human height human height 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, in centimetres when using the metric system or si system, or feet and inches when using united states customary units or the imperial system. human height measurement in the early phase of anthropometric research history, questions about height techniques for measuring nutritional status often concerned genetic differences. height is also important because it is closely correlated with other health components, such as life expectancy. studies show that there is a correlation between small stature and a longer life expectancy. individuals of small stature are also more likely to have lower blood pressure and are less likely to acquire cancer. the university of hawaii has found that the "longevity gene" foxo3 that reduces the effects of aging is more commonly found in individuals of small body size. short stature decreases the risk of venous insufficiency. when populations share genetic backgrounds 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. a study of 20th-century british natality trends indicated that while tall men tended to reproduce more than short men, women of below-average height had more children than taller women. determinants of growth and height the median (50th percentile) growth curves for males and females 0–20 years in the united states. 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 regarding 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. the uneven distribution of nutritional resources makes it more plausible for individuals with better access to resources to grow taller, while individuals with worse access to resources have a lessened chance of growing taller. average height in a nation is correlated with protein quality. nations that consume more protein in the form of meat, dairy, eggs, and fish tend to be taller, while those that obtain more protein from cereals tend to be shorter. therefore, populations with high cattle per capita and high consumption of dairy live longer and are taller. historically, this can be seen in the cases of the united states, argentina, new zealand and australia in the beginning of the 19th century. moreover, when the production and consumption of milk and beef is taken to consideration, it can be seen why the germanic people who lived outside of the roman empire were taller than those who lived at its heart. 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 (0.20 in) 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 (0.6 in) growth (the first visit underestimating and the second visit overestimating) in the same elapsed 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 several 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 (with an average girl starting her puberty and pubertal growth spurt at 10 years and an average boy starting his puberty and pubertal growth spurt at 12 years), a rapid rise to a second maximum (at around 11–12 years for an average female, and 13–14 years for an average male), followed by a steady decline to zero. the average female growth speed trails off to zero at about 15 or 16 years, whereas the average male curve continues for approximately 3 more years, going to zero at about 18–19. 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 essential for herself but also 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 influence 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 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 (5 ft 9+1⁄2 in) and 172.6 cm (5 ft 8 in) 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 (5 ft 11 in). role of an individual's height male stature vs age (us cdc)female stature vs age (us cdc) height and health studies show that there is a correlation between small stature and a longer life expectancy. individuals of small stature are also more likely to have lower blood pressure and are less likely to acquire cancer. the university of hawaii has found that the "longevity gene" foxo3 that reduces the effects of aging is more commonly found in individuals of a small body size. short stature decreases the risk of venous insufficiency. 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. moreover, scientists have also observed a protective effect