Aging and Life Span

Many of the diseases common in older adults, such as cardiovascular disease, cancer, dementia, arthritis, blindness, and deafness, are consequences of the acceleration or distortion of these "natural" changes associated with aging. These complex diseases associated with aging are caused by the interaction of genetic and environmental factors. For example, Alzheimer's disease is an illness caused by changes in the brain that impair thinking and memory much more severely than the natural decline that all humans experience during aging. It is the most common form of dementia in adults over age sixty. Certain very rare alleles are associated with the development of Alzheimer's disease, and other much more common alleles (of different genes) increase the risk of a variety of other diseases. Environmental factors such as exposure to toxins have also been implicated. A more rare example is progeria, a disease in which the tissues of the body age about seven times more rapidly than normal. In this case, a person who is chronologically only a teenager looks much older.