What determines a person's height?
People of diverse heights populate the world, so why is it that some adults are short, while others are as tall as professional basketball players?
Researchers have found it largely relates to genes. In other words, people with tall parents will likely also need to pay for extra legroom on a flight. But there's another important consideration: Studies have shown that malnourishment or severe disease during childhood can prevent people from reaching their genetic potential for height.
These can affect average changes in height across entire countries. In a 2016 study in the journal eLife, researchers showed that the world's tallest men on average come from the Netherlands, and the world's tallest women on average hail from Latvia. But this league table wasn't always this way, according to the international Non-Communicable Diseases Risk Factor Collaboration (NCD-RisC).
South Korea was 133rd in the 1985 rankings, but by 2019, it had jumped to 60th place. Scientists think this change may be due to improved diets in South Korea in recent decades.
"In South Korea and the People's Republic of China, it's widely understood that increasing height over the last one to two generations is largely due to improved nutrition," Stephen Hsu, a professor of computational mathematics, science and engineering at Michigan State University whose research has looked at predicting a person's height, told Live Science. "Protein and calcium and total calorie intake have all gone up a lot during that time."
Serious diseases can also negatively affect growth, especially if they occur in childhood; celiac disease, anemia and bone diseases such as rickets and juvenile osteoporosis are all examples.
Although an unhealthy diet and serious illness in childhood can lead to a shorter stature, research suggests that genetic coding is far more influential.
In a 2022 study in the journal Nature, researchers looked at the genomes of 5.4 million people — the largest group examined to date to investigate the genetics of height. The team found 12,111 spots in the genome that had a different base, or "letter" of DNA — also known as single nucleotide polymorphism (SNP) — linked with height. Among people with European ancestry, these SNPs accounted for 40% of height variation, while in people of non-European ancestry, they accounted for 10% to 20%.
Most of the SNPs were found in just 20% of the genome in regions associated with skeletal growth disorders, the researchers found. For instance, 25 SNPs were found near the ACAN gene, which is linked with skeletal dysplasia.
And in a 2018 study published in the journal Genetics, Hsu and colleagues used machine learning and computer algorithms to analyze close to half a million genomes of people living in the United Kingdom. After crunching the numbers, the team was able to accurately predict a person's height and bone density from just their genes.
Moreover, genetic mutations and hormonal imbalances have also been linked to short stature, including dwarfism, a condition in which a person stands at 4 feet, 10 inches (147 centimeters) tall or less. There are two subtypes of dwarfism. First, there's what is known as disproportionate dwarfism, which is when some parts of the body are small but others are either of average or above-average size. The other type is proportionate dwarfism, in which all body parts are proportionately smaller than average. Both types of dwarfism are genetic, and there are 200 or so genetic variations that can cause the two forms, according to Stanford at The Tech. Some of these genes are genetically dominant, meaning a person needs to inherit the genes from only one parent, whereas others are genetically recessive, meaning a person needs to inherit the genes from both parents.
RELATED MYSTERIES
—Can carrots give you night vision?
—Why do we bend our arms when we run?
On the opposite end of the spectrum, people can grow to be giants. Take Robert Wadlow, the tallest person in recorded history, who stood 8 feet, 11.1 inches tall (272 cm). Excessive growth like this, sometimes called gigantism, can be a sign of a benign tumor in the pituitary gland, which can overproduce growth hormones.
Barring medical conditions, for well-nourished people, "It appears that genetics largely determines adult height," Hsu said.
Editor's note: Originally published on May 23, 2021 and updated on Jan. 24, 2024 to include information about the 2022 genetics study in the journal Nature.