Ask the doctors: Study finds tall people more likely to develop blood clots

Dear Doctor: Our uncle, who is 44, recently got diagnosed with a blood clot in his leg, and it was a medical emergency. Our mom (she’s his older sister) is a nurse and says that because he’s so tall – 6-foot-4 – his risk is higher. Is that really true? I thought that it depended more on weight than height.

Dear Reader: Kudos to your mother, who is up on the latest research. According to a study published last year in the American Heart Association’s journal Circulation: Cardiovascular Genetics, scientists in Sweden have identified a potential relationship between someone’s height and their risk of developing a blood clot.

In the study, men under 5 feet 3 inches were found to be 65 percent less likely than men taller than 6 feet 2 inches to develop a venous blood clot. In women, the likelihood of a blood clot was 69 percent lower in individuals shorter than 5 feet 1 inch than in those who were 6 feet or taller. For the taller men in the study, height was linked to blood clots in the lungs, legs and other locations. For women, being tall increased the risk of blood clots only in the legs.

These conclusions are drawn from an analysis of medical data collected from – and this is an interesting twist – more than 2.5 million adult siblings in a national registry. The study period ranged from 30 to 40 years, and siblings were used to help account for any potential genetic factors in the results. None of the subjects had venous blood clots at the start of the study period.

The ability of blood to clot, or coagulate, is crucial to our survival. When an injury occurs, factors present in our blood and plasma work together to form the clot, which slows or stops the flow of blood at the site. As the injury heals, the clot dissolves. However, blood clots can form within blood vessels absent of injury or trauma, and they can persist. The danger is that they can restrict blood flow.

Blood clots can also separate from their point of origin and travel through the heart and to lungs, where they become life-threatening. According to statistics from the Centers for Disease Control and Prevention, between 60,000 and 100,000 deaths per year are attributable to blood clots.

You’re correct that being overweight or obese is a risk factor in developing a blood clot. So are smoking, pregnancy, being immobile for long stretches of time, having high blood pressure or high cholesterol, and family history, to name just a few. Although you can’t stop being tall, you can take steps to reduce blood-clot risk.

The first three – lose weight, exercise regularly and stop smoking – not only lower blood clot risk, they contribute to health and well-being in general. Air travel, desk work, bed rest and medical recovery can mean sitting still for hours at a time. Mitigate this by walking, stretching and flexing your leg muscles at regular intervals. And if you do find yourself seated for a long while, avoid crossing your legs, which can impede blood flow.