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Life expectancy is a statistical measure of the average time an organism is expected to live, based on the year of its birth, its current age, and other
demographic Demography (from prefix ''demo-'' from Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period ...

demographic
factors like sex. The most commonly used measure is life expectancy at birth (LEB), which can be defined in two ways. ''Cohort'' LEB is the mean length of life of a birth
cohort Cohort or cohortes may refer to: * Cohort (educational group), a group of students working together through the same academic curriculum * Cohort (floating point), a set of different encodings of the same numerical value * Cohort (military unit), ...
(all individuals born in a given year) 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 A hypothesis (plural hypotheses) is a proposed explanation An explanation is a set of statements usually constructed to describe a set of facts which clarifies the causes, context Context may refer to: * Context (language use), the rel ...
cohort assumed to be exposed, from birth through death, to the
mortality rate Mortality rate, or death rate, is a measure of the number of death Death is the permanent, irreversible cessation of all biological functions that sustain a living Living or The Living may refer to: Common meanings *Life, a conditi ...
s observed at a given year. National LEB figures reported by national agencies and international organizations for human populations are estimates of ''period'' LEB. In the
Bronze Age The Bronze Age is a prehistoric Periodization, period that was characterized by the use of bronze, in some areas proto-writing, and other early features of urban civilization. The Bronze Age is the second principal period of the Three-age sys ...
and the
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory Prehistory, also known as pre-literary history, is the period of human history Human history, or world history, is the narrative of Human, humanity's pa ...
, human LEB was 26 years; the 2010 world LEB was 67.2 years. In recent years, LEB in
Eswatini (Swaziland) Eswatini ( ; ss, eSwatini ), officially the Kingdom of Eswatini ( ss, Umbuso weSwatini, links=no), sometimes written in English as eSwatini, and formerly and still commonly known in English as Swaziland ( ; officially renamed in 2018), is a l ...

Eswatini (Swaziland)
is 49, while LEB in
Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an in ...

Japan
is 83. The combination of high
infant mortality Infant mortality is the death of young children under the age of 1. This death toll is measured by the infant mortality rate (IMR), which is the probability of deaths of children under one year of age per 1000 live births. The under-five mortali ...

infant mortality
and deaths in young adulthood from accidents, epidemics, plagues, wars, and childbirth, before modern medicine was widely available, significantly lowers LEB. For example, a society with a LEB of 40 would have relatively few people dying at exactly 40: most will die before 30 or after 55. In populations with high infant mortality rates, LEB is highly sensitive to the rate of death in the first few years of life. Because of this sensitivity, LEB can be grossly misinterpreted, leading to the belief that a population with a low LEB would have a small proportion of older people. A different measure, such as life expectancy at age 5 (e5), can be used to exclude the effect of infant mortality to provide a simple measure of overall mortality rates other than in early childhood. Aggregate population measures such as the proportion of the population in various age groups, are also used alongside individual-based measures like formal life expectancy when analyzing population structure and dynamics. However, pre-modern societies still had universally higher mortality rates and lower life expectancies at every age for both genders, and this example was relatively rare. In societies with life expectancies of 30, for instance, a 40-year remaining timespan at age 5 may not have been uncommon, but a 60-year one was. Until the middle of the 20th century, infant mortality was approximately 40–60% of the total mortality. Excluding child mortality, the average life expectancy during the 12th–19th centuries was approximately 55 years. If a medieval person survived childhood, they had about a 50% chance of living 50–55 years, instead of only 25–40 years. Mathematically, life expectancy is the mean number of years of life remaining at a given age. It is denoted by e_x, which is the mean number of subsequent years of life for someone at age x, with a particular
mortality Mortality is the state of being mortal, or susceptible to death (1906) Death is the permanent, Irreversible process, irreversible cessation of all biological process, biological functions that sustain a living organism. Brain death is some ...
. Life expectancy,
longevity The word "longevity The word "wikt:longevity, longevity" is sometimes used as a synonym for "life expectancy" in demography. However, the term ''longevity'' is sometimes meant to refer only to especially long-lived members of a population, ...
, and maximum lifespan are not synonymous. Longevity refers to the relatively long lifespan of some members of a population.
Maximum lifespan Maximum life span (or, for humans Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well a ...
is the age at death for the longest-lived individual of a species. Because life expectancy is an average, a particular person may die many years before or many years after the "expected" survival. Life expectancy is also used in plant or animal
ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms In biol ...
, and in
life table In actuarial science Actuarial science is the discipline that applies mathematical Mathematics (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic ...
s (also known as
actuarial Actuarial science is the discipline that applies mathematics, mathematical and statistics, statistical methods to Risk assessment, assess risk in insurance, finance, and other industries and professions. More generally, actuaries apply rigorous m ...
tables). The concept of life expectancy may also be used in the context of manufactured objects, though the related term
shelf life Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or just no longer ...
is commonly used for consumer products, and the terms "mean time to breakdown" (MTTB) and "
mean time between failures Mean time between failures (MTBF) is the predicted elapsed time between inherent failure Failure is the state or condition of not meeting a desirable or intended objective Objective may refer to: * Objective (optics), an element in a camera ...
" (MTBF) are used in engineering.


Human patterns


Maximum

Records of human lifespan above age 100 are highly susceptible to errors. For example, the previous world-record holder for human lifespan, Carrie White, was uncovered as a simple typographic error after more than two decades. The longest verified lifespan for any human is that of Frenchwoman
Jeanne Calment Jeanne Louise Calment (; 21 February 1875 – 4 August 1997) was a French supercentenarian and the oldest people, oldest human whose age is well-documented, with a lifespan of 122 years and 164 days. Her longevity attracted media attention and ...
, who is verified as having lived to age 122 years, 164 days, between 21 February 1875 and 4 August 1997. This is referred to as the "
maximum life span Maximum life span (or, for humans Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as ...
," which is the upper boundary of life, the maximum number of years any human is known to have lived.Santrock, John (2007). Life Expectancy. A Topical Approach to: Life-Span Development (pp. 128–132). New York, New York: The McGraw-Hill Companies, Inc. A theoretical study shows that the maximum life expectancy at birth is limited by the human life characteristic value δ, which is around 104 years. According to a study by biologists Bryan G. Hughes and Siegfried Hekimi, there is no evidence for limit on human lifespan. However, this view has been questioned on the basis of error patterns.


Variation over time

The following information is derived from the 1961 ''
Encyclopædia Britannica The (Latin for "British Encyclopaedia") is a general knowledge English-language encyclopaedia which is now published exclusively as an online encyclopedia, online encyclopaedia. It was formerly published by Encyclopædia Britannica, Inc., ...
'' and other sources, some with questionable accuracy. Unless otherwise stated, it represents estimates of the life expectancies of the
world population In demography, demographics, the world population is the total number of humans currently living, and was estimated to have exceeded 7.9 billion people . It took over 2 million years of prehistory, human prehistory and human history, history fo ...

world population
as a whole. In many instances, life expectancy varied considerably according to class and gender. Life expectancy at birth takes account of
infant mortality Infant mortality is the death of young children under the age of 1. This death toll is measured by the infant mortality rate (IMR), which is the probability of deaths of children under one year of age per 1000 live births. The under-five mortali ...

infant mortality
and
child mortality Child mortality is the mortality Mortality is the state of being mortal, or susceptible to death (1906) Death is the permanent, Irreversible process, irreversible cessation of all biological process, biological functions that sustain a ...

child mortality
but not prenatal mortality.
Life expectancy increases with age as the individual survives the higher mortality rates associated with childhood. For instance, the table gives the life expectancy at birth among 13th-century English nobles at 30. Having survived to the age of 21, a male member of the English aristocracy in this period could expect to live: *1200–1300: to age 64 *1300–1400: to age 45 (because of the
bubonic plague Bubonic plague is one of three types of plague caused by the plague bacterium Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell The cell (from Latin ''cella'', meaning "small room") is the basic ...
) *1400–1500: to age 69 *1500–1550: to age 71 17th-century English life expectancy was only about 35 years, largely because infant and child mortality remained high. Life expectancy was under 25 years in the early
Colony of Virginia , legislature = House of Burgesses (1619–1776) , today = , demonym = , area_km2=, area_rank=, GDP_PPP=, GDP_PPP_year=, HDI=, HDI_year= The Colony of Virginia, chartered in 1606 and settled in 1607, was ...
, and in seventeenth-century New England, about 40 percent died before reaching adulthood. During the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe Continental Europe or mainland Europe is the contiguous continent A continent is any of several large landmasse ...
, the life expectancy of children increased dramatically. The under-5 mortality rate in London decreased from 74.5% in 1730–1749 to 31.8% in 1810–1829.
Public health Public health has been defined as "the science and art of preventing disease", prolonging life and improving quality of life Quality of life (QOL) is defined by the World Health Organization The World Health Organization (WHO) is a s ...

Public health
measures are credited with much of the recent increase in life expectancy. During the 20th century, despite a brief drop due to the
1918 flu pandemic Spanish flu, also known as the Great Influenza epidemic or the 1918 influenza pandemic, was an exceptionally deadly global influenza pandemic An influenza pandemic is an epidemic An epidemic (from Ancient Greek, Greek ἐπί ''epi'' ...
starting around that time the average lifespan in the United States increased by more than 30 years, of which 25 years can be attributed to advances in public health. The life expectancy for people reaching adulthood is greater, — ignoring infant and child mortality. For instance,
16th Century The 16th century begins with the Julian calendar, Julian year 1501 (Roman numerals, MDI) and ends with either the Julian or the Gregorian calendar, Gregorian year 1600 (Roman numerals, MDC) (depending on the reckoning used; the Gregorian calend ...
English and Welsh women at 15 years may have had an life expectancy of around 35 more years (50 total).


Regional variations

Human beings are expected to live on average 30–40 years in
Eswatini Eswatini ( ; ss, eSwatini ), officially the Kingdom of Eswatini and formerly officially entitled (and still often known) in English as Swaziland ( ; officially renamed in 2018), is a landlocked country A landlocked country is a country ...

Eswatini
and 82.6 years in Japan, but the latter's recorded life expectancy may have been very slightly increased by counting many infant deaths as stillborn. An analysis published in 2011 in ''
The Lancet ''The Lancet'' is a weekly peer-reviewed Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ( peers). It functions as a form of self-regulation by qualified members of a prof ...
'' attributes Japanese life expectancy to
equal opportunities Equal opportunity is a state of fairness in which individuals are treated similarly, unhampered by artificial barriers or prejudices or preferences, except when particular distinctions can be explicitly justified. The intent is that the important jo ...
and
public health Public health has been defined as "the science and art of preventing disease", prolonging life and improving quality of life Quality of life (QOL) is defined by the World Health Organization The World Health Organization (WHO) is a s ...

public health
as well as diet. There are great variations in life expectancy between different parts of the world, mostly caused by differences in
public health Public health has been defined as "the science and art of preventing disease", prolonging life and improving quality of life Quality of life (QOL) is defined by the World Health Organization The World Health Organization (WHO) is a s ...

public health
, medical care, and diet. The impact of
AIDS Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection An infection is the invasion of an organism's body by , their multiplication, and the reaction of ...
on life expectancy is particularly notable in many African countries. According to projections made by the United Nations (UN) in 2002, the life expectancy at birth for 2010–2015 (if
HIV/AIDS Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection An infection is the invasion of an organism's body by , their multiplication, and the reaction of ...
did not exist) would have been: *70.7 years instead of 31.6 years, Botswana *69.9 years instead of 41.5 years, South Africa *70.5 years instead of 31.8 years, Zimbabwe Actual life expectancy in Botswana declined from 65 in 1990 to 49 in 2000 before increasing to 66 in 2011. In South Africa, life expectancy was 63 in 1990, 57 in 2000, and 58 in 2011. And in Zimbabwe, life expectancy was 60 in 1990, 43 in 2000, and 54 in 2011. During the last 200 years, African countries have generally not had the same improvements in mortality rates that have been enjoyed by countries in Asia, Latin America, and Europe. In the United States, African-American people have shorter life expectancies than their European-American counterparts. For example, white Americans born in 2010 are expected to live until age 78.9, but black Americans only until age 75.1. This 3.8-year gap, however, is the lowest it has been since 1975 at the latest. The greatest difference was 7.1 years in 1993."Deaths: Final Data for 2010", ''National Vital Statistics Reports'', authored by Sherry L. Murphy, Jiaquan Xu, and Kenneth D. Kochanek, volume 61, number 4, page 12, 8 May 2013
/ref> In contrast, Asian-American women live the longest of all ethnic groups in the United States, with a life expectancy of 85.8 years. The life expectancy of Hispanic Americans is 81.2 years. According to the new government reports in the US, life expectancy in the country dropped again because of the rise in suicide and drug overdose rates. The Centers for Disease Control (CDC) found nearly 70,000 more Americans died in 2017 than in 2016, with rising rates of death among 25- to 44-year-olds. Cities also experience a wide range of life expectancy based on neighborhood breakdowns. This is largely due to economic clustering and poverty conditions that tend to associate based on geographic location. Multi-generational poverty found in struggling neighborhoods also contributes. In United States cities such as
Cincinnati Cincinnati ( ) is a city in the U.S. state In the , a state is a , of which there are currently 50. Bound together in a , each state holds al jurisdiction over a separate and defined geographic territory where it shares its with the ...

Cincinnati
, the life expectancy gap between low income and high-income neighborhoods touches 20 years.


Economic circumstances

Economic circumstances also affect life expectancy. For example, in the United Kingdom, life expectancy in the wealthiest and richest areas is several years higher than in the poorest areas. This may reflect factors such as diet and lifestyle, as well as access to medical care. It may also reflect a selective effect: people with chronic life-threatening illnesses are less likely to become wealthy or to reside in affluent areas. In
Glasgow Glasgow ( ; sco, Glesga; gd, Glaschu) is the most populous city A city is a large .Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia'' ...

Glasgow
, the disparity is amongst the highest in the world: life expectancy for males in the heavily deprived Calton area stands at 54, which is 28 years less than in the affluent area of
Lenzie Lenzie () is an affluent town by the Edinburgh and Glasgow Railway in the East Dunbartonshire East Dunbartonshire ( sco, Aest Dunbartanshire; gd, Siorrachd Dhùn Bhreatainn an Ear) is one of the 32 council areas of Scotland. It borders the no ...
, which is the only 8 km away. A 2013 study found a pronounced relationship between
economic inequality There are wide varieties of economic inequality, most notably measured using the distribution of incomeIn economics Economics () is the social science that studies how people interact with value; in particular, the Production (econom ...
and life expectancy. However, a study by José A. Tapia Granados and Ana Diez Roux at the
University of Michigan , mottoeng = "Arts, Knowledge, Truth" , former_names = Catholepistemiad, or University of Michigania (1817–1821) , budget = $8.99 billion (2018) , endowment = $17 billion (2021)As of October 25, 2021. ...

University of Michigan
found that life expectancy actually increased during the
Great Depression The Great Depression was a severe worldwide economic depression An economic depression is a sustained, long-term downturn in economic activity in one or more economies. It is a more severe economic downturn than a economic recession, recess ...
, and during recessions and depressions in general. The authors suggest that when people are working at a more extreme degree during prosperous economic times, they undergo more stress, exposure to
pollution Pollution is the introduction of contaminant Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural en ...

pollution
, and the likelihood of injury among other longevity-limiting factors. Life expectancy is also likely to be affected by exposure to high levels of highway air pollution or industrial
air pollution Air pollution is the presence of substances in the atmosphere that are harmful to the health of humans and other Outline of life forms, living beings, or cause damage to the climate or to materials. There are different types of air pollutants, ...

air pollution
. This is one way that occupation can have a major effect on life expectancy. Coal miners (and in prior generations, asbestos cutters) often have lower life expectancies than average. Other factors affecting an individual's life expectancy are genetic disorders, drug use,
tobacco smoking Tobacco smoking is the practice of burning tobacco Tobacco is the common name of several plants in the ' of the , and the general term for any product prepared from the of these plants. of tobacco are known, but the chief commerci ...

tobacco smoking
, excessive alcohol consumption, obesity, access to health care, diet, and exercise.


Sex differences

In the present, female human life expectancy is greater than that of males, despite females having higher morbidity rates, see Health Survival paradox. There are many potential reasons for this. Traditional arguments tend to favor sociology-environmental factors: historically, men have generally consumed more
tobacco Tobacco is the common name of several plants in the genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defini ...

tobacco
,
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...
and
drug A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via insuffl ...

drug
s than women in most societies, and are more likely to die from many associated diseases such as
lung cancer Lung cancer, also known as lung carcinoma, since about 98–99% of all lung cancers are carcinomas, is a malignant lung tumor characterized by uncontrolled cell growth in tissue (biology), tissues of the lung. Lung carcinomas derive from trans ...

lung cancer
,
tuberculosis Tuberculosis (TB) is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the in ...

tuberculosis
and
cirrhosis of the liver Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis, due to damage caused by liver disease. Damage causes tissue repa ...
. Men are also more likely to die from injuries, whether unintentional (such as occupational,
war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (new ...

war
or
car accidents A traffic collision, also called a motor vehicle collision, car accident, or car crash, occurs when a vehicle A vehicle (from la, vehiculum) is a machine that transport Transport (commonly used in the U.K.), or transportation (used ...
) or intentional (
suicide Suicide is the act of intentionally causing one's own death Death is the permanent, irreversible cessation of all biological functions that sustain a living Living or The Living may refer to: Common meanings *Life, a condition t ...

suicide
). Men are also more likely to die from most of the leading causes of death (some already stated above) than women. Some of these in the United States include cancer of the respiratory system, motor vehicle accidents, suicide, cirrhosis of the liver, emphysema, prostate cancer, and coronary heart disease. These far outweigh the female mortality rate from breast cancer and cervical cancer. In the past, mortality rates for females in child-bearing age groups were higher than for males at the same age. A paper from 2015 found that female fetuses have a higher mortality rate than male fetuses. This finding contradicts papers dating from 2002 and earlier that attribute the male sex to higher in-utero mortality rates. Among the smallest premature babies (those under 2 pounds or 900 g), females have a higher survival rate. At the other extreme, about 90% of individuals aged 110 are female. The difference in life expectancy between men and women in the United States dropped from 7.8 years in 1979 to 5.3 years in 2005, with women expected to live to age 80.1 in 2005. Data from the UK shows the gap in life expectancy between men and women decreasing in later life. This may be attributable to the effects of infant mortality and young adult death rates. Some argue that shorter male life expectancy is merely another manifestation of the general rule, seen in all mammal species, that larger-sized individuals within a species tend, on average, to have shorter lives. This biological difference occurs because women have more resistance to infections and degenerative diseases. In her extensive review of the existing literature, Kalben concluded that the fact that women live longer than men was observed at least as far back as 1750 and that, with relatively equal treatment, today males in all parts of the world experience greater mortality than females. Kallen's study, however, was restricted to data in Western Europe alone, where the demographic transition occurred relatively early. United Nations statistics from mid-twentieth century onward, show that in all parts of the world, females have a higher life expectancy at age 60 than males. Of 72 selected causes of death, only 6 yielded greater female than male age-adjusted death rates in 1998 in the United States. Except for birds, for almost all of the animal species studied, males have higher mortality than females. Evidence suggests that the sex mortality differential in people is due to both biological/genetic and environmental/behavioral risk and protective factors. There is a recent suggestion that
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
l mutations that shorten lifespan continue to be expressed in males (but less so in females) because mitochondria are inherited only through the mother. By contrast,
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of peta ...
weeds out mitochondria that reduce female survival; therefore such mitochondria are less likely to be passed on to the next generation. This thus suggests that females tend to live longer than males. The authors claim that this is a partial explanation. In March 2020 researchers reported that their review supports the unguarded X hypothesis: according to this hypothesis one reason for why the average lifespan of males isn't as long as that of females––by 18% on average according to the study––is that they have a
Y chromosome The Y chromosome is one of two sex chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaper ...
which can't protect an individual from harmful genes expressed on the X chromosome, while a duplicate X chromosome, as present in female organisms, can ensure harmful genes aren't . Before the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe Continental Europe or mainland Europe is the contiguous continent A continent is any of several large landmasse ...
, men lived longer than women on average. In developed countries, starting around 1880, death rates decreased faster among women, leading to differences in mortality rates between males and females. Before 1880 death rates were the same. In people born after 1900, the death rate of 50- to 70-year-old men was double that of women of the same age. Men may be more vulnerable to cardiovascular disease than women, but this susceptibility was evident only after deaths from other causes, such as infections, started to decline. Most of the difference in life expectancy between the sexes is accounted for by differences in the rate of death by cardiovascular diseases among persons aged 50–70.


Genetics

In July
2020 2020 was heavily defined by the COVID-19 pandemic The COVID-19 pandemic is an ongoing global pandemic A pandemic (from , , "all" and , , "local people" the 'crowd') is an of an that has spread across a large region, for insta ...
, scientists, using public
biological data This is a list of file formats used by computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Comp ...
on 1.75 million people with known lifespans overall, identified 10 genomic loci which appear to intrinsically influence health span, lifespan, and longevity––of which half have not been reported previously at genome-wide significance and most being associated with
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped ...
––and identified haem metabolism as a promising candidate for further research within the field. Their study suggests that high levels of iron in the blood likely reduce, and genes involved in metabolising iron likely increase healthy years of life in humans. Text and images are available under
Creative Commons Attribution 4.0 International License


Centenarians

In developed countries, the number of centenarians is increasing at approximately 5.5% per year, which means doubling the centenarian population every 13 years, pushing it from some 455,000 in 2009 to 4.1  million in 2050. Japan is the country with the highest ratio of centenarians (347 for every 1  million inhabitants in September 2010).
Shimane Prefecture is a Prefectures of Japan, prefecture of Japan located in the Chūgoku region of Honshu. Shimane Prefecture is the List of Japanese prefectures by population, second-least populous prefecture of Japan at 665,205 (February 1, 2021) and has a geog ...
had an estimated 743 centenarians per million inhabitants. In the United States, the number of centenarians grew from 32,194 in 1980 to 71,944 in November 2010 (232 centenarians per million inhabitants).


Mental illness

Mental illness is reported to occur in approximately 18% of the average American population. The mentally ill have been shown to have a 10- to a 25-year reduction in life expectancy. Generally, the reduction of lifespan in the mentally ill population compared to the mentally stable population has been studied and documented. The greater mortality of people with mental disorders may be due to death from injury, from
co-morbid In medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment or Palliative care , palliation of their in ...
conditions, or medication side effects. For instance, psychiatric medications can increase the risk of developing
diabetes Diabetes mellitus, commonly known as just diabetes, is a group of metabolic disorder A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients such as proteins, fats, and carbohydrate ...
. It has been shown that the psychiatric medication olanzapine can increase risk of developing
agranulocytosis Agranulocytosis, also known as agranulosis or granulopenia, is an acute condition involving a severe and dangerous leukopenia Leukopenia () is a decrease in the number of leukocytes. Found in the blood, they are the white blood cells, and are the ...
among other comorbidities. Psychiatric medicines also affect the
gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, d ...
, where the mentally ill have a four times risk of gastrointestinal disease. As of the year 2020 and the
COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease A contagious disease is a disease A disease is a particular abnormal condition that negatively affects the structure A structure is an arrangement and organization o ...

COVID-19
pandemic, researchers have found an increased risk of death in the mentally ill.


Other illnesses

The life expectancy of people with diabetes, which is 9.3% of the U.S. population, is reduced by roughly ten to twenty years. People over 60 years old with
Alzheimer's disease Alzheimer's disease (AD), also referred to simply as Alzheimer's, is a neurodegenerative disease A neurodegenerative disease is caused by the progressive loss of structure or function of neuron A neuron or nerve cell is an membrane p ...
have about a 50% life expectancy of 3 to 10 years. Other demographics that tend to have a lower life expectancy than average include transplant recipients, and the obese.


Education

Education on all levels has been shown to be strongly associated with increased life expectancy. This association may be due partly to higher income, which can lead to increased life expectancy. Despite the association, there is no causal relationship between higher education and life expectancy. According to a paper from 2015, the mortality rate for the Caucasian population in the United States from 1993 to 2001 is four times higher for those who did not complete high school compared to those who have at least 16 years of education. In fact, within the U.S. adult population, those who have less than a high school education have the shortest life expectancies. Pre-school education also plays a large role in life expectancy. It was found that high-quality early-stage childhood education had positive effects on health. Researchers discovered this by analyzing the results of the Carolina Abecedarian Project (ABC) finding that the disadvantaged children who were randomly assigned to treatment had lower instances of risk factors for cardiovascular and metabolic diseases in their mid-30s.


Evolution and aging rate

Various species of plants and animals, including humans, have different lifespans. Evolutionary theory states that organisms that, by virtue of their defenses or lifestyle, live for long periods and avoid accidents, disease, predation, etc. are likely to have genes that code for slow aging, which often translates to good cellular repair. One theory is that if predation or accidental deaths prevent most individuals from living to an old age, there will be less natural selection to increase the intrinsic life span. That finding was supported in a classic study of opossums by Austad; however, the opposite relationship was found in an equally prominent study of guppies by Reznick. One prominent and very popular theory states that lifespan can be lengthened by a tight budget for food energy called
caloric restriction Calorie restriction (caloric restriction or energy restriction) is a Diet (nutrition), dietary regimen that reduces food intake without incurring malnutrition. "Reduce" can be defined relative to the subject's previous intake before intentionally r ...
. Caloric restriction observed in many animals (most notably mice and rats) shows a near doubling of life span from a very limited calorific intake. Support for the theory has been bolstered by several new studies linking lower basal metabolic rate to increased life expectancy. That is the key to why animals like giant
tortoise Tortoises () are reptiles Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a ...

tortoise
s can live so long. Studies of humans with life spans of at least 100 have shown a link to decreased thyroid activity, resulting in their lowered metabolic rate. In a broad survey of zoo animals, no relationship was found between investment of the animal in reproduction and its life span.


Calculation

The starting point for calculating life expectancy is the age-specific death rates of the population members. If a large amount of data is available, a
statistical population In statistics, a population is a Set (mathematics), set of similar items or events which is of interest for some question or experiment. A statistical population can be a group of existing objects (e.g. the set of all stars within the Milky Way ga ...
can be created that allow the age-specific death rates to be simply taken as the mortality rates actually experienced at each age (the number of deaths divided by the number of years "exposed to risk" in each data cell). However, it is customary to apply smoothing to iron out, as much as possible, the random statistical fluctuations from one year of age to the next. In the past, a very simple model used for this purpose was the
Gompertz function The Gompertz curve or Gompertz function is a type of mathematical model A mathematical model is a description of a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a ...
, but more sophisticated methods are now used. These are the most common methods now used for that purpose: *to fit a mathematical formula, such as an extension of the Gompertz function, to the data. *for relatively small amounts of data, to look at an established
mortality table In actuarial science and demography, a life table (also called a mortality table or actuarial table) is a table which shows, for each age, what the probability is that a person of that age will die before their next birthday ("probability of death" ...
that was previously derived for a larger population and make a simple adjustment to it (as multiply by a constant factor) to fit the data. *with a large number of data points, one looks at the mortality rates actually experienced at each age and applies to smooth (as by
cubic splines Image:Parametic Cubic Spline.svg, Single knots at 1/3 and 2/3 establish a spline of three cubic polynomials meeting with ''C''2 continuity. Triple knots at both ends of the interval ensure that the curve interpolates the end points In mathematics, ...
). While the data required are easily identified in the case of humans, the computation of life expectancy of industrial products and wild animals involves more indirect techniques. The life expectancy and demography of wild animals are often estimated by capturing, marking, and recapturing them. The life of a product, more often termed
shelf life Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or just no longer ...
, is also computed using similar methods. In the case of long-lived components, such as those used in critical applications: in aircraft, methods like
accelerated aging Accelerated aging is testing that uses aggravated conditions of heat, humidity, oxygen, sunlight, vibration, etc. to speed up the normal aging processes of items. It is used to help determine the long-term effects of expected levels of stress withi ...
are used to model the life expectancy of a component.Eliahu Zahavi, Vladimir Torbilo & Solomon Press (1996) Fatigue Design: Life Expectancy of Machine Parts. CRC Press. . The age-specific death rates are calculated separately for separate groups of data that are believed to have different mortality rates (such as males and females, and perhaps smokers and non-smokers if data are available separately for those groups) and are then used to calculate a
life table In actuarial science Actuarial science is the discipline that applies mathematical Mathematics (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic ...
from which one can calculate the probability of surviving to each age. In
actuarial notation Actuarial notation is a shorthand method to allow Actuary, actuaries to record mathematical formulas that deal with Interest, interest rates and life tables. Traditional notation uses a halo system where symbols are placed as superscript or subscr ...

actuarial notation
, the probability of surviving from age x to age x+n is denoted \,_np_x\! and the probability of dying during age x (between ages x and x+1) is denoted q_x\!. For example, if 10% of a group of people alive at their 90th birthday die before their 91st birthday, the age-specific death probability at 90 would be 10%. That is a probability, not a mortality rate. The expected future lifetime of a life age x in whole years (the ''curtate expected lifetime'' of ''(x)'') is denoted by the symbol \,e_x\!. It is the conditional expected future lifetime (in whole years), assuming survival to age x. If K(x) denotes the curtate future lifetime at x, :e_x = \operatorname (x)= \sum_^\infty k\, \Pr(K(x)=k) = \sum_^k\, \,_kp_x \,\, q_. Substituting _kp_x \, q_ = _k p_x - _p_x in the sum and simplifying gives the equivalent formula:e_x = \sum_^\infty \, _k p_x. If the assumption is made that on average, people live a half year in the year of death, the complete expectation of future lifetime at age x is e_x + 1/2. Life expectancy is by definition an
arithmetic mean In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities and t ...
. It can also be calculated by integrating the survival curve from 0 to positive infinity (or equivalently to the maximum lifespan, sometimes called 'omega'). For an extinct or completed
cohort Cohort or cohortes may refer to: * Cohort (educational group), a group of students working together through the same academic curriculum * Cohort (floating point), a set of different encodings of the same numerical value * Cohort (military unit), ...
(all people born in the year 1850, for example), it can of course simply be calculated by averaging the ages at death. For cohorts with some survivors, it is estimated by using mortality experience in recent years. The estimates are called period cohort life expectancies. It is important to note that the statistic is usually based on past mortality experience and assumes that the same age-specific mortality rates will continue. Thus, such life expectancy figures need to be adjusted for temporal trends before calculating how long a currently living individual of a particular age is expected to live. Period life expectancy remains a commonly used statistic to summarize the current health status of a population. However, for some purposes, such as pensions calculations, it is usual to adjust the life table used by assuming that age-specific death rates will continue to decrease over the years, as they have usually done in the past. That is often done by simply extrapolating past trends, but some models exist to account for the evolution of mortality like the Lee–Carter model. As discussed above, on an individual basis, some factors correlate with longer life. Factors that are associated with variations in life expectancy include family history, marital status, economic status, physique, exercise, diet, drug use including smoking and alcohol consumption, disposition, education, environment, sleep, climate, and health care.


Healthy life expectancy

To assess the quality of these additional years of life, 'healthy life expectancy' has been calculated for the last 30 years. Since 2001, the World Health Organization has published statistics called Healthy life expectancy (HALE), defined as the average number of years that a person can expect to live in "full health" excluding the years lived in less than full health due to disease and/or injury. Since 2004,
Eurostat Eurostat (European Statistical Office) is a Directorate-General Within the European Union, directorates-general are departments of the European Union government with specific zones of responsibility, the equivalent of Ministry (government depar ...

Eurostat
publishes annual statistics called
Healthy Life Years The Healthy Life Years indicator (HLY), also known as disability-free life expectancy Life expectancy is a statistical measure of the average (see below) time an organism is expected to live, based on the year of its birth, its current age, a ...
(HLY) based on reported activity limitations. The
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

United States
uses similar indicators in the framework of the national health promotion and disease prevention plan " Healthy People 2010". More and more countries are using health expectancy indicators to monitor the health of their population. The long-standing quest for longer life led in the 2010s to a more promising focus on increasing HALE, also known as a person's "healthspan". Besides the benefits of keeping people healthier longer, a goal is to reduce health-care expenses on the many diseases associated with
cellular senescence File:SABG MEFs.jpg, (Upper) Primary mouse embryonic fibroblast cells (MEFs) before senescence. Spindle-shaped.(Lower) MEFs became senescent after passages. Cells grow larger, flatten shape and expressed senescence-associated Beta-galactosidase, β- ...

cellular senescence
. Approaches being explored include
fasting Fasting is the willful refrainment from eating Eating (also known as consuming) is the ingestion Ingestion is the consumption of a substance by an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ...

fasting
,
exercise Exercise is any bodily activity that enhances or maintains physical fitness Physical fitness is a state of health Health is a state of physical, mental and social well-being Well-being, also known as ''wellness'', ''prudential value ...

exercise
, and
senolytic A senolytic (from the words ''senescence Ann Pouder American supercentenarians are citizens or residents of the United States who have attained or surpassed 110 years of age. , the Gerontology Research Group The Gerontology Research Group ( ...
drugs.


Forecasting

Forecasting life expectancy and mortality form an important subdivision of
demography Demography (from prefix ''demo-'' from Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period ...

demography
. Future trends in life expectancy have huge implications for old-age support programs like U.S. Social Security and
pension A pension (, from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be ...

pension
since the cash flow in these systems depends on the number of recipients who are still living (along with the rate of return on the investments or the tax rate in
pay-as-you-go Pay as you go or PAYG may refer to: Finance * Pay-as-you-go tax or pay-as-you-earn tax * PAYGO, the practice in the US of financing expenditures with current funds rather than borrowing * PAUG, a structured financial product * Prepayment (disambigu ...
systems). With longer life expectancies, the systems see increased cash outflow; if the systems underestimate increases in life-expectancies, they will be unprepared for the large payments that will occur, as humans live longer and longer. Life expectancy forecasting is usually based on two different approaches: *Forecasting the life expectancy directly, generally using
ARIMA Arima, officially The Royal Chartered Borough of Arima is the easternmost and second largest in area of the three boroughs of Trinidad and Tobago Trinidad and Tobago (, ), officially the Republic of Trinidad and Tobago, is the southern ...
or other time-series extrapolation procedures: that has the advantage of simplicity, but it cannot account for changes in mortality at specific ages, and the forecast number cannot be used to derive other
life table In actuarial science Actuarial science is the discipline that applies mathematical Mathematics (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic ...
results. Analyses and forecasts using this approach can be done with any common statistical/mathematical software package, like
EViews EViews is a statistical package Statistical software are specialized computer programs for analysis in statistics and econometrics. Open-source * ADaMSoft – a generalized statistical software with data mining algorithms and methods for data ...
, R, SAS,
Stata Stata (, , alternatively , occasionally stylized as STATA) is a general-purpose statistical Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying stati ...

Stata
,
Matlab MATLAB (an abbreviation of "MATrix LABoratory") is a and environment developed by . MATLAB allows manipulations, plotting of and data, implementation of s, creation of s, and interfacing with programs written in other languages. Althoug ...
, or
SPSS SPSS Statistics is a statistical software Statistical software are specialized computer program A computer program is a collection of instructions that can be executed by a computer to perform a specific task. A computer program is usual ...

SPSS
. *Forecasting age-specific
death rates Mortality rate, or death rate, is a measure of the number of death (1906) Death is the permanent, Irreversible process, irreversible cessation of all biological process, biological functions that sustain a living organism. Brain death is ...
and computing the life expectancy from the results with life table methods: that is usually more complex than simply forecasting life expectancy because the analyst must deal with correlated age-specific mortality rates, but it seems to be more robust than simple one-dimensional time series approaches. It also yields a set of age specific-rates that may be used to derive other measures, such as survival curves or life expectancies at different ages. The most important approach within this group is the Lee-Carter model, which uses the
singular value decomposition In linear algebra, the singular value decomposition (SVD) is a Matrix decomposition, factorization of a real number, real or complex number, complex matrix (mathematics), matrix. It generalizes the eigendecomposition of a square normal matrix w ...

singular value decomposition
on a set of transformed age-specific mortality rates to reduce their dimensionality to a single time series, forecasts that time series and then recovers a full set of age-specific mortality rates from that forecasted value. The software includes Professor Rob J. Hyndman'
R package called `demography`
an
UC Berkeley's LCFIT system


Policy uses

Life expectancy is one of the factors in measuring the
Human Development Index The Human Development Index (HDI) is a statistic composite index of life expectancy Life expectancy is a statistical measure of the average time an organism is expected to live, based on the year of its birth, its current age, and ot ...
(HDI) of each nation along with adult literacy, education, and standard of living. Life expectancy is also used in describing the physical quality of life of an area or, for an individual when the value of a life settlement is determined a life insurance policy is sold for a cash asset. Disparities in life expectancy are often cited as demonstrating the need for better medical care or increased social support. A strongly associated indirect measure is
income inequality There are wide varieties of economic inequality, most notably measured using the distribution of incomeIn economics Economics () is the social science that studies how people interact with value; in particular, the Production (econom ...
. For the top 21 industrialized countries, if each person is counted equally, life expectancy is lower in more unequal countries (r = −0.907). There is a similar relationship among states in the US (r = −0.620).


Life expectancy vs. maximum life span

Life expectancy is commonly confused with the average age an adult could expect to live. This confusion may create the expectation that an adult would be unlikely to exceed an average life expectancy, even though, with all statistical probability, an adult, who has already avoided many statistical causes of adolescent mortality, should be expected to outlive the average life expectancy calculated from birth. One must compare the life expectancy of the period after childhood, to estimate the life expectancy of an adult. Life expectancy can change dramatically after childhood, even in preindustrial times as is demonstrated by the Roman Life Expectancy table, which estimates life expectancy to be 25 years ''at birth'', but 53 years upon reaching age 25. Studies like Plymouth Plantation; "Dead at Forty" and Life Expectancy by Age, 1850–2004 similarly show a dramatic increase in life expectancy once adulthood was reached. Life expectancy differs from
maximum life span Maximum life span (or, for humans Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as ...
. Life expectancy is an average for all people in the population — including those who die shortly after birth, those who die in early adulthood (e.g. childbirth, war), and those who live unimpeded until old age. Maximum lifespan is an individual-specific concept — maximum lifespan is, therefore, an upper bound rather than an average. Science author Christopher Wanjek said "has the human race increased its life span? Not at all. This is one of the biggest misconceptions about old age." The maximum life span, or oldest age a human can live, may be constant. Further, there are many examples of people living significantly longer than the average life expectancy of their time period, such as
Socrates Socrates (; ; –399 BC) was a Greek philosopher from Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is the capital city, capital and List of cities in Greece, largest city of Greece. Athens domi ...

Socrates
(71),
Saint Anthony the Great Anthony or Anthony the Great ( grc-gre, Ἀντώνιος ''Antṓnios''; ar, القديس أنطونيوس الكبير; la, Antonius; ; c. 12 January 251 – 17 January 356), was a Christian monk from Egypt, revered since his death as a s ...
(105),
Michelangelo Michelangelo di Lodovico Buonarroti Simoni (; 6 March 1475 – 18 February 1564), known simply as Michelangelo (), was an Italian sculptor, painter, architect and poet of the High Renaissance In art history, the High Renaissance was ...

Michelangelo
(88), and
John Adams John Adams (October 30, 1735 – July 4, 1826) was an American statesman, attorney, diplomat A diplomat (from grc, δίπλωμα; romanized Romanization or romanisation, in linguistics Linguistics is the scientific study of ...

John Adams
, 2nd president of the United States (90). However, anthropologist John D. Hawks criticizes the popular conflation of life span (life expectancy) and
maximum life span Maximum life span (or, for humans Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as ...
when popular science writers falsely imply that the average adult human does not live longer than their ancestors. He writes, " e-specific mortality rates have declined across the adult lifespan. A smaller fraction of adults die at 20, at 30, at 40, at 50, and so on across the lifespan. As a result, we live longer on average... In every way we can measure, human lifespans are longer today than in the immediate past, and longer today than they were 2000 years ago... age-specific mortality rates in adults really have reduced substantially."


See also


Increasing life expectancy


Notes

a. In standard actuarial notation, ''e'' refers to the expected future lifetime of ''(x)'' in whole years, while ''eͦ'' (with a ring above the ''e'') denotes the complete expected future lifetime of ''(x)'', including the fraction.


References


Further reading

*
Leonid A. Gavrilov The reliability theory of aging is an attempt to apply the principles of reliability theory Reliability engineering is a sub-discipline of systems engineering Systems engineering is an interdisciplinary field of engineering and engineering ...
& Natalia S. Gavrilova (1991), ''The Biology of Life Span: A Quantitative Approach''. New York: Harwood Academic Publisher, *Kochanek, Kenneth D., Elizabeth Arias, and Robert N. Anderson (2013),
How Did Cause of Death Contribute to Racial Differences in Life Expectancy in the United States in 2010?
'. Hyattsville, Md.:
U.S. Department of Health and Human Services The United States Department of Health and Human Services (HHS), also known as the Health Department, is a cabinet-level executive branch The executive is the branch of government exercising authority in and holding Moral responsibility, r ...
,
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services The United States Department of Heal ...
,
National Center for Health Statistics The National Center for Health Statistics (NCHS) is a principal agency of the U.S. Federal Statistical System, which provides statistical information to guide actions and policies to improve the public health Public health has been defined a ...
.


External links


Charts for all countriesOur World In Data – Life Expectancy
Visualizations of how life expectancy around the world has changed historically (by
Max Roser Max Roser (born 1983) is an economist An economist is a professional and practitioner in the social science Social science is the Branches of science, branch of science devoted to the study of society, societies and the Social relation, ...
). Includes life expectancy for different age groups. Charts for all countries, world maps, and links to more data sources.
Global Agewatch has the latest internationally comparable statistics on life expectancy from 195 countries.
from the CIA's World Factbook.

from the US Centers for Disease Controls and Prevention, National Center for Health Statistics.

from the University of Texas. *Animal lifespans

from Tesarta Online (Internet Archive)

from Dr. Bob's All Creatures Site. {{DEFAULTSORT:Life Expectancy Actuarial science Demographic economics Senescence Demography Population