Being Tall, Obese May Boost Risk of Blood Clots

April 28, 2011 -- Being tall and obese boosts the risk of blood clots, especially in men, according to new research.

Obesity has long been linked with dangerous blood clots in the deep veins, usually in the legs, and with blood clots in the lungs, known as pulmonary embolisms. More recently, experts have found a link with height and cannot thoroughly explain it.

''The present study is the first to investigate the joint effects of obesity and height on the risk of venous clots," says researcher Sigrid Braekkan, PhD, a postdoctoral researcher at the University of Tromso in Norway.

The study is published in Arteriosclerosis, Thrombosis and Vascular Biology: Journal of the American Heart Association.

''The risk is higher in tall, obese men than in tall, obese women," Braekkan tells WebMD in an email interview. "In men, both body height and weight are associated with increased risk of venous clots. In women, body height is not a risk factor alone. However, when combined with obesity, the risk is higher than for obesity alone."

The combination of height and excess weight ''yields a synergistic increase in risk in both men and women," Braekkan says.

Depending on gender, height, and weight, the risk of these blood clots for tall, obese people was up to more than five times higher than for shorter, normal-weight people, Braekkan and colleagues found.

More than 275,000 people a year are hospitalized in the U.S. with deep vein blood clots or lung clots, the American Heart Association estimates.

Risk of Blood Clots: Short vs. Tall, Obese vs. Not

For the study, the researcher evaluated data from the Tromso study in Norway. It includes periodic health surveys of adults, aged 25 to 97, in the Norwegian town of Tromso.

The researchers gathered height and weight information on 26,714 people. They followed them for a median of 12.5 years (half longer, half less).

During the follow-up time, which ended in 2007, 461 blood clots in the deep veins or lungs occurred.

The researchers compared the risk of short, non-obese men to taller and obese men. For the study, short was defined as a man 5 feet, 7.7 inches or shorter. Normal weight is defined as having a body mass index of BMI of under 25. Obesity is having a BMI of 30 or higher.

Compared to the short, normal-weight men:

• Obese, tall men had a 5.28 times higher risk of clots
• Normal-weight and tall men -- with tall defined as at least 5 feet, 11.7 inches -- had a 2.57 times higher risk
• Obese, short men had a 2.11 times higher risk.

Women were defined as short if they were 5 feet 2.6 inches or less. Normal-weight again was defined as having a BMI below 25; obesity was defined as a BMI of 30 or higher.

Compared to short, normal-weight women:

• Obese, tall women -- anyone more than 5 feet, 6 inches -- had a 2.77 times higher risk of clots
• Obese, short women had a 1.83 times higher risk
• Normal-weight, tall women had no increased risk