In the broader sense, ageing can refer to single cells within an organism which have ceased dividing cellular senescence or to the population of a species population ageing. In humans, ageing represents the accumulation of changes in a human being over time, encompassing physical , psychological , and social changes. Reaction time, for example, may slow with age, while knowledge of world events and wisdom may expand.
Ageing is among the greatest known risk factors for most human diseases : of the roughly , people who die each day across the globe, about two thirds die from age-related causes. The causes of ageing are uncertain; current theories are assigned to the damage concept, whereby the accumulation of damage such as DNA oxidation may cause biological systems to fail, or to the programmed ageing concept, whereby internal processes such as DNA methylation may cause ageing.
Programmed ageing should not be confused with programmed cell death apoptosis. Human beings and members of other species, especially animals, necessarily experience ageing and mortality. Fungi, too, can age. Early life forms on Earth, starting at least 3. Such organisms Prokaryotes , Protozoans , algae multiply by fission into daughter cells; thus do not age and are innately immortal.
The sexual organism could henceforth pass on some of its genetic material to produce new individuals and could itself become disposable with respect to the survival of its species. Even within humans and other mortal species, there are cells with the potential for immortality: cancer cells which have lost the ability to die when maintained in a cell culture such as the HeLa cell line,  and specific stem cells such as germ cells producing ova and spermatozoa.
A number of characteristic ageing symptoms are experienced by a majority or by a significant proportion of humans during their lifetimes. Dementia becomes more common with age. Furthermore, many types of memory decline with ageing , but not semantic memory or general knowledge such as vocabulary definitions, which typically increases or remains steady until late adulthood  see Ageing brain.
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Intelligence declines with age, though the rate varies depending on the type and may in fact remain steady throughout most of the lifespan, dropping suddenly only as people near the end of their lives. Individual variations in rate of cognitive decline may therefore be explained in terms of people having different lengths of life. Age can result in visual impairment , whereby non-verbal communication is reduced,  which can lead to isolation and possible depression.
Older adults, however, may not suffer depression as much as younger adults, and were paradoxically found to have improved mood despite declining physical health. A distinction can be made between "proximal ageing" age-based effects that come about because of factors in the recent past and "distal ageing" age-based differences that can be traced to a cause in a person's early life, such as childhood poliomyelitis. Ageing is among the greatest known risk factors for most human diseases. At present, researchers are only just beginning to understand the biological basis of ageing even in relatively simple and short-lived organisms such as yeast.
A model organism for studying of ageing is the nematode C. Thanks to its short lifespan of 2—3 weeks, our ability to easily perform genetic manipulations or to suppress gene activity with RNA interference , or other factors. The factors proposed to influence biological ageing  fall into two main categories, programmed and damage-related.
Programmed factors follow a biological timetable, perhaps one that might be a continuation of the one that regulates childhood growth and development. This regulation would depend on changes in gene expression that affect the systems responsible for maintenance, repair and defense responses. Damage-related factors include internal and environmental assaults to living organisms that induce cumulative damage at various levels. In a detailed review, Lopez-Otin and colleagues , who discuss ageing through the lens of the damage theory, propose nine metabolic "hallmarks" of ageing in various organisms but especially mammals: .
It is likely that most of these pathways affect ageing separately, because targeting them simultaneously leads to additive increases in lifespan. The rate of ageing varies substantially across different species, and this, to a large extent, is genetically based. For example, numerous perennial plants ranging from strawberries and potatoes to willow trees typically produce clones of themselves by vegetative reproduction and are thus potentially immortal, while annual plants such as wheat and watermelons die each year and reproduce by sexual reproduction.
In it was discovered that inactivation of only two genes in the annual plant Arabidopsis thaliana leads to its conversion into a potentially immortal perennial plant. Clonal immortality apart, there are certain species whose individual lifespans stand out among Earth's life-forms, including the bristlecone pine at years  or years,  invertebrates like the hard clam known as quahog in New England at years,  the Greenland shark at years,  various deep-sea tube worms at over years,  fish like the sturgeon and the rockfish , and the sea anemone  and lobster.
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In laboratory settings, researchers have demonstrated that selected alterations in specific genes can extend lifespan quite substantially in yeast and roundworms , less so in fruit flies and less again in mice. Some of the targeted genes have homologues across species and in some cases have been associated with human longevity. Caloric restriction substantially affects lifespan in many animals, including the ability to delay or prevent many age-related diseases.
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Notwithstanding the similarly low calorie intake, the diet composition differed between the two studies notably a high sucrose content in the Wisconsin study , and the monkeys have different origins India, China , initially suggesting that genetics and dietary composition, not merely a decrease in calories, are factors in longevity. In his book How and Why We Age , Hayflick says that caloric restriction may not be effective in humans, citing data from the Baltimore Longitudinal Study of Aging which shows that being thin does not favour longevity.
Once these factors are accounted for, the optimal body weight above age 65 corresponds to a leaner body mass index of 23 to Alternatively, the benefits of dietary restriction can also be found by changing the macro nutrient profile to reduce protein intake without any changes to calorie level, resulting in similar increases in longevity. The Mediterranean diet is credited with lowering the risk of heart disease and early death. The amount of sleep has an impact on mortality. People who live the longest report sleeping for six to seven hours each night. Physical exercise may increase life expectancy.
Ageing - Wikipedia
Avoidance of chronic stress as opposed to acute stress is associated with a slower loss of telomeres in most but not all studies,   and with decreased cortisol levels. The following drugs and interventions have been shown to slow or reverse the biological effects of ageing in animal models, but none has yet been proven to do so in humans. Evidence in both animals and humans suggests that resveratrol may be a caloric restriction mimetic.
As of [update] , metformin was under study for its potential effect on slowing ageing in the worm C. Rapamycin was first shown to extend lifespan in eukaryotes in by Powers et al. Of particular note, the treatment began in mice aged 20 months, the equivalent of 60 human years. Cancer geneticist Ronald A.
DePinho and his colleagues published research on mice where telomerase activity was first genetically removed. Then, after the mice had prematurely aged, they restored telomerase activity by reactivating the telomerase gene. As a result, the mice were rejuvenated: Shrivelled testes grew back to normal and the animals regained their fertility.
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Other organs, such as the spleen, liver, intestines and brain, recuperated from their degenerated state. However, activating telomerase in humans could potentially encourage the growth of tumours. Most known genetic interventions in C. As of [update] , the record for lifespan extension in C. However, the benefits may not be proportional; longevity gains are typically greater in C. One explanation for this is that mammals, being much longer-lived, already have many traits which promote lifespan. Some research effort is directed to slow ageing and extend healthy lifespan.
The US National Institute on Aging currently funds an intervention testing programme, whereby investigators nominate compounds based on specific molecular ageing theories to have evaluated with respect to their effects on lifespan and age-related biomarkers in outbred mice. Prizes for extending lifespan and slowing ageing in mammals exist. The Methuselah Foundation offers the Mprize. It is a research incentive prize to encourage teams from all over the world to compete in an all-out effort to "hack the code" that regulates our health and lifespan.
It was founded by Joon Yun. Different cultures express age in different ways. The age of an adult human is commonly measured in whole years since the day of birth. Arbitrary divisions set to mark periods of life may include: juvenile via infancy , childhood , preadolescence , adolescence , early adulthood , middle adulthood , and late adulthood. More casual terms may include "teenagers," " tweens ," "twentysomething", "thirtysomething", etc. Most legal systems define a specific age for when an individual is allowed or obliged to do particular activities.
These age specifications include voting age , drinking age , age of consent , age of majority , age of criminal responsibility , marriageable age , age of candidacy , and mandatory retirement age.
Admission to a movie for instance, may depend on age according to a motion picture rating system. A bus fare might be discounted for the young or old. Each nation, government and non-governmental organisation has different ways of classifying age. In other words, chronological ageing may be distinguished from "social ageing" cultural age-expectations of how people should act as they grow older and "biological ageing" an organism's physical state as it ages. Population ageing is the increase in the number and proportion of older people in society.
Population ageing has three possible causes: migration, longer life expectancy decreased death rate and decreased birth rate. Ageing has a significant impact on society. Young people tend to have fewer legal privileges if they are below the age of majority , they are more likely to push for political and social change, to develop and adopt new technologies, and to need education.
Older people have different requirements from society and government, and frequently have differing values as well, such as for property and pension rights. In the 21st century, one of the most significant population trends is ageing. Consequently, fertility rates have continued to decline and life expectancy has risen. Life expectancy at birth is over 80 now in 33 countries.
Ageing is a "global phenomenon," that is occurring fastest in developing countries, including those with large youth populations, and poses social and economic challenges to the work which can be overcome with "the right set of policies to equip individuals, families and societies to address these challenges and to reap its benefits. As life expectancy rises and birth rates decline in developed countries, the median age rises accordingly.
According to the United Nations , this process is taking place in nearly every country in the world. Older people generally incur more health-related costs than do younger people in the workplace and can also cost more in worker's compensation and pension liabilities. In the United States for instance, the Bureau of Labor Statistics estimates that one in four American workers will be 55 or older by Among the most urgent concerns of older persons worldwide is income security.
This poses challenges for governments with ageing populations to ensure investments in pension systems continues in order to provide economic independence and reduce poverty in old age. These challenges vary for developing and developed countries. UNFPA stated that, "Sustainability of these systems is of particular concern, particularly in developed countries, while social protection and old-age pension coverage remain a challenge for developing countries, where a large proportion of the labour force is found in the informal sector.
The global economic crisis has increased financial pressure to ensure economic security and access to health care in old age. In order to elevate this pressure "social protection floors must be implemented in order to guarantee income security and access to essential health and social services for all older persons and provide a safety net that contributes to the postponement of disability and prevention of impoverishment in old age. It has been argued that population ageing has undermined economic development. Due to increasing share of the elderly in the population, health care expenditures will continue to grow relative to the economy in coming decades.
This has been considered as a negative phenomenon and effective strategies like labour productivity enhancement should be considered to deal with negative consequences of ageing.