the Mayo Clinic, about 30 percent of men over the age of 75 have lower than normal levels of testosterone, but controversy surrounds the idea of boosting the natural levels in these older men. The American Association of Clinical Endocrinologists reports that levels of SHBG in the blood increase about 1 percent each year, so that biologically available testosterone also declines with age.
References
- American Association of Clinical Endocrinologists: Hypogonadism
- Harvard Health: What's a normal testosterone level?
- "Endocrinology: An Integrated Approach"; Stephen Nussey and Saffron Whitehead; 2001
- MayoClinic.com: Hypogonadism
- MSN Health: The perils of too much testosterone
