Though important for both men's and women's general health, a man's body can produce about 20 times more testosterone than a woman's body.

During the aging process for men, testosterone levels can drop. This part of the aging process — usually occurring between the ages of 40 and 55 — is sometimes referred to as andropause, similar to menopause in women. A loss of testosterone can contribute to excessive weight gain, loss of muscle mass, osteoporosis and general fatigue.

There are some symptoms of testosterone deficiency to watch for. Natural changes to the body occur with age, including decreased muscle mass and an increase in body fat. But without adequate testosterone, a man can lose sex drive, have erectile dysfunction or feel depressed.

According to WebMD, the only accurate way to detect testosterone deficiency is to the amount of testosterone in the blood measured by a doctor. Because testosterone levels fluctuate throughout the day, several measurements need to be taken to detect a deficiency. Some doctors prefer to test levels early in the morning, because that's when testosterone levels are at their highest.

While middle-aged men may be eager to try the hormone, which has been touted as a cure-all for everything from lack of strength to lack of libido, there are questions about the safety of undergoing therapy.

One problem doctors have in answering this question is that they have not been following patients undergoing the process long enough to say it is completely safe. The FDA says testosterone replacement should only be used to treat a condition called male hypogonadism, which means that the testes aren't producing sufficient amounts of testosterone.

That's partly because testosterone is known to increases levels of prostate specific antigen, or PSA. Increased PSA levels are a marker for prostate cancer, although some PSA increases are caused by a noncancerous enlargement of the prostate, which is called benign prostatic hyperplasia, according to WebMD.

The recipe for men for slowing testosterone loss with age is comprised of the ingredients for general good health: don't smoke and keep excess weight off.

To keep their biological clock from speeding up, doctors say men should try to keep their midsection trim. Excess belly fat seems to break down testosterone more quickly, speeding many of the symptoms that characterize the aging process.

Learn more about testing at WebMD.

Read more from the Male Reproductive Center at Columbia University in New York.

Is testosterone replacement therapy safe? WebMD weighs in.

Learn more about andropause.

• Click here for information from the Society for Male Production and Urology.

• You can read more about biological clocks from the National Institute of Mental Health.