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Life Extension seeks methods to slow or halt aging, and if possible repair existing age-induced damage. "To die young at an old age" is the optimum goal. The mission is to extend the active, healthy years, not just to add more time to live in age-induced disability. There are several different schools of thought on how to best extend and enhance human life. Each takes a completely different approach in dealing with human aging, although they are all complementary and can be used simultaneously.

Those who feel that life extension is an impossible goal should consider the fact the normal human lifespan has already been extended far beyond its "natural" limits. After all, humans spent most of their history living as hunter-gatherers in stone age conditions, without modern medicine or large-scale environmental modifications. Under these harsh environmental conditions, most humans died in infancy, and the few survivors often succumbed to attack by predators, warfare, disease or famine before ever having a chance to die of old age. Even with a tribal support structure to maintain the elderly, humans were considered to lucky to have reached a ripe old age if they achieved the biblical "threescore years and ten", or 70 years.

Human life expectancy was greatly improved by the introduction of modern plumbing and access to clean water, better housing and medical care, and modern agricultural methods. Infant and maternal mortality plummeted, and in the western world lifespans increased enormously. Average life expectancy for Americans in 1900 was only 48 years for males, and 51 for females, according to the National Center for Health Statistics. In 2003, it was 75.4 for men, 80.5 for women. Obviously, great progress has already been made in extending human life.

However, many of the people who live this long suffer from chronic disabilities which remove much of the joy from those extra years; most of the elderly have some degree of arthritis, and 1/4 of people over 80 exhibit some signs of dementia. Often the medicine cabinets of the elderly bulge with medications; "polypharmacy", defined as the issuing of multiple, often conflicting prescription drugs to the same patient, is rife among elderly patients. The application of conventional western medicine, much of which aims to correct only the manifestations of disease rather than its underlying causes, may be reaching the point of diminishing returns.

Human aging occurs due to environmental factors, such as oxidative damage by free radicals, and also by pre-programmed cell death due to depletion of telomeres at the end of chromosomes. Theoretically, lifespan can be extended by preventing oxidative damage, helping the body to heal it, or changing the genetic code.

The most basic form of life extension is simply a modification of the individual's lifestyle. A good diet, regular exercise and avoidance of cigarettes provide a proven, well-tested benefit to health and life expectancy, compared to other methods for which no long-term scientific data is available.

Extreme caloric restriction is another option, albeit one that is unappealing to most people. However, it is a proven and reliable way to extend life expectancy of a large variety of animals using wild type strains of animals (ie avoiding the use of inbred lab strains that have special health problems). It had been known since the work of Clive McCay in the 1930s that calorie restriction can extend the maximum lifespan of rodents. This work was furthered by researchers Dr. Roy Walford and his student Dr. Richard Weindruch. In 1983, Dr. Walford published a book on this theory called Maximum Lifespan.

The benefits of caloric restriction may lie in its ability to reduce accumulation of genetic damage. The hearts of mice on the low-calorie diets showed nearly 20% fewer age-related genetic changes and also less DNA damage than those of mice on regular diets. Restricting calories also inhibited potentially disease-causing changes in the immune system, and even suppressed apoptosis, or programmed cell death.

Numerous studies on animals have shown nutritious diets low in calories can result in significant health benefits, slow ageing and extend longevity. In some cases, the life-spans of experimental animals increased by as much as a third. Caloric restriction shows benefits even when started late in life. Even when calorie intake was not restricted until middle age, the life-span of mice increased by 20 per cent. In an interview with WebMd, professor of genetics Tomas Prolla, PhD, stated, "Based on our finding, it appears that if people reduce their current calorie intake between 20 and 40% -- even starting in middle age -- they may delay the development of heart disease or possibly even prevent it."

Another natural form of life extension is the prevention of ongoing daily damage by free radicals through the consumption of antioxidants. The pioneer of this method was Linus Pauling, who consumed megadoses of vitamin C, one of the earliest known antioxidants. Aside from vitamin C, there are a multitude of antioxidants on the market, and more are being discovered currently. However, there is no one supplement that will cure every age-related ailment; all antioxidants work in conjunction with each other. Since scientists have not yet discovered all antioxidants, in addition to taking supplements people are advised to eat a diet rich in fruits and vegetables, the main source of these compounds.

Though scientific studies are not completely consistent, many show good results in preventing and treating diseases with antioxidants, such as vitamin E, one well-researched example. Vitamin E helps immune function, slows the progression of Alzheimer's disease and prevent cataracts and macular degeneration. In the Nurses* Health Study, involving more than 87,000 women, Dr. Meir Stampfer and colleagues at Harvard Medical School and the Harvard School of Public Health reported a 41 percent reduction in risk of heart disease among nurses who had taken vitamin E for more than two years. Many studies show that vitamin E also decreases the incidence of multiple types of cancer.

Some other well-known antioxidants, each with slightly different biological actions, are alpha-lipoic acid, beta-carotene, lycopene, pyconogenol, selenium and polyphenols found in red wine, cocoa and green tea.

However, even if free radical damage can be repaired entirely, humans reach the end of their biologically programmed lifespan at 125-135 years. To bypass this limitation, genetic engineering must be used. Scientists have identified many genes controlling aging in both animals and humans, and some animal studies have shown positive results. So far no tests have been done in humans, and it may be difficult to do since there are hundreds of genes linked to aging, and not one central "master switch".

Stem cells show promise of healing damaged tissues. If injected into a damaged organ, they have the ability to migrate exactly to where they are need to regrow diseased tissue. Stem cell therapies are being used on a small scale, mostly outside the US, and no large-scale studies have been done to examine their rate of effectiveness. For instance, famous singer Don Ho went to Thailand in 2005 for stem cell treatment for heart failure. The procedure Ho underwent was developed by TheraVitae Co., which has offices in Thailand and laboratories in Israel, where Ho's stem cells were sent to be multiplied. As of the date of this article, a clinical trial is about to start in Oregon in which stem cells will be used to treat Batten disease, a genetic brain disorder.

Transhumanism seeks to surpass the limits of the human body by doing away with it altogether, and replacing natural organs with technological machines. This has already been done widely for decades as a quality-of-life enhancement for arthritis patients who get knees and hips replaced. Intraocular implants of plastic lenses for cataract patients and artificial heart valves are other examples of inorganic devices being used to replace failing biological organ systems.

The most extreme version of transhumanism is Mind Uploading, the transfer of the entire human mind to a more durable material vessel such as a silicon computer. One proponent, futurist Ray Kurzweil, predicts that computer hardware will be powerful enough to run a functional model of the human mind by the 2020s. Uploading the human mind to a computer would potentially greatly extend human lifespan due to the ability to construct highly durable computer hardware and due to the potential to copy or transfer the mind to multiple computers.

Two objections are frequently raised to the transhumanist approach. One is that it would create less-than-human creatures, much like the Borg on Star Trek, cyborgs with few human qualities. Another problem is that machines, unlike biological systems, cannot heal themselves and must be replaced with new machine parts as old ones wear out. For instance, artificial hips implanted in the 1980s lasted 10-15 years, hips 15-20 years. However, use of improved materials such as ceramic instead of metal and plastic may allow current models to last much longer before revision surgery is needed.

If all else fails, Cryonics is based on the possibility that people who die today of some incurable disease may be revived in the future when a cure is available. So far, no frozen mammal has been successfully thawed; it is unknown whether it will ever be possible to re-animate a body frozen by the methods used today.