Aging: Can Hormones Prevent Aging? (cont.)

In fact, many of the changes that take place in older men often are incorrectly blamed on decreasing testosterone levels. Some men who have erectile dysfunctiondifficulty (impotence), for instance, may be tempted to blame this problem on lowered testosterone. However, in many cases, erectile difficulties are due to circulatory problems, not low testosterone.

Still, some men may be helped by testosterone supplementation. These FDA approved products are prescribed for men whose bodies make very little or no testosterone-for example, men-whose pituitary glands have been damaged or destroyed by trauma, infections or tumors, or whose testes have been damaged. For these few men who have extreme deficiencies, testosterone therapy in the form of patches, injections, or topical gels may offer substantial benefit. Testosterone products may help a man with exceptionally low testosterone levels maintain strong muscles and bones, and increase sex drive. However, what effects testosterone replacement may have in healthy older men without these extreme deficiencies requires more research.

The NIA is investigating the role of testosterone therapy in delaying or preventing frailty. Results from preliminary studies involving small groups of men have been inconclusive, and it remains unclear to what degree supplementation of this hormone can sharpen memory or help men maintain stout muscles, sturdy bones, and robust sexual activity.

Many other questions remain about the use of this hormone in late life. It is unclear, for example, whether men who are at the lower end of the normal range of testosterone production would benefit from supplementation. Some investigators are also concerned about the long-term harmful effects that supplemental testosterone might have on the aging body. It is not yet known, for instance, if testosterone therapy increases the risk of prostate cancer, the second leading cause of cancer death among men. In addition to potentially promoting new prostate cancers, testosterone also may promote the growth of those that have already developed. Studies also suggest that supplementation might trigger excessive red blood cell production in some men. This side effect can thicken blood and increase a man's risk of stroke.

The bottom line: Although some older men who have tried testosterone therapy report feeling "more energetic" or "younger," testosterone supplementation remains a scientifically unproven method for preventing or relieving any physical and psychological changes that men with normal testosterone levels may experience, as they get older. Until more scientifically rigorous studies are conducted, the question of whether the benefits of testosterone replacement outweigh any of its potential negative effects will remain unanswered. The NIA is planning to expand its research to gather more evidence on the risks and benefits of testosterone supplementation in aging men with low testosterone levels.

Estrogen and Progesterone

Estrogen and progesterone are hormones produced in a woman's ovaries before menopause. They play an important part in the menstrual cycle and pregnancy, but estrogen also helps maintain bone strength and might prevent heart disease and protect memory before menopause.

For more than 60 years estrogen has been used by millions of women to control the hot flashes and vaginal dryness that frequently occur with menopause. It is also used to prevent or treat osteoporosis, the loss of bone strength that often occurs after menopause. However, over time experts realized that estrogen could cause a thickening of the lining of the uterus (endometrium) and an increased risk of endometrial cancer. Doctors then began giving progestin, a synthetic form of progesterone, to protect the lining of the uterus. Using estrogen alone (in a woman whose uterus has been removed) or with a progestin (in women with a uterus) to treat the symptoms of menopause is called menopausal hormone therapy (MHT), formerly known as hormone replacement therapy.

Unlike other hormones described in this fact sheet, many large, reliable long-term studies of estrogen and its effects on the body have been conducted. These studies suggested that using estrogen after menopause could provide many important benefits.

But estrogen also is a good example of why it is important to wait until researchers have discovered both the benefits and risks of a hormone before it becomes widely used. While some women are helped by estrogen during and after menopause, others are placed at higher risk for certain diseases if they take it.

Early studies suggested menopausal hormone therapy could lower the risk for heart disease (the number-one killer of women in the United States) in postmenopausal women. But results from the Women's Health Initiative (WHI), an important study of menopausal hormone therapy funded by the National Institutes of Health, now suggests that using estrogen with or without a progestin after menopause does not protect postmenopausal women (ages 50 and older) from heart disease and may even increase their risk. In 2002, WHI scientists reported that using estrogen plus progestin actually elevates some women's chance of developing heart disease, stroke, blood clots, and breast cancer. But they also found health benefits-not as many hip fractures and fewer cases of colorectal cancer. In 2004, the same scientists reported that using estrogen alone increased a woman's risk of stroke and blood clots, but protected women from hip fractures.