Obesity and smoking may each raise a person’s risk of potentially dangerous blood clots in the veins, but certain other suspected risk factors seem to have no impact, a new study finds.

The study, reported in the journal Circulation, investigated risk factors for venous thromboembolism - blood clots in the veins, usually affecting the legs. If one of these clots travels to the lungs, creating what is called a Pulmonary embolism, it can prove fatal.

Some studies have suggested that venous thromboembolism, or VTE, has largely the same risk factors as heart disease does, such as High cholesterol, diabetes, high blood pressure and smoking.

But most of those risk factors have not consistently been linked to VTE. Obesity has stood as the only condition strongly linked to both VTE and cardiovascular disease - including heart disease and peripheral artery disease, a hardening and narrowing of the arteries supplying the legs.

In the new study, researchers found that among nearly 19,000 Danish adults followed for 20 years, those who were obese or heavy smokers had an increased risk of developing VTE (a clot in a deep vein or a Pulmonary embolism).

Compared with non-smokers, those who smoked 25 cigarettes a day or more had a 52 percent greater risk. Meanwhile, obese adults were 65 percent more likely than the thinnest men and women to develop VTE, while severe obesity was linked to a doubling in the risk.

“The main message for the public from our study is that losing weight and quitting smoking are likely to not only reduce the risk of coronary heart disease and peripheral artery disease, but also of venous thromboembolism,” lead researcher Dr. Anders G. Holst, of University Hospital Rigshospitalet in Copenhagen, told Reuters Health in an email.

On the other hand, the study found no evidence that diabetes, exercise levels, High cholesterol or high triglycerides (another type of blood fat) were linked to an elevated VTE risk. And while elevated diastolic blood pressure appeared to be a risk factor, a diagnosis of high blood pressure was not. That raises the possibility that the former finding was due to chance, and not a true effect, according to the researchers.

The findings come from a long-term study begun in 1976, looking at heart disease risk factors among adults age 20 and older living in Copenhagen.

Of 18,954 study participants followed for 20 years, 969 had at least one VTE during that time. Obesity and current smoking remained linked to higher risks even after the researchers accounted for age, sex and other health factors.

The findings suggest that two already-recommended lifestyle changes - shedding excess pounds and quitting smoking - are key in lowering VTE risk, according to Holst.

He also noted that the lack of a link between cholesterol and VTE is interesting, as a recent clinical trial of the cholesterol-lowering drug rosuvastatin (Crestor) found a lower risk of VTE among patients using the medication.

The current findings, Holst said, suggest that the benefit did not come from cholesterol-lowering, per se, but from some other effect of statins.

SOURCE: Circulation, online April 19, 2010.