People who are tall and obese, especially men, are likely to be at significantly higher risk of developing blood clots in deep veins, according to new research from Tromso in Norway published online this week in Arteriosclerosis, Thrombosis and Vascular Biology: Journal of the American Heart Association.
Blood clots in deep veins are potentially dangerous because they can lead to pulmonary embolism, where a piece of the blood clot breaks off and travels to the blood vessels in the lungs, resulting in heart strain and sometimes sudden death, even at the first occurrence.
A deep vein blood clot that leads to embolism is called venous thromboembolism or VTE.
Research shows that people who are obese are at higher risk for clots in deep veins, usually in the legs. This study shows that being tall as well adds to that risk, particularly in men.
In fact, compared to short, normal-weight men, researchers from the University of Tromsø found that even normal weight tall men had a higher risk of deep vein blood clots, but not as high as being obese and tall.
The advice from the American Heart Association is “if you’re tall, you can reduce your risk by maintaining a healthy weight”.
There was a similar risk pattern for taller women, but this was more difficult to assess, as senior author Dr Sigrid K. Braekkan, a researcher in the Hematological Research Group at the University of Tromsø, explained to the press:
“We believe that we observed the increased risk in tall and normal-weight men, but not women, because most women do not get sufficiently tall.”
“The risk may be present in very tall women, but there were too few to investigate this properly,” said Braekkan.
For the prospective population-based study, which was funded by the University of Tromsø and the Northern Norway Regional Health Authority, Braekkan and colleagues analyzed height and obesity measures of 26,714 men and women aged from 25 to 97 years.
The men and women had taken part in regular health surveys carried out as part of the Tromsø Study, during which, over a median follow up of 12.5 years between 1994 and 2007, there occurred 461 VTEs.
For men, the researchers classed “short” as 5 feet 7.7 inches (1.72 m) or less, and “tall” as 5 feet 11.7 inches (1.82 m) or more.
For women they classed “short” as 5 feet, 2.6 inches (1.59 m) and “tall” as 5 feet 6 inches (1.68 m).
Normal weight was classed as having a Body Mass Index (BMI, weight in kilos divided by square of height in metres) of under 25 kg/m2.
When Braekkan and colleagues analyzed the results they found that:
- Compared with short, normal weight men, the age-adjusted risk of developing VTE was 2.11 times higher in short, obese men; 2.57 times higher in tall, normal weight men; and 5.28 times higher in tall, obese men.
- Compared with short, normal weight women, the age-adjusted risk of developing VTE was 1.83 times higher in short, obese women; not increased at all in tall, normal weight women; and 2.77 times higher in tall, obese women.
The researchers concluded that:
“The combination of obesity and a tall stature was associated with a substantially increased risk of VTE, especially in men, suggesting synergistic effects of obesity and height on risk of VTE in both sexes.”
They commented that the risk posed by being both obese and tall was similar to those conferred by other known risk factors for VTE such as pregnancy, using oral contraceptives, and carrying a gene for Factor V Leiden, an inherited predisposition to blood clotting.
They said more studies should now be done to find out possible biological explanations for the connection between being tall, carrying too much weight, and the risk of VTE.
Braekkan speculated that one such explanation might be that in taller people the pumps in their calf muscles have to pump the blood further, which perhaps reduces blood flow in the legs and this raises the chance of a blood clot compared to shorter people.
It is thought that obesity raises the risk because the excess weight increases the pressure in the abdomen which may also reduce the ability of the pump in the calf muscle to return the blood from the legs.
Plus, as Braekkan explained:
“Obesity is also linked to a state of constant low-grade inflammation, and inflammation may render blood more susceptible to clotting.”
Braekkan and colleagues suggest doctors take both height and weight into account when assessing their patients’ overall risk of dangerous blood clots.
The most important thing, since you can’t change body height, said Braekkan, “is to stay slim, especially if you are tall”.
In previous work the team found a similar pattern of higher risk of blood clot with height in American men, and think these findings are likely to be true of Caucasians populations regardless of where they live.
Estimates from the American Heart Association show that every year, more than 275,000 people in the US are hospitalized with deep vein clots or pulmonary embolisms.
“Joint Effects of Obesity and Body Height on the Risk of Venous Thromboembolism: The Tromsø Study.”
Knut H. Borch, Cecilie Nyegaard, John-Bjarne Hansen, Ellisiv B. Mathiesen, Inger Njølstad, Tom Wilsgaard, and Sigrid K. Brækkan.
Additional source: AHA.
Written by: Catharine Paddock, PhD