Human height varies greatly. People at the extremes of the normal range may be experiencing medical or social problems and should consult a doctor.
Scientists are trying to understand what factors influence a person’s height. A research group called GIANT recently used massive comparisons of genes to find more height-related variants than ever before.
Genetics
Scientists now believe that about 80 percent of one’s height is determined by genetics, with the remaining 20 percent influenced by environmental factors such as nutrition and health. Generally speaking, people who are born tall tend to have children who are also tall, which supports the theory that genes are responsible for the majority of a person’s height. However, the way in which a person grows and the reasons why they grow at different rates can be complicated by other factors, such as hormones and medical conditions.
For example, a woman’s height is influenced not only by her genetic makeup, but also by how much she eats and what kinds of nutrients are in her diet during pregnancy. Those who have healthy, well-balanced diets typically have higher heights than those with poor or unhealthy diets. Consequently, the average global human height continues to rise over time as the world’s standard of living improves and access to nutritious food increases.
In a large study, researchers examined the genomes of 253,288 individuals with European ancestry and found that 424 gene regions and 697 genetic variants are associated with height. The research, published in Nature Genetics, is the largest to date to link individual genes and their function to height. The study’s authors point out that the gene variants discovered so far have small effects, and hundreds, maybe thousands, of additional genes with similar, but smaller, connections to height remain unknown.
The findings of the study were consistent with previous studies and support a model known as “polygenic inheritance,” which posits that multiple (‘poly’) genes, each of which has a relatively small effect on height in itself, and outside environmental influences, contribute to one’s overall height. The analysis also indicated that, for both men and women, heritability varied by geographic-cultural region with the highest heritability in North America and Australia and the lowest in East Asia. In addition, the heritability of height did not show a distinct relation to parental education levels (seen as overlapping CIs). This indicates that differences in educational achievement do not fully explain heritability of human height, and height difference that may be present.
Environment
Human height is partly a genetic trait, but environmental factors play a big role, too. These include nutrition and health, especially during pregnancy, childhood, and adolescence. For example, a child will grow taller if they receive enough nutrients such as proteins, minerals, vitamins A and D, and calcium. Children will also grow taller if they get adequate amounts of sleep and exercise. Other environmental influences include diet, family structure, and lifestyle.
As a rule, people tend to be taller than their parents and other relatives, but genes aren’t the only factor in this. Researchers have found that non-genetic factors outside of the womb contribute to how tall a person will be.
These factors can have a huge impact on a person’s overall health, as well as their risk for diseases like heart disease and diabetes. Researchers have a good understanding of some of these environmental factors, and have used them to develop tools that can predict a person’s risk for disease based on their genetic makeup.
For example, a recent study from the Genetic Investigation of Anthropometric Traits (GIANT) Consortium analyzed the DNA of more than 700,000 adults and discovered 83 new genetic variations that control height. Researchers believe these gene variants can help explain why some people are taller than others, and why certain genetic variants increase a person’s risk for developing common diseases.
Another important environmental factor in human height is the quality of a person’s household environment, which includes nutrition, health care, and employment opportunities. A poorer household environment can lead to more illnesses, which can stunt a child’s growth and cause them to be shorter than their peers. In contrast, a family with a higher socio-economic status is more likely to have healthy children that are of a similar height as their siblings.
One way to look at how the environment affects a person’s height is to compare their average height to that of their ancestors 100 years ago. As the chart shows, the majority of countries saw an increase in both men’s and women’s heights over the century. However, some countries saw more dramatic changes than others. For instance, male and female heights were tallest in Europe and Central Asia, and shortest in North America and Sub-Saharan Africa.
Hormones
People have different amounts of the hormones that control growth. These include growth hormones, which help increase height during childhood; thyroid hormones, which affect a person’s metabolism and sex hormones, which influence the start of puberty and promote bone and muscle development. Hormones also have other effects on the body, including controlling the appetite and regulating blood pressure. People with certain health conditions, such as kidney disease or autoimmune disorders, may have trouble growing to their potential adult height.
For example, the condition acromegaly causes too much of a hormone called growth hormone. This results in a permanent overgrowth of bones, especially those of the hands and feet. The condition also affects the heart and blood vessels, causing high blood pressure and thickening of the skin. Acromegaly is usually caused by a tumour in the pituitary gland, but it can also occur in other parts of the body.
If children have a genetic condition or health issue that stops them growing at their potential height, they can be treated. Treatment for a condition such as growth hormone deficiency, Turner syndrome or a kidney disorder can enable a child to catch up to the height of other children and reach their potential adult height.
However, treatments for sex hormones or growth hormones sold illegally outside pharmacies cannot guarantee an increase in height. In fact, the illegal hormones can cause serious health problems and are on the World Anti-Doping Agency’s Prohibited List.
In addition, sex hormones can have other side effects, such as increasing the risk of heart disease. They can also cause a person to gain weight, which makes them look fatter and less healthy. Some people have difficulty giving up their use of sex hormones because they rely on them to feel good about themselves, but counselling can help. In addition, sleep, exercise and a balanced diet can encourage the natural production of hormones. This means that, for most people, the best way to grow taller is to take care of their body.
Exercise
Most people grow taller if their parents are tall, but genes aren’t the only factor. A variety of medical conditions and hormonal deficiencies can affect height, too. Being too tall can also lead to health problems, such as the extra pressure on the heart and skeleton. Some of the world’s most famously tall individuals, including Robert Wadlow and Sultan Kosen, developed skeletal problems as they grew into adulthood.
Many researchers measure height using crown-rump length, which is the measurement of a fetus or embryo from the top of the head (crown) to the bottom of the buttocks (rump). This measurement is taken when an infant is lying down. The measurement can vary over the course of a day due to changes in blood flow from exercise and because an infant may not always lie down at the same time for long periods of time.
Height measurements can also be affected by the sample size used for a particular study. For example, a study with only executives and professionals might be biased against shorter people because these groups tend to work in more manual labor positions. Also, if the heights of individuals from different regions are not adequately balanced, then the mean results might be skewed.
Humans have seen significant gains in average height over the past century, as illustrated by the relative growth of men and women. The largest average gains have been in Europe and Central Asia, although women around the globe have experienced similar relative increases. Some countries have been more successful in increasing the heights of their population than others.
