Aging is an accumulation of molecular damage and its consequences. The greater the level of damage, the greater the dysfunction in organs and the immune system, then the closer the individual comes to the arbitrary dividing line at which that dysfunction becomes a formal, named age-related disease. Further, the more damage, the higher the mortality rate. Given this view of aging, it should be no great surprise to find that the longest lived people have a history of comparatively little age-related disease: the only ways to become extremely old are to either (a) have accumulated damage at a slower rate that everyone else, most likely through lifestyle choices, or (b) bear genetic variants that increase resistance to some forms of damage and consequence. In either case, cell and tissue damage, aging, longevity, and age-related disease are all linked together, facets of the same whole.

In a large cohort of predominantly male community-dwelling elderly veterans, centenarians had a lower incidence of chronic illness than those in their 80s and 90s. The centenarian population is one of the fastest growing in the country, according to the United States Social Security Administration. They are predicted to exceed one million by the close of this century, little is known about why this generation has achieved such longevity. In a recent study, researchers looked primarily at octogenarians, nonagenarians, and centenarians within the Veterans Affairs medical system. The sample that they studied comprised mostly of white males that had fought in World War II. "Additionally, this generation lived through the Great Depression. It is a wonder, considering the hardships they had faced, that they have achieved such longevity."

A key factor that the research team observed in these individuals is that, due to their military background, many had a developed sense of discipline and therefore were keen to make healthy decisions; many did not smoke or drink. The team also offered the hypothesis of compression of morbidity as a potential explanation for the extended health span in an individual's life span. The hypothesis states that the lifetime burden of illness could be reduced if the onset of chronic illness is postponed until very late in life, or in other words "the older you get, the healthier you have been."

Ninety-seven percent of centenarians were male, 88.0% were white, 31.8% were widowed, 87.5% served in World War II, and 63.9% did not have a service-related disability. The incidence rates of chronic illnesses were higher in octogenarians than centenarians (atrial fibrillation, 15.0% vs 0.6%; heart failure, 19.3% vs 0.4%; chronic obstructive pulmonary disease, 17.9% vs 0.6%; hypertension, 29.6% vs 3.0%; end-stage renal disease, 7.2% vs 0.1%; malignancy, 14.1% vs 0.6%; diabetes mellitus, 11.1% vs 0.4%; stroke, 4.6% vs 0.4%) and in nonagenarians than centenarians (atrial fibrillation, 13.2% vs 3.5%; heart failure, 15.8% vs 3.3%; chronic obstructive pulmonary disease, 11.8% vs 3.5%; hypertension, 27.2% vs 12.8%; end-stage renal disease, 11.9% vs 4.5%; malignancy, 8.6% vs 2.3%; diabetes mellitus, 7.5% vs 2.2%; and stroke, 3.5% vs 1.3%).