When it comes to hormones, testosterone is among the most widely misunderstood. This sex hormone is produced in a man's testes and adrenal glands and, in smaller amounts, in a woman’s ovaries and adrenal glands. It affects sex drive in both men and women. In men, it also plays a role in strength, mood, the development of sex organs and secondary male sexual characteristics like hair growth.

Even though a significant number of men over age 50 suffer from a deficiency of the hormone, few receive appropriate treatment. Women also can be affected by symptoms when their bodies do not produce enough testosterone. What you need to know…

Beyond Sexual Dysfunction

Until fairly recently, doctors believed that the only casualty of the waning testosterone levels that occur when a man ages was his sex drive (libido).

Now: It's known that low testosterone can cause a variety of other symptoms. For example…

  • Fatigue. Men with low testosterone often tire more easily and take more naps.
  • Low mood. Irritability and depression can occur.

Low testosterone also can lead to hidden problems, such as…

  • Anemia. A shortage of red blood cells may be due to such causes as a nutritional deficiency, gastrointestinal bleeding—or low testosterone.
  • Bone loss. Osteoporosis isn't just a woman's disease—more than 6% of men have developed it by age 65—and testosterone deficiency greatly increases the risk. .Loss of muscle mass. Belly fat also can develop.

Are You Deficient?

Unfortunately, few men who experience these symptoms receive a blood test for testosterone deficiency. The test that measures total testosterone levels is the best known. But free testosterone levels should be measured (also with a blood test) to determine the amount of the hormone that can be used most readily by the body.

Important: There is debate regarding the exact definition of “normal" blood levels of both total and free testosterone. Speak to your physician for an interpretation of your test results.

Low numbers on either test—in addition to the symptoms described earlier—usually warrant a trial of testosterone therapy. It may take up to three months to see benefits.

What Are The Risks?

The long-term effects of testosterone therapy are unknown, but research is beginning to ad-dress many of the concerns some men have had regarding the potential risks of testosterone replacement.

Among the most common…

  • Heart disease. Men are more prone to heart disease than women are, and testosterone was once considered a likely explanation. But there is virtually no evidence that supports this theory.

In fact, one study found that men with higher testosterone levels are less likely to develop atherosclerosis (fatty buildup in the arteries) than those with low testosterone. Low testosterone is associated with diabetes and obesity—major risk factors for heart attack.

Caution: Testosterone boosts red blood cell production. This is good for anemia, but too many red blood cells can raise heart attack risk. Men with high hematocrit (a measure of red blood cell concentration) should use testosterone cautiously, if at all. Men with advanced kidney or liver disease should avoid testosterone therapy—it could cause fluid retention, which already is a problem for such men.

  • Prostate cancer. There has been concern that testosterone may fuel the growth of prostate cancer and that testosterone therapy could stimulate small, unsuspected tumors.

While it is true that lowering testosterone levels to zero does make prostate tumors shrink. there is now strong evidence that raising testosterone levels in men who have testosterone deficiency does not increase prostate cancer risk.

A new and controversial issue is whether men who have been treated for prostate cancer can receive testosterone therapy. Early data suggest that this may be safe in certain men. Discuss it with your doctor.

Using Testosterone

Testosterone replacement can be administered in a variety of ways…

  • Injections are usually given by a doctor or nurse every two to three weeks. Some men learn to inject themselves.

Typical cost: About $10 per injection.

  • Gel can be rubbed into the skin (typically on the chest, shoulders and upper arms) daily. For 80% to 85% of men, the gel works as well as injections.

Typical cost: $200 to $500 per month.

  • Pellets containing testosterone are kin-planted under the skin during a five-minute office procedure. Treatment generally lasts for three to six months.

Typical cost: $500 to $600 per treatment.

  • Skin patches usually are not as effective as the other forms described above.

If you're interested in testosterone therapy, consult your primary care physician, who may refer you to a urologist or an endocrinologist (a doctor who specializes in the treatment of hormone disorders).

Important: Any man who receives testosterone therapy should have his prostate-spec:0c antigen (PSA) levels measured at least annually. Elevated PSA levels can indicate prostate cancer or benign enlargement of the prostate. PSA levels often rise within three months of starting testosterone therapy but should stabilize afterward.

How Women Can Be Affected

Like men, women experience a drop in testosterone levels as they age. Low testosterone may be implicated if a woman loses her sex drive—either before or after menopause. None of the testosterone preparations described above are FDA-approved for use in women.

But in a recent study that appeared in The New England Journal Ty-Medicine and involved more than 800 postmenopausal women, year-long use of a testosterone skin patch raised de-sire and the frequency of satisfying sexual episodes from 0.7 to 2.1 per month, on average.

Women may suffer side effects from testosterone therapy—unwanted hair growth, in particular. The long-term effects of testosterone therapy in women are unknown.

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