Energy metabolism and oxidative stress: impact on the metabolic syndrome and the aging process.

Aging can be defined as a progressive decline in the ability of the organism to resist stress, damage, and disease. Although there are currently over 300 theories to explain the aging phenomenon, it is still not well understood why organisms age and why the aging process can vary so much in speed and quality from individual to individual. The oxidative stress hypothesis is one of the prevailing theories of aging. This theory states that free radicals produced during cellular respiration damage lipids, proteins, and DNA thereby accelerating the aging process and increasing disease risk. Under normal conditions, the electron transport chain is the primary producer of the superoxide anion, which is precursor to other highly reactive species such as hydrogen peroxide and the hydroxyl radical. Oxidative stress accumulates when prooxidants overwhelm the antioxidant defense mechanisms. This is dependent on a number of factors including free radical production, susceptibility of tissue to stress, and strength of the defense and repair system. Oxidative stress has been implicated in a number of chronic disease states usually grouped under the umbrella of the metabolic syndrome and is thought to contribute to the aging process. It has been hypothesized that the production of free radicals is dependent on resting metabolic rate and this may have an impact on the aging process. However, other factors, such as mitochondrial function, may be important in the production of free radicals and the subsequent effect on aging and disease states.