Danish scientists have discovered there is a direct relationship between blood clots and weight distribution in middle-aged people.
The 10-year study found that weight on men's waistlines and women's hips increased the risk of clotting.
Around 60,000 people took part in the research which showed that the location of the weight was an important factor.
It revealed that blood clots in veins - venous thromboembolism (VTE) - were more likely to occur in men if weight was put on around the waist. But in women hip circumference was "positively associated" with VTE.
Marianne Tang Severinsen, lead author of the study and a researcher at Aarhus University Hospital in Aalborg, Denmark, said: "The implications to the public are that all types of obesity increase the risk for VTE, but the location of body fat also plays some unknown role.
"For health professionals, the implication is that all types of fat distribution should be taken into account when evaluating risk for VTE."
It is hoped the research will help physicians better diagnose the condition.
The study, which examined 27,000 men and 29,000 women aged between 50 and 64, challenges previous research suggesting large hip circumference might protect against arterial thrombosis.
"Our study clearly shows that this is not the case for venous thrombosis," the authors said in an article published in Circulation: Journal of the American Heart Association.