Blue-collar workers are more likely to die of heart disease than are white-collar workers, possibly because of "greater stresses," but the exact reason remains a mystery.

Researchers from the Harvard Medical School report that even accounting for differences between the groups in smoking, obesity and other coronary risk factors, blue-collar workers are still 43 percent more likely to die of heart ailments.

"We can't rule out that just being blue collar increases risk, that perhaps there are greater stresses involved, but we really need to look into the whole thing further," said Dr. Charles Hennekens of Harvard and the Brigham and Women's Hospital in Boston.

Hennekens, an author of the Harvard study in the current Journal of the American Medical Association, said he suspects subtle differences in diet, medical care and cultural factors may play a greater role in the increased heart disease risk than the jobs themselves.

The difference in the risk of heart disease has been apparent for more than a decade. It generally has been attributed to a burgeoning health consciousness among white-collar workers and a reluctance among blue-collar workers to give up smoking, fatty diets and a sedentary life style.

But Hennekens and his colleagues found that even after accounting for those coronary risk factors, blue-collar workers had a much higher risk of dying from heart disease, compared with white-collar workers.

In fact, in the study of 568 matched pairs of blue- and white-collar workers, the difference in risk was less before accounting for these factors because the white-collar workers were more likely to be overweight and Jewish, two factors significantly associated with heart disease.

All of the subjects in the study were white men between 30 and 70. Black men have a higher rate of heart disease than white men, and women and Asian men have a lower rate.

Despite the finding, Hennekens said, there is much a person can do short of changing jobs to reduce the risk of heart disease.

"The occupation thing is interesting, but the public health message doesn't change at all," he said. "Clearly, the important message here is whether you are a blue- or a white-collar worker at this time, the three greatest risk factors for heart disease are smoking, cholesterol level and blood pressure -- and those are all things that can be changed."