Life expectancy

This article is about the measure of remaining life. For the Dean Koontz novel, see Life Expectancy (novel).

Life expectancy is the average number of years of life remaining at a given age. It is the average expected lifespan of an individual. Life expectancy is heavily dependent on the criteria used to select the group. In countries with high infant mortality rates, the life expectancy at birth is highly sensitive to the rate of death in the first few years of life. In these cases, another measure such as life expectancy at age 5 (e₅) can be used to exclude the effects of infant mortality to reveal the effects of causes of death other than early childhood causes.

Humans

Variation over time

Humans live on average 31.99 years in Swaziland and on average 81 years in Japan (2008 est.). The oldest confirmed recorded age for any human is 122 years, though some people are reported to have lived longer. This is referred to as the Life span, which is the upper boundary of life, the maximum number of years and individual can live .The following information is derived from the Encyclopaedia Britannica, 1961, as well as other sources and represent estimates of the life expectancies of the population as a whole. In many instances life expectancy varied considerably according to class and gender.

It is important to note that life expectancy rises sharply in all cases for those who reach puberty. A pre 20th Century individual who lived past the teenage years could expect to live to an age close to the life expectancy of today. The ages listed below are an average that includes infant mortalities, but not miscarriage or abortion. This table also rejects certain beliefs based on myths that the ancient humans had life expectancy of hundreds of years. The sharp drop in life expectancy with the advent of the Neolithic mirrors the evidence that the advent of agriculture actually marked a sharp drop in life expectancy that humans are only recovering from in more recent times, mainly in affluent nations.

Humans by Era	Average Lifespan at Birth (years)	Comment
Upper Paleolithic	33	At age 15: 39 (to age 54)
Neolithic	20
Bronze Age	18
Classical Greece	20-30
Classical Rome	20-30
Pre-Columbian North America	25-35
Medieval Islamic Caliphate	35+	The average lifespans of the ruling class were 59–84.3 years in the Middle East and 69–75 in Islamic Spain.
Medieval Britain	20-30
Early 20th Century	30-40
Current world average	66.12 (2008 est.)

During the Industrial Revolution, the life expectancy of children increased dramatically. The percentage of the children born in London who died before the age of five decreased from 74.5% in 1730-1749 to 31.8% in 1810-1829.

Public health measures are credited with much of the recent increase in life expectancy. During 20th century, the average lifespan in the United States increased by more than 30 years; 25 years of which can be attributed to advances in public health.

In order to assess the quality of these additional years of life, health expectancies have been calculated since some thirty years. Since 2001, the World Health Organization is publishing a statistics called Healthy life expectancy (HALE) defined as the average number that a person can expect to live in "full health" by taking into account the years lived in less than full health due to disease and/or injury. Since 2004, Eurostat is yearly publishing a statistics called Healthy Life Years (HLY) based on reported activity limitations. The United States of America use similar indicators in the framework of their nationwide health promotion and disease prevention plan "Healthy People 2010". An increasing number of countries are using health expectancy indicators to monitor the health of their population.

Variation in the world today

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There are great variations in life expectancy worldwide, mostly caused by differences in public health, medical care and diet from country to country. Climate may also have an effect, and the way data is collected may also be an important influence. According to the U.S. Census Bureau, Andorra has the world's longest life expectancy of 83.5 years.

There are also variations between groups within single countries. One example of this is the age expectancy between non-Latino Whites and African Americans in the U.S. Non-Latoino Whites are expected to live until 78 and for African Americans its only 71 . Significant differences still remain in life expectancy between men and women in France and other developed countries, with women outliving men by five years or more. To get some statistics, on average women tend to live until 80 years old whereas men are only expected to live until 74 . These gender differences have been increasing in recent years. Poverty, in particular, has a very substantial effect on life expectancy. In the United Kingdom life expectancy in the wealthiest areas is on average ten years longer than the poorest areas and the gap appears to be increasing as life expectancy for the prosperous continues to increase while in more deprived communities there is little increase. However, in Glasgow the disparity is among the highest in the world with life expectancy for males in the heavily deprived Calton standing at fifty-four — twenty-eight years less than in the affluent area of Lenzie, which is only eight kilometres away.

Life expectancy may also be reduced for people exposed to high levels of highway air pollution or industrial air pollution. Occupation may also have a major effect on life expectancy. Well-educated professionals working in offices have a high life expectancy, while coal miners (and in prior generations, asbestos cutters) do not. Other factors affecting an individual's life expectancy are genetic disorders, obesity, access to health care, diet, exercise, tobacco smoking, and excessive drug and alcohol use.

As pointed out above, AIDS has recently had a negative effect on life expectancy, especially in Sub-Saharan Africa.

Further information: [[:List of countries by life expectancy]]

Sex differences

Women tend to have a lower mortality rate at every age. In the womb, male fetuses have a higher mortality rate (males are conceived at a ratio of about 124 males/100 females, but by birth, the ratio is only 105 males/100 females). Among the smallest premature babies (those under 2 pounds), females have a higher survival rate. At age 110, about 90 percent of the population is female, and this increases still higher to about 92 percent by age 112.

If one does not consider the many women who die while giving birth or in pregnancy, or infanticide, the female human life expectancy is considerably higher than those of men. The reasons for this are not entirely certain. Traditional arguments tend to favor socio-environmental factors: men, on average, consume more tobacco, alcohol and drugs than females in most societies, and are more likely to die from some associated diseases such as lung cancer, tuberculosis and cirrhosis of the liver. Men are more likely to die from injuries, whether unintentional (automotive accidents, etc.), or intentional (suicide, violence, war).. Men are also more likely to die from the leading causes of death (some already stated above) more than women. Some of these in the United States include; cancer of the respiratory system, motor vehicle accidents, suicide, cirrhosis of the liver, emphysema, and coronary heart disease .

However, such arguments are not entirely satisfactory, even if the statistics are corrected for known socio-environmental effects on mortality, females still have longer life expectancy. Interestingly, the age of equalization (about 13) tends to be close to the age of menarche, suggesting a potential reproductive-equilibrium explanation. Women, whose reproductive cycle tends to result in regular blood loss, are better-able to cope with blood loss and trauma.

Some argue that shorter male life expectancy is merely another manifestation of the general rule, seen in all mammal species, that larger individuals tend on average to have shorter lives.. This biological difference occurs because women have more resistance to infections and degenerative diseases .

Lower life expectancy in people with serious mental illness

• 

Persons with serious Mental illness die, on average, 25 years earlier than the general public.

• PDF Morbidity and Mortality in People with Serious Mental Illness
• Serious Mental Illness Suffer From Lack of Integrated Care, Psychiatry News January 5, 2007 Volume 42, Number 1, page 5

Mental illnesses such as schizophrenia, bipolar disorder and major depression. Three out of five mentally ill die from mostly preventable physical diseases. Diseases such as Heart/Cardiovascular disease, Diabetes, Dyslipidaemia, Respiratory ailments, Pneumonia, Influenza.

Centenarians and the Okinawans

The number of centenarians is increasing at a rate of 7 percent per year. For example, in 1980 there were only 15,000 centenarians in the United States. By 2000, that number increased to 77,000. We already know that Japan has the highest life expectancy, which is 81 years old, but they also have the highest ratio in the world of Centenarians. In Okinawa, there are 34.7 centenarians for every 100,000 inhabitants .

The people in Okinawa live so long due to five main things; their diet, low-stress lifestyle, caring community, activeness, and spirituality. The Okinawas diet consists of mainly grains, fish and vegetables. People who eat red meat are proven to have a significantly lower life expectancy. They are very laid back and their community cares for the elders. The fact that the elders are so loved and included in the community might be one of the reasons they live so long. The people of Okinawa stay active both by exercising and keeping a job late in life. The last main thing that increases their life expectancy is the fact that they practice their spirituallity a lot. These are all things we can take away from the Okinawans and try to do them in our own lifes .

Evolution and aging rate

The differing lifespans within various species of plants and animals, including humans, raises the question of why such lifespans are observed.

The evolutionary theory states that organisms that are able by virtue of their defenses or lifestyle to live for long periods whilst avoiding accidents, disease, predation, etc., are likely to have genes that code for slow aging - good repair.

This is so because if a random genetic trait found in the organism increases its survivability, it is more likely to pass on its genes to the next generation. Thus, a member of the population with genes that lend to increased survivability will tend to reproduce more and have more successors. This gene which increases survivability will thus be increasingly spread throughout the species, increasing the survivability of the species as a whole.

Conversely a change to the environment that means that organisms die younger from a common disease or a new threat from a predator will mean that organisms that have genes that code for putting more energy into reproduction than repair will do better.

The support for this theory includes the fact that better defended animals, for example small birds that can fly away from danger live for a decade or more whereas mice which cannot, die of old age in a year or two. Tortoises and turtles are very well defended indeed and can live for over a hundred years. A classic study comparing opossums on a protected island with unprotected opossums also supports this theory.

But there are also counterexamples, suggesting that there is more to the story. Guppies in predator-free habitats evolve shorter life spans than nearby populations of guppies where predators exact a large toll. A broad survey of mammals indicates many more exceptions. The theory of evolution of aging may be in flux.

Another main counterexample is that the evolutionary traits best for short term survival may be detrimental to long term survival. For example, a hummingbird's extremely fast wings allow it to escape from predators and to find mates, assuring that the genetic trait for fast wings is passed on, explained by natural selection. However, these fast wings can be detrimental to the hummingbird's long term health, as the wings consume vast amounts of Adenosine triphosphate (cellular energy molecules) and cause the hummingbird's heart to deteriorate with permanent and long-term wear. This allows for hummingbirds to effectively survive and reproduce; as a result, however, hummingbirds usually die shortly after reproducing.

Natural selection tends to favor short-term survival traits. Human technology driven artificial selection, however, now appears to have prioritized long-term survival traits' having previously improved short-term survival rates through global food-chain dominance.

Calculating life expectancies

The starting point for calculating life expectancies is the age-specific death rates of the population members. For example, if 10% of a group of people alive at their 90th birthday die before their 91st birthday, then the age-specific death rate at age 90 would be 10%.

These values are then used to calculate a life table, from which one can calculate the probability of surviving to each age. In actuarial notation the probability of surviving from age x to age x+n is denoted $\,_{n}p_{x}\!$ and the probability of dying during age x (i.e. between ages x and x+1) is denoted $q_{x}\!$.

The life expectancy at age x, denoted $\,e_{x}\!$, is then calculated by adding up the probabilities to survive to every age. This is the expected number of complete years lived (one may think of it as the number of birthdays they celebrate).

$e_{x}=\sum _{t=1}^{\infty }\,_{t}p_{x}=\sum _{t=0}^{\infty }t\,_{t}p_{x}q_{x+t}$

Because age is rounded down to the last birthday, on average people live half a year beyond their final birthday, so half a year is added to the life expectancy to calculate the full life expectancy.

An average age for death expectancy is very close life expectancy (and exactly same for the exponential growth of death rate with increasing age).

$e_{x}={\frac {\sum _{t=x}^{\infty }\,tq_{t}l_{t}}{\sum _{t=x}^{\infty }\,q_{t}l_{t}}},$

Life expectancy is by definition an arithmetic mean. It can be calculated also by integrating the survival curve from ages 0 to positive infinity (the maximum lifespan, sometimes called 'omega'). For an extinct cohort (all people born in year 1850, for example), of course, it can simply be calculated by averaging the ages at death. For cohorts with some survivors it is estimated by using mortality experience in recent years.

Note that no allowance has been made in this calculation for expected changes in life expectancy in the future. Usually when life expectancy figures are quoted, they have been calculated like this with no allowance for expected future changes. This means that quoted life expectancy figures are not generally appropriate for calculating how long any given individual of a particular age is expected to live, as they effectively assume that current death rates will be "frozen" and not change in the future. Instead, life expectancy figures can be thought of as a useful statistic to summarize the current health status of a population. Some models do exist to account for the evolution of mortality (e.g., the Lee-Carter model).

On an individual basis, there are a number of factors that have been shown to correlate with a longer life. Some factors that influence life expectancy include family history, maritial status, economic status, physique, exercise, diet, alcohol consumption, smoking, disposition, education, environment, sleep, climate, and health care. .

See also

• Biodemography
• Calorie restriction
• Demography
• DNA damage theory of aging
• Economics
• Indefinite lifespan
• Life table
• List of countries by life expectancy
• Maximum life span
• Medieval demography
• Mitohormesis
• Mortality rate
• List of long-living organisms
• Senescence
• Healthcare inequality

Increasing life expectancy

• Strategies for Engineered Negligible Senescence (SENS)
• John Sperling
• Life extension
• Longevity
• Rejuvenation
• Public health
• Infant mortality

References

Further reading

• Leonid A. Gavrilov & Natalia S. Gavrilova (1991), The Biology of Life Span: A Quantitative Approach. New York: Harwood Academic Publisher, ISBN 3-7186-4983-7

External links

• Calculate your life expectancy online (based on the Austrian generation and annuity valuation life tables)
• Rank Order - Life expectancy at birth from the CIA's World Factbook.
• CDC year-by-year life expectancy figures for USA from the USA Centers for Disease Controls and Prevention, National Center for Health Statistics.
• Life expectancy in Roman times from the University of Texas.
• The changing influence of sex and race on life expectancy in the US from Western Washington University.
• Database of life expectancy from multiple countries from The human Mortality Database.
• Animal lifespans: Animal Lifespans from Tesarta Online (Internet Archive); The Life Span of Animals from Dr Bob's All Creatures Site.
• Life expectancy among the countries in the European Union (2007)
• Scientists Have Found the Gene That Decides How Long We Live
• Hans Rosling presents animated data showing global life expectancy from 1820-2020 (video) from TED Conference