Anti-Aging

Life extension, also known as anti-aging medicine, experimental gerontology, and biomedical gerontology, refers to attempts to slow down or reverse the processes of aging to extend both the maximum and average lifespan. Some researchers in this area, and "life extensionists" or "longevists" (who wish to achieve longer lives for themselves), believe that future breakthroughs in tissue rejuvenation with stem cells, molecular repair, and organ replacement (such as with artificial organs or xenotransplantations) will eventually enable humans to have indefinite lifespans through complete rejuvenation to a youthful condition.

The sale of putative anti-aging products such as nutrition, physical fitness, skin care, hormone replacements, vitamins, supplements and herbs has become a lucrative industry, with the US market generating about $50 billion of revenue each year. Medical experts state that the use of such products has not been shown to affect the aging process, and many claims of anti-aging medicine advocates have been roundly criticized by medical experts, including the American Medical Association

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. Extension of average lifespan 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.

Much of life extension has been concerned with the use of nutrition, in the form of diets or supplements, to extend lifespan. 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.[citation needed] 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 (a practice generally called Calorie restriction or simply CR) 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.[citation needed] 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.[citation needed] 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.