The endocrine system consists of a group of glands and organs that regulate and control various body functions by producing and secreting hormones. Hormones are chemical substances that affect the activity of another part of the body. In essence, hormones serve as messengers, controlling and coordinating activities throughout the body. (See also Endocrine Glands.)
Levels of most hormones decrease with aging, but some hormones remain at levels typical of those in younger adults, and some even increase. Even when hormone levels do not decline, endocrine function generally declines with age because hormone receptors become less sensitive.
Some hormones that decrease include
In women, the decline in estrogen levels leads to menopause. In men, testosterone levels usually decrease gradually. Decreased levels of growth hormone may lead to decreased muscle mass and strength. Decreased melatonin levels may play an important role in the loss of normal sleep-wake cycles (circadian rhythms) with aging.
Hormones that usually remain unchanged or only slightly decrease include
Hormones that may increase include
Although it seems that hormone replacement therapy might be beneficial in older people with decreased function, such therapy generally does not appear to reverse aging or prolong life and, in some cases (such as estrogen replacement in some older women), is potentially harmful. However, ongoing research is examining the beneficial effects of providing some hormones to older people. Estrogen replacement in older women is discussed in Menopause. Testosterone replacement in older men is discussed in Effects of Aging on the Male Reproductive System.