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. Bioethicists question whether and how the human lifespan should be extended.
Aging
Main article: SenescenceAging 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.
Current anti-aging strategies and issues
Diets and supplements
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. 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. 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.
Cosmetics
Cosmetic interventions such as skin treatments (e.g., skin resurfacing, Botox treatments, Argireline products) and plastic surgery are widely used to mask the effects of aging, although they do not actually affect lifespan.
Hormone treatments
The anti-aging industry offers several hormone therapies. Some of these products have been criticized, for example by the American Medical Association, for possible dangers to the patient and a lack of proven effect.
The evidence for use of growth hormone is mixed and based on animal studies. An early study suggested that supplementation of mice with growth hormone increased average life expectancy. Additional animal experiments have suggested that growth hormone may generally act to shorten maximum lifespan; knockout mice lacking the receptor for growth hormone live especially long. Furthermore, mouse models lacking the insulin-like growth factor also live especially long and have low levels of growth hormone.
The synthetic estrogen Premarin (made from mare’s urine), has been proposed to reduce the impact of menopause. In 1991, the Women’s Health Initiative studied 161,808 postmenopausal women with randomized trials of hormone supplements or placebo. It discontinued the study in 2002 because it concluded that, on the whole, the supplements were doing more harm than good (primarily due to an increased risk of breast cancer). Testosterone supplements in the form of creams or patches have been proposed for men. Regular Human Growth Hormone (HGH) injections cost about $10–12,000 a year. On the internet, many websites promote less expensive secretagogues that claim to prompt the body to produce HGH. There is little independent research on HGH secretagogues.
Scientific controversy regarding anti-aging nutritional supplementation and medicine
Leonard Hayflick, who determined that fibroblasts are limited to around 50 cell divisions, disputes the claim that aging is a disease. Hayflick reasons that aging is an unavoidable consequence of entropy. Hayflick and fellow biogerontologists Jay Olshansky and Bruce Carnes have strongly criticized the anti-aging industry in response to what they see as unscrupulous profiteering from the sale of unproven anti-aging supplements.
Ethics and politics of anti-aging nutritional supplementation and medicine
Politics relevant to the substances of life extension pertain mostly to communications and availability. In the United States, the claims which can be made on food and drug product labels are strictly regulated. Meanwhile, freedom of speech guaranteed by the First Amendment currently only protects the right of third-party publishers to print books, newsletters, websites, etc. on every aspect of these substances, including opinions, speculations, etc. Many manufacturers and suppliers also provide publications, but because they are also marketing the substances, they are subject to the monitoring and enforcement efforts of the Federal Trade Commission (FTC) which has jurisdiction over false claims made by marketers in public media. What constitutes the difference between truthful and false claims is hotly debated and is a central controversy in this arena.
Proposed strategies of life extension
Raymond Kurzweil, a futurist and transhumanist, believes that advanced medical nanorobotics could completely cure aging by 2030. According to Kurzweil, applying successive anti-aging methods as they become available could allow individuals to live long enough to benefit from a complete cure to aging once it is developed.
Cloning and body part replacement
Some life extensionists suggest that therapeutic cloning and stem cell research could one day provide a way to generate cells, body parts, or even entire bodies (generally referred to as reproductive cloning) that would be genetically identical to a prospective patient. In one experiment, a functioning dog's bladder was grown and proved to be viable after implantation. Recently, the US Department of Defense initiated a program to research the possibility of growing human body parts on mice. Complex biological structures, such as mammalian joints and limbs, have not yet been made. In one popular scenario, an individual's brain is transplanted from his or her aging body into a new, youthful body cloned from his or her own tissues. Dog and primate brain transplantation experiments were conducted in the mid-20th century but failed due to rejection and the inability to restore nerve connections. Proponents of body part replacement and cloning contend that the required biotechnologies are likely to appear earlier th
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