Obesity boosts the risk of venous thromboembolism - the formation in veins of blood clots that can travel to the lungs - and is a particularly strong risk factor among men and women under 40 years old, according to a new report.

Obesity was first tied to fatal lung clots (aka, Pulmonary embolisms) in 1927, Dr. Paul D. Stein of St. Joseph Mercy Hospital in Pontiac, Michigan, and colleagues note in the American Journal of Medicine. There is also evidence that excess weight may also increase the risk of Deep venous thrombosis. But there have been a number of difficulties in verifying this association.

To investigate whether Obesity is in fact a risk factor for venous thromboembolism, Stein and his team reviewed 1979-1999 data from the National Hospital Discharge Survey, which included discharge information for more than 12 million obese patients and nearly 700 million patients not classified as obese.

Obese patients were 2.5 times more likely to have Deep venous thrombosis than non-obese individuals, and 2.21 times more likely to suffer a Pulmonary embolism. As past research has suggested, women’s risk of Deep venous thrombosis was somewhat greater than men’s.

The effect of Obesity rose substantially among individuals younger than 40, who had a more than 5-fold greater risk of Deep venous thrombosis or Pulmonary embolism compared with older patients.

Again, this risk was greater among women, with obese females under 40 having a 6-fold increased risk of Deep venous thrombosis compared to non-obese young women.

Because the diagnosis of Pulmonary embolism is frequently missed, Stein noted in a press release accompanying the study, the findings should “alert physicians to the possibility of this diagnosis” in obese patients.

SOURCE: American Journal of Medicine, September 2005.