Being Tall and Obese Increases Risk of Deadly Blood Clots

tall obese blood clotsKnut Borch and colleagues from the University of Tromso published a paper in the current issue of Arteriosclerosis, Thrombosis and Vascular Biology investigating the combined effect of obesity and body height on the risk of blood clots or venous thromboembolism (VTE).

VTE is a collective term including deep vein thrombosis (DVT) and pulmonary embolism (PE). It is the third most common cardiovascular disease (CVD) in the United States, and is potentially fatal. While obesity has long been known to be a risk factor for VTE, increased height has only recently been implicated. In this study, Borch et al. found that both obesity and tall stature increase the risk of blood clots, and that this effect may be synergistic, particularly in men. Statistical analyses they performed suggested the joint effect of obesity and tall stature on VTE risk was greater than the sum of the individual effects in both sexes.

The investigators collected height and weight data on 26,714 residents of Tromso, Norway, and followed them for an average of 12.5 years, during which time 461 VTEs were recorded. They also collected self-reported clinical data in questionnaires on other risk factors for VTE, such as age, smoking, diabetes, and estrogen hormone replacement therapy (in women only) and adjusted for these factors in the statistical analysis.

They found that, in men, the risk of VTE was 5.28 times higher in men who were tall (at least 5 feet, 11.7 inches tall) and obese (BMI >= 30 kg/m2) compared with normal weight men (BMI < 25 kg/m2) with short stature (5 feet, 2.6 inches or less). The risk of VTE was 2.57 times higher in normal-weight and tall men, and 2.11 times higher in obese and short men. For women, compared with short (5 feet, 2.6 inches or less) normal-weight women, the risk of VTE was 2.77 times higher in obese and tall women, 1.83 times higher in obese and short women and did not increase in normal-weight and tall women (more than 5 feet, 6 inches).

In understanding why obesity leads to an increased risk of blood clots (usually in the deep veins of the legs), it is that increased abdominal weight leads to increased pressure within the abdomen, which decreases the flow of blood from the veins in the legs back up to the heart. This can lead to stasis (pooling of blood in the legs), which then promotes blood clots. Another potential reason is that obesity is known to be a chronic inflammatory state, which promotes blood clots. The reason that increased height may lead to blood clots is also a mechanical one, in that the longer the route that blood has to travel back to the heart, the more potential for blood pooling and clot formation.

These new findings suggest that, in addition to other risk factors, both height and obesity should be considered when assessing risk of dangerous blood clots. Weaknesses of this study are that there are other VTE risk factors that were not controlled for, such as cancers and surgery, and that a person’s weight tends to increase over time, so the effect of this variable may be underestimated. The strengths of this study are that it was longitudinal, meaning that patients were followed over time, and the data was collected prospectively. In addition, there was a large number of participants, and they had excellent follow-up, since the town of Tromso is served by only one hospital.

We spoke with Dr Vafa Shayani of the Bariatric Institute of Greater Chicago. He told us: “This is an important study on the synergistic effects of obesity and height in increasing the risk of dangerous blood clots, one of the many health risks of carrying extra body weight. A five-fold risk of increased venous thromboembolism in tall, obese males, is particularly significant, and supports early, aggressive treatment of obesity in this group.”

The paper’s abstract is here.


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