Maximum life span (or, for humans, maximum reported age at death) is a measure of the maximum amount of time one or more members of a population have been observed to survive between birth and death. The term can also denote an estimate of the maximum amount of time that a member of a given species could survive between birth and death, provided circumstances that are optimal to that member's longevity.
Most living species have an upper limit on the number of times somatic cells not expressing telomerase can divide. This is called the Hayflick limit, although this number of cell divisions does not strictly control lifespan.
In animal studies, maximum span is often taken to be the mean life span of the most long-lived 10% of a given cohort. By another definition, however, maximum life span corresponds to the age at which the oldest known member of a species or experimental group has died. Calculation of the maximum life span in the latter sense depends upon the initial sample size. [1]
Maximum life span contrasts with mean life span (average life span , life expectancy), and longevity . Mean life span varies with susceptibility to disease, accident, suicide and homicide, whereas maximum life span is determined by "rate of aging". [2] [3] [ failed verification ] Longevity refers only to the characteristics of the especially long lived members of a population, such as infirmities as they age or compression of morbidity , and not the specific life span of an individual.
The longest living person whose dates of birth and death were verified according to the modern norms of Guinness World Records and the Gerontology Research Group was Jeanne Calment (1875–1997), a Frenchwoman who is verified to have lived to 122. The oldest male lifespan has only been verified as 116, by Japanese man Jiroemon Kimura. Reduction of infant mortality has accounted for most of the increased average life span longevity, but since the 1960s mortality rates among those over 80 years have decreased by about 1.5% per year. "The progress being made in lengthening lifespans and postponing senescence is entirely due to medical and public-health efforts, rising standards of living, better education, healthier nutrition and more salubrious lifestyles." [4] Animal studies suggest that further lengthening of median human lifespan as well as maximum lifespan could be achieved through "calorie restriction mimetic" drugs or by directly reducing food consumption. [5] Although calorie restriction has not been proven to extend the maximum human life span as of 2014 [update] , results in ongoing primate studies have demonstrated that the assumptions derived from rodents are valid in primates. [6] [7]
It has been proposed that no fixed theoretical limit to human longevity is apparent today. [8] [9] Studies in the biodemography of human longevity indicate a late-life mortality deceleration law: that death rates level off at advanced ages to a late-life mortality plateau. That is, there is no fixed upper limit to human longevity, or fixed maximal human lifespan. [10] This law was first quantified in 1939, when researchers found that the one-year probability of death at advanced age asymptotically approaches a limit of 44% for women and 54% for men. [11]
However, this evidence depends on the existence of a late-life plateaus and deceleration that can be explained, in humans and other species, by the existence of very rare errors. [12] [13] Age-coding error rates below 1 in 10,000 are sufficient to make artificial late-life plateaus, and errors below 1 in 100,000 can generate late-life mortality deceleration. These error rates cannot be ruled out by examining documents [13] (the standard) because of successful pension fraud, identity theft, forgeries and errors that leave no documentary evidence. This capacity for errors to explain late-life plateaus solves the "fundamental question in aging research is whether humans and other species possess an immutable life-span limit" and suggests that a limit to human life span exists. [14] A theoretical study suggested the maximum human lifespan to be around 125 years using a modified stretched exponential function for human survival curves. [15] In another study, researchers claimed that there exists a maximum lifespan for humans, and that the human maximal lifespan has been declining since the 1990s. [16] A theoretical study also suggested that the maximum human life expectancy at birth is limited by the human life characteristic value δ, which is around 104 years. [17]
In 2017, the United Nations conducted a Bayesian sensitivity analysis of global population burden based on life expectancy projection at birth in future decades. The 95% prediction interval of average life expectancy rises as high as 106 years old by 2090, with ongoing and layered effects on world population and demography should that happen. However, the prediction interval is extremely wide. [18]
Evidence for maximum lifespan is also provided by the dynamics of physiological indices with age. For example, scientists have observed that a person's VO2max value (a measure of the volume of oxygen flow to the cardiac muscle) decreases as a function of age. Therefore, the maximum lifespan of a person could be determined by calculating when the person's VO2max value drops below the basal metabolic rate necessary to sustain life, which is approximately 3 ml per kg per minute. [19] [ page needed ] On the basis of this hypothesis, athletes with a VO2max value between 50 and 60 at age 20 would be expected "to live for 100 to 125 years, provided they maintained their physical activity so that their rate of decline in VO2max remained constant". [20]
Small animals such as birds and squirrels rarely live to their maximum life span, usually dying of accidents, disease or predation.
The maximum life span of most species is documented in the AnAge repository (The Animal Ageing and Longevity Database). [22]
Maximum life span is usually longer for species that are larger, at least among endotherms, [23] or have effective defenses against predation, such as bat or bird flight, [24] arboreality, [25] chemical defenses [26] or living in social groups. [27] Among mammals, the presence of a caecal appendix is also correlated with greater maximal longevity. [28]
The differences in life span between species demonstrate the role of genetics in determining maximum life span ("rate of aging"). The records (in years) are these:
The longest-lived vertebrates have been variously described as
Invertebrate species which continue to grow as long as they live (e.g., certain clams, some coral species) can on occasion live hundreds of years:
Plants are referred to as annuals which live only one year, biennials which live two years, and perennials which live longer than that. The longest-lived perennials, woody-stemmed plants such as trees and bushes, often live for hundreds and even thousands of years (one may question whether or not they may die of old age). A giant sequoia, General Sherman, is alive and well in its third millennium. A Great Basin Bristlecone Pine called Methuselah is 4,856 years old. [55] Another Bristlecone Pine called Prometheus was a little older still, showing 4,862 years of growth rings. The exact age of Prometheus, however, remains unknown as it is likely that growth rings did not form every year due to the harsh environment in which it grew but it was estimated to be ~4,900 years old when it was cut down in 1964. [56] The oldest known plant (possibly oldest living thing) is a clonal Quaking Aspen ( Populus tremuloides ) tree colony in the Fishlake National Forest in Utah called Pando at about 16,000 years. Lichen, a symbiotic algae and fungal proto-plant, such as Rhizocarpon geographicum can live upwards of 10,000 years.
"Maximum life span" here means the mean life span of the most long-lived 10% of a given cohort. Caloric restriction has not yet been shown to break mammalian world records for longevity. Rats, mice, and hamsters experience maximum life-span extension from a diet that contains all of the nutrients but only 40–60% of the calories that the animals consume when they can eat as much as they want. Mean life span is increased 65% and maximum life span is increased 50%, when caloric restriction is begun just before puberty. [57] For fruit flies the life extending benefits of calorie restriction are gained immediately at any age upon beginning calorie restriction and ended immediately at any age upon resuming full feeding. [58]
Most biomedical gerontologists believe that biomedical molecular engineering will eventually extend maximum lifespan and even bring about rejuvenation. [59] Anti-aging drugs are a potential tool for extending life. [60]
Aubrey de Grey, a theoretical gerontologist, has proposed that aging can be reversed by strategies for engineered negligible senescence. De Grey has established The Methuselah Mouse Prize to award money to researchers who can extend the maximum life span of mice. So far, three Mouse Prizes have been awarded: one for breaking longevity records to Dr. Andrzej Bartke of Southern Illinois University (using GhR knockout mice); one for late-onset rejuvenation strategies to Dr. Stephen Spindler of the University of California (using caloric restriction initiated late in life); and one to Dr. Z. Dave Sharp for his work with the pharmaceutical rapamycin. [61]
Accumulated DNA damage appears to be a limiting factor in the determination of maximum life span. The theory that DNA damage is the primary cause of aging, and thus a principal determinant of maximum life span, has attracted increased interest in recent years. This is based, in part, on evidence in humans and mice that inherited deficiencies in DNA repair genes often cause accelerated aging. [62] [63] [64] There is also substantial evidence that DNA damage accumulates with age in mammalian tissues, such as those of the brain, muscle, liver, and kidney (reviewed by Bernstein et al. [65] and see DNA damage theory of aging and DNA damage (naturally occurring)). One expectation of the theory (that DNA damage is the primary cause of aging) is that among species with differing maximum life spans, the capacity to repair DNA damage should correlate with lifespan. The first experimental test of this idea was by Hart and Setlow [66] who measured the capacity of cells from seven different mammalian species to carry out DNA repair. They found that nucleotide excision repair capability increased systematically with species longevity. This correlation was striking and stimulated a series of 11 additional experiments in different laboratories over succeeding years on the relationship of nucleotide excision repair and life span in mammalian species (reviewed by Bernstein and Bernstein [67] ). In general, the findings of these studies indicated a good correlation between nucleotide excision repair capacity and life span. The association between nucleotide excision repair capability and longevity is strengthened by the evidence that defects in nucleotide excision repair proteins in humans and rodents cause features of premature aging, as reviewed by Diderich. [63]
Further support for the theory that DNA damage is the primary cause of aging comes from study of Poly ADP ribose polymerases (PARPs). PARPs are enzymes that are activated by DNA strand breaks and play a role in DNA base excision repair. Burkle et al. reviewed evidence that PARPs, and especially PARP-1, are involved in maintaining mammalian longevity. [68] The life span of 13 mammalian species correlated with poly(ADP ribosyl)ation capability measured in mononuclear cells. Furthermore, lymphoblastoid cell lines from peripheral blood lymphocytes of humans over age 100 had a significantly higher poly(ADP-ribosyl)ation capability than control cell lines from younger individuals.
Human life expectancy is a statistical measure of the estimate of the average remaining years of life at a given age. The most commonly used measure is life expectancy at birth. This can be defined in two ways. Cohort LEB is the mean length of life of a birth cohort and can be computed only for cohorts born so long ago that all their members have died. Period LEB is the mean length of life of a hypothetical cohort assumed to be exposed, from birth through death, to the mortality rates observed at a given year. National LEB figures reported by national agencies and international organizations for human populations are estimates of period LEB.
A telomere is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Telomeres are a widespread genetic feature most commonly found in eukaryotes. In most, if not all species possessing them, they protect the terminal regions of chromosomal DNA from progressive degradation and ensure the integrity of linear chromosomes by preventing DNA repair systems from mistaking the very ends of the DNA strand for a double-strand break.
Mitochondrial DNA is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in a eukaryotic cell; most of the DNA is in the cell nucleus, and, in plants and algae, the DNA also is found in plastids, such as chloroplasts.
Senescence or biological aging is the gradual deterioration of functional characteristics in living organisms. Whole organism senescence involves an increase in death rates or a decrease in fecundity with increasing age, at least in the later part of an organism's life cycle. However, the resulting effects of senescence can be delayed. The 1934 discovery that calorie restriction can extend lifespans by 50% in rats, the existence of species having negligible senescence, and the existence of potentially immortal organisms such as members of the genus Hydra have motivated research into delaying senescence and thus age-related diseases. Rare human mutations can cause accelerated aging diseases.
Life extension is the concept of extending the human lifespan, either modestly through improvements in medicine or dramatically by increasing the maximum lifespan beyond its generally-settled biological limit of around 125 years. Several researchers in the area, along with "life extensionists", "immortalists", or "longevists", postulate that future breakthroughs in tissue rejuvenation, stem cells, regenerative medicine, molecular repair, gene therapy, pharmaceuticals, and organ replacement will eventually enable humans to have indefinite lifespans through complete rejuvenation to a healthy youthful condition (agerasia). The ethical ramifications, if life extension becomes a possibility, are debated by bioethicists.
Longevity may refer to especially long-lived members of a population, whereas life expectancy is defined statistically as the average number of years remaining at a given age. For example, a population's life expectancy at birth is the same as the average age at death for all people born in the same year.
The naked mole-rat, also known as the sand puppy, is a burrowing rodent native to the Horn of Africa and parts of Kenya, notably in Somali regions. It is closely related to the blesmols and is the only species in the genus Heterocephalus.
The DAF-2 gene encodes for the insulin-like growth factor 1 (IGF-1) receptor in the worm Caenorhabditis elegans. DAF-2 is part of the first metabolic pathway discovered to regulate the rate of aging. DAF-2 is also known to regulate reproductive development, resistance to oxidative stress, thermotolerance, resistance to hypoxia, and resistance to bacterial pathogens. Mutations in DAF-2 and also Age-1 have been shown by Cynthia Kenyon to double the lifespan of the worms. In a 2007 episode of WNYC’s Radiolab, Kenyon called DAF-2 "the grim reaper gene.”
Biogerontology is the sub-field of gerontology concerned with the biological aging process, its evolutionary origins, and potential means to intervene in the process. The term "biogerontology" was coined by S. Rattan, and came in regular use with the start of the journal Biogerontology in 2000. It involves interdisciplinary research on the causes, effects, and mechanisms of biological aging. Biogerontologist Leonard Hayflick has said that the natural average lifespan for a human is around 92 years and, if humans do not invent new approaches to treat aging, they will be stuck with this lifespan. James Vaupel has predicted that life expectancy in industrialized countries will reach 100 for children born after the year 2000. Many surveyed biogerontologists have predicted life expectancies of more than three centuries for people born after the year 2100. Other scientists, more controversially, suggest the possibility of unlimited lifespans for those currently living. For example, Aubrey de Grey offers the "tentative timeframe" that with adequate funding of research to develop interventions in aging such as strategies for engineered negligible senescence, "we have a 50/50 chance of developing technology within about 25 to 30 years from now that will, under reasonable assumptions about the rate of subsequent improvements in that technology, allow us to stop people from dying of aging at any age". The idea of this approach is to use presently available technology to extend lifespans of currently living humans long enough for future technological progress to resolve any remaining aging-related issues. This concept has been referred to as longevity escape velocity.
Enquiry into the evolution of ageing, or aging, aims to explain why a detrimental process such as ageing would evolve, and why there is so much variability in the lifespans of organisms. The classical theories of evolution suggest that environmental factors, such as predation, accidents, disease, and/or starvation, ensure that most organisms living in natural settings will not live until old age, and so there will be very little pressure to conserve genetic changes that increase longevity. Natural selection will instead strongly favor genes which ensure early maturation and rapid reproduction, and the selection for genetic traits which promote molecular and cellular self-maintenance will decline with age for most organisms.
Leonard Pershing Guarente is an American biologist best known for his research on life span extension in the budding yeast Saccharomyces cerevisiae, roundworms, and mice. He is a Novartis Professor of Biology at the Massachusetts Institute of Technology.
Sirtuin 1, also known as NAD-dependent deacetylase sirtuin-1, is a protein that in humans is encoded by the SIRT1 gene.
Sirtuin 6 is a stress responsive protein deacetylase and mono-ADP ribosyltransferase enzyme encoded by the SIRT6 gene. In laboratory research, SIRT6 appears to function in multiple molecular pathways related to aging, including DNA repair, telomere maintenance, glycolysis and inflammation. SIRT6 is member of the mammalian sirtuin family of proteins, which are homologs to the yeast Sir2 protein.
The DNA damage theory of aging proposes that aging is a consequence of unrepaired accumulation of naturally occurring DNA damage. Damage in this context is a DNA alteration that has an abnormal structure. Although both mitochondrial and nuclear DNA damage can contribute to aging, nuclear DNA is the main subject of this analysis. Nuclear DNA damage can contribute to aging either indirectly or directly.
The anti-aging movement is a social movement devoted to eliminating or reversing aging, or reducing the effects of it. A substantial portion of the attention of the movement is on the possibilities for life extension, but there is also interest in techniques such as cosmetic surgery which ameliorate the effects of aging rather than delay or defeat it.
Genetics of aging is generally concerned with life extension associated with genetic alterations, rather than with accelerated aging diseases leading to reduction in lifespan.
In biogerontology, the disposable soma theory of aging states that organisms age due to an evolutionary trade-off between growth, reproduction, and DNA repair maintenance. Formulated by British biologist Thomas Kirkwood, the disposable soma theory explains that an organism only has a limited amount of resources that it can allocate to its various cellular processes. Therefore, a greater investment in growth and reproduction would result in reduced investment in DNA repair maintenance, leading to increased cellular damage, shortened telomeres, accumulation of mutations, compromised stem cells, and ultimately, senescence. Although many models, both animal and human, have appeared to support this theory, parts of it are still controversial. Specifically, while the evolutionary trade-off between growth and aging has been well established, the relationship between reproduction and aging is still without scientific consensus, and the cellular mechanisms largely undiscovered.
The mitochondrial theory of ageing has two varieties: free radical and non-free radical. The first is one of the variants of the free radical theory of ageing. It was formulated by J. Miquel and colleagues in 1980 and was developed in the works of Linnane and coworkers (1989). The second was proposed by A. N. Lobachev in 1978.
This timeline lists notable events in the history of research into senescence or biological aging, including the research and development of life extension methods, brain aging delay methods and rejuvenation.
Longevity Quotient (LQ) is a simplified measure to enable normalized comparisons of various species' longevity. It shares some similarity with measures such as Intelligence Quotient. It originated with Steven N. Austad and Kathleen E Fischer's 1991 paper on mammalian aging.
The oldest cat ever was Creme Puff, who was born on August 3, 1967, and lived until August 6, 2005—38 years and 3 days in total.
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