Tall people more likely to develop blood clots

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The taller you are, the more likely you may be to develop blood clots in the veins. In a study of more than 2m Swedish siblings, researchers found that the risk of venous thromboembolism – a type of blood clot that starts in a vein – as associated with height, with the lowest risk being in shorter participants.

They also found: for men shorter than 5’3,” the risk for venous thromboembolism dropped 65% when compared to the men 6’2″ or taller; and for women, shorter than 5’1″ who were pregnant for the first time, the risk for venous thromboembolism dropped 69%, compared to women that were 6 feet or taller.

“Height is not something we can do anything about,” said lead researcher Dr Bengt Zöller, associate professor at Lund University and Malmö University Hospital in Malmö, Sweden. “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.”

The CDC estimates venous thromboembolism affects up to 600,000 Americans every year, making it the third leading cause of heart attack and stroke. The most common triggers are surgery, cancer, immobilisation and hospitalisation. In women, pregnancy and use of hormones like oral contraceptive or estrogen for menopause symptoms are also important triggers.

Zöller said gravity may influence the association between height and venous thromboembolism risk. “It could just be that because taller individuals have longer leg veins there is more surface area where problems can occur,” Zöller said. “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 caution is that researchers didn’t have access to data for childhood and parent lifestyle factors such as smoking, diet and physical activity. In addition, the study consisted primarily of Swedish people and may not be translatable to the US population. Although, researchers note, the Swedish population nowadays is as ethnically diverse as the US population.

“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,” Zöller said.

Abstract
Background: Body height has been associated with an increased risk of venous thromboembolism (VTE), but the association can be confounded with shared familial factors (genetic/environmental). A cosibling design is useful for deeper understanding about the relationship between VTE and height.
Methods and Results: From Swedish national registry databases, we used a corelative design with full siblings alongside a general Swedish population sample. A cohort of male conscripts (n=1 610 870), born in 1951 to 1992 without previous VTE, was followed from enlistment (1969–2010) until 2012. Another cohort of first-time pregnant women (n=1 093 342) from the medical birth register, without previous VTE, was followed from first pregnancy (1982–2012) until 2012. Using the Multi-Generation Register, we identified all full-sibling pairs discordant for height. This cosibling design allowed for adjustment for familial factors (genetic/environmental). Compared with the tallest women (>185 cm) and men (>190 cm), there was a graded decreased risk by lower height for both men and women. The risk was lowest in women and men with the shortest stature (<155 and <160 cm, respectively): hazard ratios=0.31 (95% confidence interval, 0.22–0.42) and 0.35 (95% confidence interval, 0.22–0.55), respectively. There was a graded association also in the cosibling design comparing siblings with varying degree of discordance for height (reference was the taller sibling): ≥10 cm difference between brothers hazard ratios=0.69 (95% confidence interval, 0.61–0.78) and sisters hazard ratios=0.65 (95% confidence interval, 0.52–0.80), respectively.
Conclusions: Height is an independent predictor of VTE. The use of sibling pairs reduces the likelihood that familial confounding explains the results. The findings are important for the understanding of the pathogenesis of VTE.

Authors
Bengt Zöller, Jianguang Ji, Jan Sundquist, Kristina Sundquist

American Heart Association material
Circulation: Cardiovascular Genetics abstract


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