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. In the early phase of anthropometric research history, questions about height measuring 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. There are many pathological processes, both inherited and acquired, but the heights of many exceptional (>2 standard deviations from the mean) individuals are considered as natural variants. When no cause can be identified the deviation may be benign or pathological, and is considered idiopathic tall or short stature. When inheritance is concluded as the cause, as a natural variant, of exceptional height the term is familial tall or short stature. A variant related to familial stature, and sometimes used synonymously, and in some cases to distinguish height of a juvenile that is at a particular age significantly above or below average but is ultimately expected to become near average adult height is constitutional tall or short stature. 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.
Determinants of growth
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. Outside the womb, humans grow fastest 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 rate decays 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, although there is limited research to suggest minor height growth after the age of 19 in males. 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 behavioral development, again suggesting an ultimate cause of resources and family status rather than a purely biological explanation. In 1988, it was observed that first-born males were shorter than later-born males. However, in 2013, the reverse observation was made. The study authors suggest that the cause may be socioeconomic in nature.
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