Life extension

Life extension is the idea of extending the human lifespan, either modestly – through improvements in medicine – or dramatically by increasing the maximum lifespan beyond its generally settled limit of 125 years. The ability to achieve such dramatic changes, however, does not currently exist.'simply to covet a prolonged life span for ourselves is both a sign and a cause of our failure to open ourselves to procreation and to any higher purpose ... desire to prolong youthfulness is not only a childish desire to eat one's life and keep it; it is also an expression of a childish and narcissistic wish incompatible with devotion to posterity.' Life extension is the idea of extending the human lifespan, either modestly – through improvements in medicine – or dramatically by increasing the maximum lifespan beyond its generally settled limit of 125 years. The ability to achieve such dramatic changes, however, does not currently exist. Some researchers in this area, and 'life extensionists', 'immortalists' or 'longevists' (those who wish to achieve longer lives themselves), believe that future breakthroughs in tissue rejuvenation, stem cells, regenerative medicine, molecular repair, gene therapy, pharmaceuticals, and organ replacement (such as with artificial organs or xenotransplantations) will eventually enable humans to have indefinite lifespans (agerasia) through complete rejuvenation to a healthy youthful condition. The ethical ramifications, if life extension becomes a possibility, are debated by bioethicists. The sale of purported anti-aging products such as supplements and hormone replacement is a lucrative global industry. For example, the industry that promotes the use of hormones as a treatment for consumers to slow or reverse the aging process in the US market generated about $50 billion of revenue a year in 2009. The use of such products has not been proven to be effective or safe. During the process of aging, an organism accumulates damage to its macromolecules, cells, tissues, and organs. Specifically, aging is characterized as and thought to be caused by 'genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication.' Oxidation damage to cellular contents caused by free radicals is believed to contribute to aging as well. The longest documented human lifespan is 122 years, the case of Jeanne Calment who according to records was born in 1875 and died in 1997, whereas the maximum lifespan of a wildtype mouse, commonly used as a model in research on aging, is about three years. Genetic differences between humans and mice that may account for these different aging rates include differences in efficiency of DNA repair, antioxidant defenses, energy metabolism, proteostasis maintenance, and recycling mechanisms such as autophagy. The 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 chronic disease such as cancer or cardiovascular disease play an increasing role in mortality. Extension of expected lifespan can often be achieved by access to improved medical care, vaccinations, 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 by environmental factors. Widely recognized methods of extending maximum lifespan in model organisms such as nematodes, fruit flies, and mice include caloric restriction, gene manipulation, and administration of pharmaceuticals. Another technique uses evolutionary pressures such as breeding from only older members or altering levels of extrinsic mortality.Some animals such as hydra, planarian flatworms, and certain sponges, corals, and jellyfish do not die of old age and exhibit potential immortality. Much life extension research focuses on nutrition—diets or supplements— although there is little evidence that they have an effect. The many diets promoted by anti-aging advocates are often contradictory. In some studies calorie restriction has been shown to extend the life of mice, yeast, and rhesus monkeys. However, a more recent study did not find calorie restriction to improve survival in rhesus monkeys. In humans the long-term health effects of moderate caloric restriction with sufficient nutrients are unknown.