This loss of capabilities is progressive, irreversible, and universal for all humans. This process called "aging" shows itself in many ways, sometimes a decline in height, shrinkage of muscle, thinning and graying of hair, and wrinkling of skin. Internally, there is a loss of cells in the brain, kidneys, and other vital organs. Important tissues like the muscles to the brain shrink and become less competent with age. Many of these changes cause functional declines. Not only do nerve cells from the brain to the spinal cord diminish, but also those that remain conduct impulses at a slower rate so that the reaction time of an older person is slowed. Memory also shows a decline.

Another widespread decline is in the loss of cells involved in the hearing process. The loss is mostly for higher pitched sounds. Declines are also noted for coping with infection. Infections due to pneumonia are common in the aged. In fact, it is one of the most common causes of death among the elderly.

Complicating the aging process are diseases that are so common that they are often mistaken for aging. For example, the buildup of fatty deposits in arteries (atherosclerosis, or hardening of the arteries) tends to be progressive with aging; at least in American society ... and the narrowing of arteries results in serious illnesses like stroke (in arteries to the brain) or heart attack (in arteries to the heart).

It is interesting to note that many people are able to escape atherosclerosis, and some undernourished populations have virtually no incidence of the disease.

It is now recognized that atherosclerosis is the result of "life-style" factors ... like high blood pressure, high saturated-fat diets, and smoking.

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