In the past, there has been a tendency to confuse aging with diseases that are frequently associated with old age. It is, however, important to clearly distinguish the biochemical and physiological processes occurring with the onset of years from pathological conditions, for example cancer, arteriosclerosis (a generic term for several diseases in which the arterial wall becomes thickened and loses elasticity due to, for example, fatty deposits) and neurological disorders such as Alzheimer's disease. It was Fritz Verzar (1886-1979), Swiss gerontologist, who said that "Old age is not an illness; it is a continuation of life with decreasing capacities for adaptation." This view, that aging is a progressive failure of the body's homeostatic adaptive responses, gained wide acceptance only recently.

The obvious characteristics of old age are well known: greying and loss of hair, loss of teeth, wrinkling of the skin, decreased muscle mass and increased...