Diet, Other Risk Factors,
People may develop a variety of diseases as they age. These include disorders of the blood vessels (usually atherosclerotic), cancers of many different organs, diseases of the joints, and gradual loss of lung tissue and brain cells. Many of these diseases have well-understood pathological mechanisms, the effects of which become more prominent in later years.
This age-dependency aspect of disease can simply result from an older person's longer exposure to harmful environmental influences. Older subjects indeed have the possibility of longer exposure to a poor diet, cigarette smoking, physical wear and tear on joints, ultraviolet and gamma radiation, and other hazards. If the effects of these factors are cumulative over time, disease will be more common in the elderly. There may also be cohort effects, whereby elderly subjects in earlier periods of their life had less adequate medical care and less knowledge of preventive medicine, and therefore lived less healthfully. Many more older men than younger men, for instance, are past smokers or past consumers of diets heavy in animal fat.
Our health is affected in a complex way by interactions between environmental factors, health habits, and genetic predisposition. In certain strongly familial forms of Alzheimer's disease, or in the hereditary neurological disorder Huntington's chorea, for instance, the characteristic clinical abnormalities due to genetic defects are displayed only by middle age. This introduces the idea that genes affecting aging may also be programmed to turn on at particular times during the life cycle.
A fundamentally different pathologic process is also associated with advanced age but does not target particular bodily organs or severe dysfunction of isolated metabolic systems, such as those that may underlie cancer or atherosclerosis. Rather, this process involves a general decline in the