Taller people are more likely to develop varicose veins, a condition that causes the blood vessels just under the skin to swell or twist, scientists have found.
Scientists from Stanford University in the US examined the genes of more than 400,000 people in search of clues to what causes this common but little understood condition.
"Genes that predict a person's height may be at the root of this link between height and varicose veins and may provide clues for treating the condition," said Nicholas Leeper, associate professor at Stanford.
The study, published in the journal Circulation, also identified 30 genes linked to varicose vein disorder and to a strong genetic correlation with deep vein thrombosis.
Varicose veins are swollen, twisted veins that can be seen just under the surface of the skin, usually in the legs.
Although the condition is often dismissed as nothing more than a cosmetic nuisance, it can cause moderate pain and has been linked to the more serious side effects of deep vein thrombosis, which occurs when a blood clot forms in one or more of the deep veins in the body.
"The condition is incredibly prevalent but shockingly little is known about the biology. There are no medical therapies that can prevent it or reverse it once it's there," said Alyssa Flores, a medical student at Stanford.
Researchers used data from the UK Biobank -- both a long-term study and genetic repository that includes genomic data on about a half-million people -- to look for varicose vein risk factors using machine learning combined with epidemiological methods in 413,519 participants.
They screened for genetic markers using genomewide association studies in 337,536 of the participants, 9,577 of whom had varicose vein disease.
The study confirmed that currently established risk factors -- including being older, female, overweight or pregnant, or having a history of deep vein thrombosis -- are all associated with varicose veins.
"We confirmed that having had deep vein thrombosis in the past puts you at increased risk in the future," Leeper said.
"Recent research suggests that the converse appears to be true as well. Having varicose veins puts you at risk of these blood clots," he said.
The study also confirmed that surgery on the legs, family history, lack of movement, smoking and hormone therapy are risk factors. However, the correlation they found between height and the condition was unexpected, the researchers said.
"We were very surprised to find that height came up from our machine-learning analyses," Flores said.
"We included 2,716 predictors of varicose veins in this machine-learning algorithm. Then we let the algorithms find the strongest predictors of varicose veins," said Erik Ingelsson, a professor at Stanford.
"Our results strongly suggest height is a cause, not just a correlated factor, but an underlying mechanism leading to varicose veins," Ingelsson said.
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