Human height or stature is the distance from the bottom of the feet to the top of the head in a human body, standing erect. It is measured using a stadiometer, usually in centimetres when using the metric system, or feet and inches when using the imperial system.
A particular genetic profile in men called Y haplotype I-M170 is correlated with height. Ecological data shows that as the frequency of this genetic profile increases in the population, the average male height in a country also increases.
When populations share genetic background and environmental factors, average height is frequently characteristic within the group. Exceptional height variation (around 20% deviation from average) within such a population is sometimes due to gigantism or dwarfism, which are medical conditions caused by specific genes or endocrine abnormalities.
The development of human height can serve as an indicator of two key welfare components, namely nutritional quality and health. In regions of poverty or warfare, environmental factors like chronic malnutrition during childhood or adolescence may result in delayed growth and/or marked reductions in adult stature even without the presence of any of these medical conditions.
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Determinants of growth and height
The study of height is known as auxology. Growth has long been recognized as a measure of the health of individuals, hence part of the reasoning for the use of growth charts. For individuals, as indicators of health problems, growth trends are tracked for significant deviations and growth is also monitored for significant deficiency from genetic expectations. Genetics is a major factor in determining the height of individuals, though it is far less influential in regard to differences among populations. Average height is relevant to the measurement of the health and wellness (standard of living and quality of life) of populations.
Attributed as a significant reason for the trend of increasing height in parts of Europe are the egalitarian populations where proper medical care and adequate nutrition are relatively equally distributed. Average (male) height in a nation is correlated with protein quality. Nations that consume more protein in the form of pork, dairy, eggs, and fish tend to be taller, while those that attain more protein from cereals tend to be shorter.
Changes in diet (nutrition) and a general rise in quality of health care and standard of living are the cited factors in the Asian populations. Malnutrition including chronic undernutrition and acute malnutrition is known to have caused stunted growth in various populations. This has been seen in North Korea, parts of Africa, certain historical Europe, and other populations. Developing countries such as Guatemala have rates of stunting in children under 5 living as high as 82.2% in Totonicapán, and 49.8% nationwide.
Height measurements are by nature subject to statistical sampling errors even for a single individual. In a clinical situation, height measurements are seldom taken more often than once per office visit, which may mean sampling taking place a week to several months apart. The smooth 50th percentile male and female growth curves illustrated above are aggregate values from thousands of individuals sampled at ages from birth to age 20. In reality, a single individual's growth curve shows large upward and downward spikes, partly due to actual differences in growth velocity, and partly due to small measurement errors.
For example, a typical measurement error of plus or minus 0.5 cm may completely nullify 0.5 cm of actual growth resulting in either a "negative" 0.5 cm growth (due to overestimation in the previous visit combined with underestimation in the latter), up to a 1.5 cm growth (the first visit underestimating and the second visit overestimating) in the same elapsed time period between measurements. Note there is a discontinuity in the growth curves at age 2, which reflects the difference in recumbent length (with the child on his or her back), used in measuring infants and toddlers and standing height typically measured from age 2 onwards.
Height, like other phenotypic traits, is determined by a combination of genetics and environmental factors. A child's height based on parental heights is subject to regression toward the mean, therefore extremely tall or short parents will likely have correspondingly taller or shorter offspring, but their offspring will also likely be closer to average height than the parents themselves. Genetic potential and a number of hormones, minus illness, is a basic determinant for height. Other factors include the genetic response to external factors such as diet, exercise, environment, and life circumstances.
Humans grow fastest (other than in the womb) as infants and toddlers, rapidly declining from a maximum at birth to roughly age 2, tapering to a slowly declining rate, and then during the pubertal growth spurt, a rapid rise to a second maximum (at around 11-12 years for female, and 13-14 years for male), followed by a steady decline to zero. On average, female growth speed trails off to zero at about 15 or 16 years, whereas the male curve continues for approximately 3 more years, going to zero at about 18-20. These are also critical periods where stressors such as malnutrition (or even severe child neglect) have the greatest effect.
Moreover, the health of a mother throughout her life, especially during her critical period and pregnancy, has a role. A healthier child and adult develops a body that is better able to provide optimal prenatal conditions. The pregnant mother's health is important for herself but also for the fetus as gestation is itself a critical period for an embryo/fetus, though some problems affecting height during this period are resolved by catch-up growth assuming childhood conditions are good. Thus, there is a cumulative generation effect such that nutrition and health over generations influences the height of descendants to varying degrees.
The age of the mother also has some influence on her child's height. Studies in modern times have observed a gradual increase in height with maternal age, though these early studies suggest that trend is due to various socio-economic situations that select certain demographics as being more likely to have a first birth early in the mother's life. These same studies show that children born to a young mother are more likely to have below-average educational and behavioural development, again suggesting an ultimate cause of resources and family status rather than a purely biological explanation.
It has been observed that first-born males are shorter than later-born males. However, more recently the reverse observation was made. The study authors suggest that the cause may be socio-economic in nature.
Nature versus nurture
The precise relationship between genetics and environment is complex and uncertain. Differences in human height is 60-80% heritable, according to several twin studies and has been considered polygenic since the Mendelian-biometrician debate a hundred years ago. A genome-wide association (GWA) study of more than 180,000 individuals has identified hundreds of genetic variants in at least 180 loci associated with adult human height. The number of individuals has since been expanded to 253,288 individuals and the number of genetic variants identified is 697 in 423 genetic loci. In a separate study of body proportion using sitting-height ratio, it reports that these 697 variants can be partitioned into 3 specific classes, (1) variants that primarily determine leg length, (2) variants that primarily determine spine and head length, or (3) variants that affect overall body size. This gives insights into the biological mechanisms underlying how these 697 genetic variants affect overall height. These loci do not only determine height, but other features or characteristics. As an example, 4 of the 7 loci identified for intracranial volume had previously been discovered for human height.
The effect of environment on height is illustrated by studies performed by anthropologist Barry Bogin and coworkers of Guatemala Mayan children living in the United States. In the early 1970s, when Bogin first visited Guatemala, he observed that Mayan Indian men averaged only 157.5 centimetres (5 ft 2 in) in height and the women averaged 142.2 centimetres (4 ft 8 in). Bogin took another series of measurements after the Guatemalan Civil War, during which up to a million Guatemalans fled to the United States. He discovered that Maya refugees, who ranged from six to twelve years old, were significantly taller than their Guatemalan counterparts. By 2000, the American Maya were 10.24 cm (4.03 in) taller than the Guatemalan Maya of the same age, largely due to better nutrition and health care. Bogin also noted that American Maya children had relatively longer legs, averaging 7.02 cm (2.76 in) longer than the Guatemalan Maya (a significantly lower sitting height ratio).
The Nilotic peoples of Sudan such as the Shilluk and Dinka have been described as some of the tallest in the world. Dinka Ruweng males investigated by Roberts in 1953-54 were on average 181.3 centimetres (5 ft 11 1/2 in) tall, and Shilluk males averaged 182.6 centimetres (6 ft 0 in). The Nilotic people are characterized as having long legs, narrow bodies and short trunks, an adaptation to hot weather. However, male Dinka and Shilluk refugees measured in 1995 in Southwestern Ethiopia were on average only 176.4 cm and 172.6 cm tall, respectively. As the study points out, Nilotic people "may attain greater height if privileged with favourable environmental conditions during early childhood and adolescence, allowing full expression of the genetic material." Before fleeing, these refugees were subject to privation as a consequence of the succession of civil wars in their country from 1955 to the present.
The tallest living married couple are ex-basketball players Yao Ming and Ye Li (both of China) who measure 228.6 cm (7 ft 6 in) and 190.5 cm (6 ft 3 in) respectively, giving a combined height of 419.1 cm (13 ft 9 in). They married in Shanghai, China, on 6 August 2007.
In Tibet, the khampas are known for their great height. Khampa males are on average 180 cm tall (5 ft 11 in).
The people of the Dinaric Alps mainly South Slavs (Montenegro and East Herzegovina) are on record as being the tallest in the world, with a male average height of 185.6 cm (6 ft 1.1 in) and female average height of 170.9 cm (5 ft 7.3 in).
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Process of growth
Growth in stature, determined by its various factors, results from the lengthening of bones via cellular divisions chiefly regulated by somatotropin (human growth hormone (hGH)) secreted by the anterior pituitary gland. Somatotropin also stimulates the release of another growth inducing hormone Insulin-like growth factor 1 (IGF-1) mainly by the liver. Both hormones operate on most tissues of the body, have many other functions, and continue to be secreted throughout life; with peak levels coinciding with peak growth velocity, and gradually subsiding with age after adolescence. The bulk of secretion occurs in bursts (especially for adolescents) with the largest during sleep.
The majority of linear growth occurs as growth of cartilage at the epiphysis (ends) of the long bones which gradually ossify to form hard bone. The legs compose approximately half of adult human height, and leg length is a somewhat sexually dimorphic trait, with men having proportionately longer legs. Some of this growth occurs after the growth spurt of the long bones has ceased or slowed. The majority of growth during growth spurts is of the long bones. Additionally, the variation in height between populations and across time is largely due to changes in leg length. The remainder of height consists of the cranium. Height is sexually dimorphic and statistically it is more or less normally distributed, but with heavy tails. It has been shown that a log-normal distribution fits the data equally well, besides guaranteeing a non-negative lower confidence limit, which could otherwise attain a non-physical negative height value for arbitrarily large confidence levels.
Height abnormalities
Most intra-population variance of height is genetic. Short stature and tall stature are usually not a health concern. If the degree of deviation from normal is significant, hereditary short stature is known as familial short stature and tall stature is known as familial tall stature. Confirmation that exceptional height is normal for a respective person can be ascertained from comparing stature of family members and analyzing growth trends for abrupt changes, among others. There are, however, various diseases and disorders that cause growth abnormalities.
Most notably, extreme height may be pathological, such as gigantism resulting from childhood hyperpituitarism, and dwarfism which has various causes. Rarely, no cause can be found for extreme height; very short persons may be termed as having idiopathic short stature. The United States Food and Drug Administration (FDA) in 2003 approved hGH treatment for those 2.25 standard deviations below the population mean (approximately the lowest 1.2% of the population). An even rarer occurrence, or at least less used term and recognized "problem", is idiopathic tall stature.
If not enough growth hormone is produced and/or secreted by the pituitary gland, then a patient with growth hormone deficiency can undergo treatment. This treatment involves the injection of pure growth hormone into thick tissue to promote growth.
Role of an individual's height
Height and health
Certain studies have shown that height is a factor in overall health while some suggest tallness is associated with better cardiovascular health and shortness with longevity. Cancer risk has also been found to grow with height.
Nonetheless, modern westernized interpretations of the relationship between height and health fail to account for the observed height variations worldwide. Cavalli-Sforza and Cavalli-Sforza note that variations in height worldwide can be partly attributed to evolutionary pressures resulting from differing environments. These evolutionary pressures result in height related health implications. While tallness is an adaptive benefit in colder climates such as found in Europe, shortness helps dissipate body heat in warmer climatic regions. Consequently, the relationships between health and height cannot be easily generalized since tallness and shortness can both provide health benefits in different environmental settings.
At the extreme end, being excessively tall can cause various medical problems, including cardiovascular problems, because of the increased load on the heart to supply the body with blood, and problems resulting from the increased time it takes the brain to communicate with the extremities. For example, Robert Wadlow, the tallest man known to verifiable history, developed trouble walking as his height increased throughout his life. In many of the pictures of the later portion of his life, Wadlow can be seen gripping something for support. Late in his life, although he died at age 22, he had to wear braces on his legs and walk with a cane; and he died after developing an infection in his legs because he was unable to feel the irritation and cutting caused by his leg braces.
Sources are in disagreement about the overall relationship between height and longevity. Samaras and Elrick, in the Western Journal of Medicine, demonstrate an inverse correlation between height and longevity in several mammals including humans.
Women whose height is under 150 cm (4 ft 11 in) may have a small pelvis, resulting in such complications during childbirth as shoulder dystocia.
A study done in Sweden in 2005 has shown that there is a strong inverse correlation between height and suicide among Swedish men.
A large body of human and animal evidence indicates that shorter, smaller bodies age slower, and have fewer chronic diseases and greater longevity. For example, a study found eight areas of support for the "smaller lives longer" thesis. These areas of evidence include studies involving longevity, life expectancy, centenarians, male vs. female longevity differences, mortality advantages of shorter people, survival findings, smaller body size due to calorie restriction, and within species body size differences. They all support the conclusion that smaller individuals live longer in healthy environments and with good nutrition. However, the difference in longevity is modest. Several human studies have found a loss of 0.5 year/centimeter of increased height (1.2 yr/inch). But these findings do not mean that all tall people die young. Many live to advanced ages and some become centenarians.
Height and occupational success
There is a large body of research in psychology, economics, and human biology that has assessed the relationship between several seemingly innocuous physical features (e.g., body height) and occupational success. The correlation between height and success was explored decades ago. Shorter people are considered to have an advantage in certain sports (e.g., gymnastics, race car driving, etc.), whereas in many other sports taller people have a major advantage. In most occupational fields, body height is not relevant to how well people are able to perform, but nonetheless has been found to correlate with their success in several studies, although there may be other factors such as gender or socioeonomic status that explain this.
A demonstration of the height-success association can be found in the realm of politics. In the United States presidential elections, the taller candidate won 22 out of 25 times in the 20th century. Nevertheless, Ignatius Loyola, founder of the Jesuits, was 150 cm (4 ft 11 in) and several prominent world leaders of the 20th century, such as Vladimir Lenin, Benito Mussolini, Nicolae Ceau?escu and Joseph Stalin were of below average height. These examples, however, were all before modern forms of multi-media, i.e., television, which may further height discrimination in modern society. Further, growing evidence suggests that height may be a proxy for confidence, which is likewise strongly correlated with occupational success.
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History of human height
In the 150 years since the mid-19th century, the average human height in industrialised countries has increased by up to 10 centimetres (3.9 in). However, these increases appear to have largely levelled off. Before the mid-19th century there were cycles in height, with periods of increase and decrease; however, examinations of skeletons show no significant differences in height from the Stone Age through the early 1800s.
In the eighteenth and nineteenth centuries, people of European descent in North America were far taller than those in Europe and were the tallest in the world. The original indigenous population of Plains Native Americans was also among the tallest populations of the world at the time.
In the late nineteenth century, the Netherlands was a land renowned for its short population, but today its population is among the world's tallest with young men averaging 183.8 cm (6 ft 0.4 in) tall.
According to a study by economist John Komlos and Francesco Cinnirella, in the first half of the 18th century, the average height of an English male was 165 cm (5 ft 5 in), and the average height of an Irish male was 168 cm (5 ft 6 in). The estimated mean height of English, German, and Scottish soldiers was 163.6 cm - 165.9 cm (5 ft 4.4 in - 5 ft 5.3 in) for the period as a whole, while that of Irish was 167.9 cm (5 ft 6.1 in). The average height of male slaves and convicts in North America was 171 cm (5 ft 7 in).
American-born colonial soldiers of the late 1770s were on average more than 7.6 cm (3 inches) taller than their English counterparts who served in Royal Marines at the same time.
Average height of Americans and Europeans decreased during periods of rapid industrialization, possibly due to rapid population growth and broad decreases in economic status. In early 19th century England, the difference between average height of English upper class youth (students of Sandhurst Military Academy) and English lower class youth (Marine Society boys) reached 22 cm (8.7 in), the highest that has been observed.
Data derived from burials show that before 1850, the mean stature of males and females in Leiden, Netherlands was respectively 166.7 cm (5 ft 5.6 in) and 156.7 cm (5 ft 1.7 in). The average height of 19-year-old Dutch orphans in 1865 was 160 cm (5 ft 3 in).
According to a study by J.W. Drukker and Vincent Tassenaar, the average height of Dutch decreased from 1830 to 1857, even while Dutch real GNP per capita was growing at an average rate of more than 0.5 percent per year. The worst decline were in urban areas that in 1847, the urban height penalty was 2.5 cm (1 in). Urban mortality was also much higher than rural regions. In 1829, the average urban and rural Dutchman was 164 cm (5 ft 4.6 in). By 1856, the average rural Dutchman was 162 cm (5 ft 3.8 in) and urban Dutchman was 158.5 cm (5 ft 2.4 in).
A 2004 report citing a 2003 UNICEF study on the effects of malnutrition in North Korea, due to "successive famines," found young adult males to be significantly shorter. In contrast South Koreans "feasting on an increasingly Western-influenced diet," without famine, were growing taller. The height difference is minimal for Koreans over 40, who grew up at a time when economic conditions in the North were roughly comparable to those in the South, while height disparities are most acute for Koreans who grew up in the mid-1990s - a demographic in which South Koreans are about 12 cm (4.7 in) taller than their North Korean counterparts - as this was a period during which the North was affected by a harsh famine. A study by South Korean anthropologists of North Korean children who had defected to China found that 18-year-old males were 5 inches (13 cm) shorter than South Koreans their age due to malnutrition.
The tallest living man is Sultan Kösen of Turkey, at 251 cm (8 ft 3 in). The tallest man in modern history was Robert Pershing Wadlow (1918-1940), from Illinois, in the United States, who was 272 cm (8 ft 11 in) at the time of his death. The tallest woman in medical history was Zeng Jinlian of Hunan, China, who stood 248 cm (8 ft 1 1/2 in) when she died at the age of 17. The shortest adult human on record was Chandra Bahadur Dangi of Nepal at 54.6 cm (1 ft 9 1/2 in).
Adult height between populations often differs significantly. For example, the average height of women from the Czech Republic is greater than that of men from Malawi. This may be caused by genetic differences, childhood lifestyle differences (nutrition, sleep patterns, physical labor), or both.
Depending on sex, genetic and environmental factors, shrinkage of stature may begin in middle age in some individuals but tends to be universal in the extremely aged. This decrease in height is due to such factors as decreased height of inter-vertebral discs because of desiccation, atrophy of soft tissues and postural changes secondary to degenerative disease.
Average height around the world
As with any statistical data, the accuracy of such data may be questionable for various reasons:
- Some studies may allow subjects to self-report values. Generally speaking, self-reported height tends to be taller than its measured height, although the overestimation of height depends on the reporting subject's height, age, gender and region.
- Test subjects may have been invited instead of chosen at random, resulting in sampling bias.
- Some countries may have significant height gaps between different regions. For instance, one survey shows there is 10.8 cm (4 1/2 in) gap between the tallest state and the shortest state in Germany. Under such circumstances, the mean height may not represent the total population unless sample subjects are appropriately taken from all regions with using weighted average of the different regional groups.
- Different social groups can show different mean height. According to a study in France, executives and professionals are 2.6 cm (1 in) taller, and university students are 2.55 cm (1 in) taller than the national average. As this case shows, data taken from a particular social group may not represent a total population in some countries.
- A relatively small sample of the population may have been measured, which makes it uncertain whether this sample accurately represents the entire population.
- The height of persons can vary over the course of a day, due to factors such as a height increase from exercise done directly before measurement (normally inversely correlated), or a height increase since lying down for a significant period of time (normally inversely correlated). For example, one study revealed a mean decrease of 1.54 centimetres (0.61 in) in the heights of 100 children from getting out of bed in the morning to between 4 and 5 p.m. that same day. Such factors may not have been controlled in some of the studies.
- Men from Bosnia and Herzegovina, the Netherlands, Croatia, Serbia, and Montenegro have the average tallest height. Data suggests that Herzegovinians have the genetic potential to be more than two inches taller than the Dutch. In the Netherlands, about 35% of men have the genetic profile Y haplogroup I-M170, but in Herzegovina, the frequency is over 70%. Extrapolating the genetic trend line suggests that the average Herzegovinian man could possibly be as tall as 190 cm (nearly 6' 3"). Many Herzegovinians do not achieve this potential due to poverty (citizens of Bosnia and Herzegovina were 1.9 cm taller if both of their parents went to university, which is considered as a wealth indicator) and to nutritional choices: religious prohibition on pork may be largely to blame for the shorter average stature of Muslim Herzegovinians.
Source of the article : Wikipedia
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