Free-radical theory
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The free-radical theory of aging is that organisms age because cells accumulate free radical damage with the passage of time. For most biological structures free radical damage is closely associated with oxidation damage. Oxidation and reduction are redox chemical reactions. Most people can equate to oxidation damage as they are familiar with the process of rust formation of iron exposed to oxygen. Oxidation does not necessarily involve oxygen, after which it was named, but is most easily described as the loss of electrons from the atoms and molecules forming such biological structures. The inverse reaction, reduction, occurs when a molecule gains electrons. As the name suggests, antioxidants like vitamin C prevent oxidation and are often electron donators.
In biochemistry, the free radicals of interest are often referred to as "reactive oxygen species" (ROS) because the most biologically significant free radicals are oxygen-centred; however it should be noted that not all free radicals are ROS and not all ROS are free radicals.
Denham Harman first proposed this theory that aging was a consequence of free radical damage in the 1950s (PMID 13332224) and extended the idea over subsequent decades. Of all the theories of aging, Harman's has the most consistent experimental support.
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Theory of disease
One of the underlying concepts that guided Harman to his theory of aging was the involvement of free radicals in disease. Free radical damage within cells, and subsequent damage has been linked to a range of disorders including cancer, arthritis, atherosclerosis, Alzheimer's disease, and diabetes. This involvment is not at all surprising as free radical damage is an important aspect of phagocytosis, inflammation, and apoptosis. Cell suicide, or apoptosis, is the body's way of controlling cell death and involves free radicals and redox signalling. Redox factors play an even greater part in other forms of cell death such as necrosis or autoschizis.
More recently, the relationship between disease and free radicals has led to the formulation of a greater generalisation. The free radical theory of disease states that disease is associated with abnormal levels of oxidation and the generation of free radical damage. In its strong form, the hypothesis states that all disease depends upon free radical damage. The weaker statement of the hypothesis is that disease generally involves free radical processes.
Evidence
- Results have demonstrated that the overexpression of catalase, an enzyme involved in the decomposition of hydrogen peroxide (a free radical), increased both the average lifespan and maximum lifespan of mice by 20% (PMID 15879174).
- Making a well-studied roundworm, Caenorhabditis elegans, more susceptible to free radicals has led to premature aging (PMID 11237107).
- A press release by the American Physiological Society shows that mitochondria (which provide the body with most of its energy) become more effective when they contain fewer products that have been generated by free radicals (PMID 16020519).
Antioxidant therapy
The theory implies that antioxidants (e.g. Vitamin A, vitamin C, and vitamin E) — which prevent free radicals from oxidizing sensitive biological molecules, or reduce the formation of free radicals — will slow the aging process and prevent disease.
The antioxidant chemicals found in many food-stuffs (such as the well known vitamins A, C and E) are frequently cited as the basis of claims for the benefits of a high intake of vegetables and fruits in the diet. In particular, antioxidant therapy forms the basis of many basic pharmacological interventions and particularly orthomolecular medicine. A particularly interesting development, the dynamic flow model, is a hypothesis originating with the suggestion by Dr. Robert Cathcart that massive intakes of ascorbate can quench disease processes.
Calorie restriction
See main article: Calorie restriction
Calorie restriction, or severely cutting the intake of energy, has been found to reduce ROS and to increase the life-span of rodents. Studies have shown that both calorie restriction and reduced meal frequency/intermittent fasting can suppress the development of various diseases and can increase life span in rodents by 30-40% by mechanisms involving stress resistance and reduced oxidative damage. Severe calorie restriction over 50% resulted in increased mortality (PMID 16011467).
The greatest proponent of calorie restriction as a way to longer life was the late Dr. Roy Walford (1924-2004), formerly Professor of Pathology at the University of California, Los Angeles School of Medicine.
See also
External links
Calorie restriction
Biology of Aging
- Damage-Based Theories of Aging Includes a discussion of the free radical theory of aging.
- The Free Radical Theory of Aging