Quiz: The Truth About Testosterone

It's normal to have a lower sex drive and fewer spontaneous erections as you age. But little or no libido can be a sign that you have low testosterone. Research suggests that almost 40% of men ages 45 and older seen in a doctor’s office may have low testosterone.

Because the symptoms of low testosterone can be vague and because men don't always mention their symptoms to their doctors, the actual number of men with low testosterone levels may be higher.

A decline in testosterone levels is normal with aging. Low testosterone levels are levels that are considerably lower than what's normal for your age. That's not a normal part of aging. It can affect your quality of life and health. And it can be remedied.

Low testosterone can alter some typical masculine features in men. Painful breasts or breast enlargement may suggest low testosterone in men. Other signs are losing body hair and having to shave less frequently. Also, your testicles may be smaller when testosterone is low, and it may be difficult to get or keep an erection. Hot flashes are most often seen in men who have very low testosterone.

Testosterone doesn't just relate to sex. It helps build bone, and low testosterone can lead to frail bones and osteoporosis. Testosterone may also help keep muscles strong. It helps produce red blood cells, boosts mood, and aids thinking. Low testosterone may cause anemia, depression, and trouble concentrating.

Many men with low testosterone don't have symptoms. Only a blood test can tell what your testosterone levels are. The Endocrine Society considers 300 to 1,200 nanograms per deciliter (ng/dL) normal and less than 300 low. Doctors usually use a blood test and a number of symptoms to make a diagnosis and determine whether treatment is needed.

From puberty, when a boy starts to get a beard and pubic hair, testosterone affects hair growth in men. But it doesn't affect growth on all parts of the body the same way. Low testosterone can cause you to lose body or facial hair, but it doesn't cause male pattern baldness. Genetics have more to do with that.

Low testosterone can be a cause of erectile dysfunction (ED) -- the inability to get or keep an erection -- and testosterone therapy may help treat it. But in some cases, testosterone treatment does not improve ED symptoms because there are other causes. For example, diseases of the nerves and blood vessels can also affect the penis and cause ED. If you have ED, talk to your doctor.

Beginning in a man's 40s, his testosterone levels start to fall about 1% a year.  This is a normal decline that occurs as men age. Men whose testosterone levels are below normal may or may not have symptoms of low testosterone. When they do, your doctor may recommend treatment with testosterone therapy.

Obesity does increase your risk of having a lower testosterone level. If your blood tests show a low testosterone level and you have symptoms, your doctor will likely do more testing before prescribing any treatments.

Testosterone replacement therapy has been used since the 1940s. Injections, usually given every few weeks, are one of the oldest ways to increase testosterone. Gels are used widely in the U.S. They are applied daily to the shoulder, abdomen, or upper arm. The general goal of treatment is to raise the blood testosterone level only into the mid-normal range -- about 400-700 ng/dL. Other methods include patches, oral adhesive tablets and TESTOPEL (testosterone pellets), which is a pellet that is injected subcutaneously and can last 3-6 months.

Anabolic steroids, often used by athletes and weightlifters, mimic the body's natural testosterone in bulking up muscles. But using them can actually lower testosterone. Excess anabolic steroids may also increase aggression in men, cause severe acne or trembling, shrink testicles and sperm count, and cause baldness.

Finasertide, used to treat male pattern baldness, can increase testosterone blood levels. Other drugs can lower testosterone. These include corticosteroids such as prednisone, used for inflammatory conditions, and long-acting narcotics, like oxycodone and morphine. Drugs used to treat advanced prostate cancer can also lower testosterone levels.

Testosterone replacement therapy may make some medical conditions worse, such as sleep apnea, which causes pauses in breathing during sleep. It is not recommended for men with severe sleep apnea, severe benign prostatic hypertrophy, or lower urinary tract infections. Other illnesses that don't mix with testosterone therapy include prostate cancer, male breast cancer, and congestive heart failure that is uncontrolled or poorly controlled.

Alcohol is directly toxic to the testicles, where testosterone is produced, and it seems to affect the release of other hormones related to men's sexual function and fertility. Shrunken testicles are a common sign of low testosterone in alcoholic men with liver disease, as well as lower libido and sexual potency. Enlarged breasts are common in heavy drinkers because alcohol may help convert testosterone into the female hormone estrogen.

Testosterone therapy does more than give your libido a lift. Studies show that it may improve thinking and energy and that it does improve mood. It may also increase muscle strength and mass, as well as help treat osteoporosis. It may even make you more alert, but it won't help you play the piano.

Up to 9 out of 10 men who have symptoms of low testosterone may not get treatment. They may attribute their symptoms to other conditions or think they're a normal part of aging. If you have symptoms and believe they are having an impact on your quality of life and well-being, talk to your doctor.