Aging is an accumulation of damage to macromolecules, cells, tissues and organs. The maximum life span for humans is in excess of 120 years, whereas the maximum lifespan of a mouse, commonly used as a model in research on aging, is about four years. Genetic differences between humans and mice that may account for these different aging rates include efficiency of DNA repair, types and quantities of antioxidant enzymes, and different rates of free radical production.

Average lifespan in a population is lowered by infant and child mortality, which are frequently linked to infectious diseases or nutrition problems. Later in life, vulnerability to accidents and age-related afflictions such as cancer or cardiovascular disease play larger roles. Life extension can be achieved by good diet, exercise and avoidance of hazards such as smoking. Maximum lifespan is determined by the rate of aging for a species inherent in its genes and probably by certain environmental factors. One widely recognized method of extending maximum lifespan in organisms such as nematodes is calorie restriction. Another technique used evolutionary pressure such as breeding from only older members. Theoretically, extension of maximum lifespan could be achieved by reducing the rate of aging damage, by periodic replacement of damaged tissues, or by molecular repair or rejuvenation of deteriorated cells and tissues.

Many scientific anti-aging products been concerned with the use of nutrition, in the form of diets or supplements, to extend lifespan. Withing these supplements anti-oxidants have proven to be the most significant component for anti-aging. Recently it has been suggested that Resveratrol may be a great resource of anti-oxidants.

Antioxidants can cancel out the cell-damaging effects of free radicals.[1] Furthermore, people who eat fruits and vegetables, which happen to be good sources of antioxidants, have a lower risk of heart disease and some neurological diseases, and there is evidence that some types of vegetables, and fruits in general, protect against a number of cancers. These observations suggested the idea that antioxidants might help prevent these conditions. However, this hypothesis has now been tested in many clinical trials and does not seem to be true, since antioxidant supplements have no clear effect on the risk of chronic diseases such as cancer and heart disease. This suggests that other substances in fruit and vegetables, or a complex mix of substances, may contribute to the better cardiovascular health of those who consume more fruit and vegetables. However, there is some evidence that antioxidants might help prevent other diseases such as macular degeneration, suppressed immunity due to poor nutrition, and neurodegeneration.

It is thought that oxidation of low density lipoprotein in the blood contributes to heart disease, and initial observational studies found that people taking Vitamin E supplements had a lower risk of developing heart disease. Consequently, at least seven large clinical trials were conducted to test the effects of antioxidant supplement with Vitamin E, in doses ranging from 50 to 600 mg per day. However, none of these trials found a statistically significant effect of Vitamin E on overall number of deaths or on deaths due to heart disease. Further studies have also been negative. It is not clear if the doses used in these trials or in most dietary supplements are capable of producing any significant decrease in oxidative stress. Overall, despite the clear role of oxidative stress in cardiovascular disease, controlled studies using antioxidant vitamins have observed no reduction in either the risk of developing heart disease, or the rate of progression of existing disease.

While several trials have investigated supplements with high doses of antioxidants, the “Supplémentation en Vitamines et Mineraux Antioxydants” (SU.VI.MAX) study tested the effect of supplementation with doses comparable to those in a healthy diet. Over 12,500 French men and women took either low-dose antioxidants or placebo pills for an average of 7.5 years. The investigators found there was no statistically significant effect of the antioxidants on overall survival, cancer, or heart disease. However, in a post-hoc analysis they found a 31% reduction in the risk of cancer in men, but not women.

Many nutraceutical and health food companies sell formulations of antioxidants as dietary supplements and these are widely used in industrialized countries. These supplements may include specific antioxidant chemicals, like resveratrol (from grape seeds or knotweed roots), combinations of antioxidants, like the “ACES” products that contain beta carotene (provitamin A), vitamin C, vitamin E and Selenium, or herbs that contain antioxidants – such as green tea and jiaogulan. Although some levels of antioxidant vitamins and minerals in the diet are required for good health, there is considerable doubt as to whether these antioxidant supplements are beneficial or harmful, and if they are actually beneficial, which antioxidant(s) are needed and in what amounts. Indeed, some authors argue that the hypothesis that antioxidants could prevent chronic diseases has now been disproven and that the idea was misguided from the beginning.

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For overall life expectancy, it has even been suggested that moderate levels of oxidative stress may increase lifespan in the worm Caenorhabditis elegans, by inducing a protective response to increased levels of reactive oxygen species. However, the suggestion that increased life expectancy comes from increased oxidative stress conflicts with results seen in the yeast Saccharomyces cerevisiae, and the situation in mammals is even less clear. Nevertheless, antioxidant supplements do not appear to increase life expectancy in humans.

The many diets promoted by anti-aging advocates are often contradictory. One of the few areas of consensus among nutritionists is the importance of keeping stable blood sugar levels, achieved in part by managing the glycemic indices of food choices. Two diets with different approaches and some support from scientific research are the Paleolithic diet and Caloric restriction.

The restriction of energy intake, or calories, in an otherwise healthy diet has been shown to extend the maximum life span of laboratory organisms from several species, including rats, yeast, fruit flies, and nematodes. In rodents, a roughly 50% maximum lifespan extension is seen with a roughly 50% restriction of calories from what would be consumed by freely-feeding animals. The results of calorie restriction experiments on laboratory rats may not be generalizable because years of inbreeding have made these animals different from those found in the wild, and because these results are applicable specifically to short-lived species that have evolved to respond to feast and famine with alterations in longevity. Proving that calorie restriction could extend human life is difficult because experiments with long-lived species necessarily take a long time to perform. Scientists propose that the results of calorie restriction experiments on animals also depend on the habitat, genetics, other aspects of nutrition and frequencies of feeding.

The idea that antioxidant supplements, such as Vitamin C, Vitamin E, lipoic acid and N-acetylcysteine, might extend human life stems from the free radical theory of aging. Other substances proposed to extend lifespan include oxytocin, insulin, human chorionic gonadotropin (hCG) and erythropoietin (EPO). Resveratrol is a sirtuin stimulant that appears to extend lifespan in simple model organisms such as nematodes and short-lived fish.

Some supplements, including the minerals selenium or zinc have been reported to extend the lifespan of rats and mice, though none has been proven to do so in humans, and significant toxic effects were observed. Metformin may also extend life span in mice.