Considering growth hormone to regain your youth and vitality? If you're willing to shell out thousands of dollars a year, some doctors promise to reverse the signs of aging. But before you sign up, get the facts. Growth hormone is approved only for very specific medical conditions, and it hasn't been proved safe or effective in healthy older adults.

Your body makes growth hormone to help fuel growth in your childhood and to help maintain your tissues and organs throughout your life. Growth hormone is produced in your pituitary gland — a pea-sized structure at the base of your brain. As you age, your body slowly reduces the amount of growth hormone it produces. The level of growth hormone in your body begins to drop in your 40s.

Growth hormone injections are made of synthetic growth hormone that has been genetically engineered. Prior to 1985 — when the first synthetic was available — growth hormone was only available from cadavers.

Growth hormone is available only by prescription. It's currently approved to treat adults with true growth hormone deficiency — not the expected decline in growth hormone due to aging. Growth hormone deficiency can be caused by pituitary tumors and radiation or surgery to the pituitary gland, among other causes.

Growth hormone is also approved for:

• Children with short stature
• Children with kidney disease
• Children with Prader-Willi syndrome
• Children with Turner's syndrome
• Muscle wasting associated with AIDS and HIV

Studies of adults with growth hormone deficiencies show that injections of growth hormone can:

• Increase bone density
• Increase muscle mass
• Decrease body fat
• Bolster the heart's ability to contract
• Improve mood and motivation
• Increase exercise capacity

Because of those results, some people believe that synthetic growth hormone can help healthy older adults who have naturally low levels of growth hormone regain some of their youth and vitality.

Studies of healthy older adults taking growth hormone are limited. Many involve a small number of people followed for a short period of time. The studies that have been conducted have found that growth hormone injections can increase muscle mass and reduce the amount of body fat in healthy older adults.

That increase in muscle doesn't translate into increased strength. Though the study participants gained muscle, they weren't any stronger. One study compared older men who took growth hormone with older men who went through strength training programs. The bottom line: strength training can increase both your muscle mass and your strength, making it cheaper and more effective than taking growth hormone.

It isn't clear whether growth hormone can provide other benefits, such as increased bone density and improved mood, to healthy adults. Most of the research into human growth hormone has focused on the people who truly need it — those with true growth hormone deficiencies.

Taking growth hormone can cause a number of side effects, including:

• Swelling in your arms and legs
• Arthritis-like symptoms
• Carpal tunnel symptoms
• Headaches
• Bloating
• Muscle pain
• Diabetes
• Abnormal growth of bones and internal organs
• Hardening of the arteries
• High blood pressure

Some evidence shows that side effects of growth hormone may be more likely in people over the age of 60 than in younger adults. Also, because the studies of healthy adults taking growth hormone have been short term, it isn't clear whether these side effects could eventually dissipate or become worse. For instance, though growth hormone produced arthritis-like symptoms, it isn't clear if this would progress into arthritis. More study is needed.

Some Web sites claim to sell a pill form of growth hormone that produces results similar to the injected form of the drug. Sometimes these are called human growth hormone releasers. No proof substantiates these claims. In fact, if you were to swallow growth hormone, it would likely be digested by your stomach acids and not absorbed into your body.

Web sites also sell homeopathic remedies claiming to contain growth hormone. No proof shows that these work, either.

Your doctor can explain more about how growth hormone works in your body and whether it's something your body needs more of. If you have specific concerns about aging, such as gaining weight, your doctor can suggest ways to improve your health safely. Taking simple steps, such as eating a balanced diet full of fruits and vegetables and exercising daily, can help keep your body in shape and help you feel better about yourself as you age.