Tall men and women are more likely to suffer a potentially deadly blood clot, warns new research.
A study of more than two million siblings found a direct link between height and venous thromboembolism - a serious condition where a clot forms in a vein.
Men 6ft 2in or taller were 65 per cent more at risk than those shorter than 5ft 3in.
Women pregnant for the first time who were at least 6ft were 69 per cent more at risk than those shorter than 5ft 1in.
Pregnancy makes women’s blood more likely to clot to protect against heavy bleeding when they give birth.
Lead researcher Professor Bengt Zoller, of Lund University in Sweden, said: “Height is not something we can do anything about.
“However, the height in the population has increased, and continues increasing, which could be contributing to the fact that the incidence of thrombosis has increased.”
Each year about 25,000 people in the UK die from venous thromboembolism and about one in 500 Britons will get it.
It starts in a vein and includes two types of blood clots - deep vein thrombosis (DVT) which forms in the leg and pulmonary embolism (PE) which happens when the clot breaks free and travels to the lung.
Both can be fatal but can be treated with injectable drugs that dissolve the clots or blood thinning medications that combat them. Removal by surgery is another option.
Previous research has suggested the risk of venous thromboembolism among men 6ft or over is more than two-and-a-half-times greater.
The study, published in the journal Circulation: Cardiovascular Genetics, involved participants from Sweden where the population is now as ethnically diverse as the US, said Prof Zoller.
He said the shorter they were the less the likelihood of them developing the blood clot.
Each year thousands of Britons develop the serious, potentially fatal, medical condition.
The most common triggers are surgery, cancer, immobilisation and hospitalisation.
Hormones ‘a major cause’
In women pregnancy and use of hormones like the Pill or oestrogen for menopause symptoms are also major causes.
Prof Zoller said gravity could be behind the association between height and venous thromboembolism risk.
He said: “It could just be that because taller individuals have longer leg veins there is more surface area where problems can occur.
“There is also more gravitational pressure in leg veins of taller persons that can increase the risk of blood flow slowing or temporarily stopping.”
One theory is blood must be pumped a longer distance in tall people which may cause reduced flow in the legs and thereby raise the risk of clotting.
Another possible connection is that taller people tend to weigh more - and increased weight, particularly in those who are obese, puts extra pressure on the legs and calves, and so reduces blood flow.
Prof Zoller said: “I think we should start to include height in risk assessment just as overweight, although formal studies are needed to determine exactly how height interacts with inherited blood disorders and other conditions.”
Being short has also been found to carry a reduced risk of cancer - possibly because they have a larger number of cells in their body which could potentially lead to a tumour.
The vertically challenged are also more likely to live longer because the hormone that controls height - called the Insulin-like Growth Factor (IGF) - also controls ageing. A low level of IGF means a longer life expectancy.
It’s estimated venous thromboembolism affects up to 600,000 Americans every year - making it the third leading cause of heart attack and stroke.