A study of markers of oxidative stress in centenarians: "Human longevity is a complex phenotype that is determined by environment, genetics, and chance. Understanding the mechanisms by which aging leads to longevity, particularly healthy longevity would be of enormous benefit to our aging population. Unfortunately, most research on human aging has focused on phenomenological description of age-related diseases, and much less is known about the mechanisms of aging itself. Among the most promising theories about how and why we age is the Free Radical Theory, initially proposed by Denham Harman in 1956. Harman proposed that oxygen radicals produced during aerobic respiration induce oxidative damage in DNA, cells, tissues, and organisms that lead to aging and death. ... Harman hypothesized, based on observations of enzymatic redox chemistry, that oxygen radical generation occurs in vivo and that mechanisms exist to protect against such damage. Mitochondria were later found to be a principal source of these oxygen radicals ... Okinawa has among the world's longest-lived populations but oxidative stress in this population has not been well characterized. ... The low plasma level of [oxidized lipids] in Okinawan centenarians, compared to younger controls, argues for protection against oxidative stress in the centenarian population and is consistent with the predictions of the Free Radical Theory of Aging."