CHICAGO (REUTER) - Obese women, those with high blood pressure or women who smoke more than a pack of cigarettes a day run an increased risk of developing a blood clot in the lungs, researchers said. The finding came from a long-range study of more than 112,000 nurses whose health was checked periodically beginning in 1976. "Increased body mass index was associated with a strong and statistically significant elevated risk of pulmonary embolism. The level of risk increased as the body mass index increased," the report from Brigham and Women's Hospital in Boston said. Body mass index is a weight-to-height measure. A body weight index of 29, for example, could represent a woman who is five and a half feet (1.7 metres) tall and weighs 210 pounds (95 kg). The study found that women with an index reading of 29 were nearly three times more likely to suffer a lung blood clot as women who were not obese. Those who smoked 25 to 34 cigarettes a day were 1.8 times more likely to suffer a blood clot in the lung than non-smokers, and high blood pressure was associated with nearly twice the risk for blood clots, the study said. The study was published in this week's Journal of the American Medical Association.