Experiences of racial discrimination may be associated with blood pressure and contribute to differences in blood pressure among whites and blacks, according to a study by researchers at the Harvard School of Public Health.

Previous studies have found that blacks have a greater incidence of high blood pressure than whites, but the study was the first to examine how racial discrimination contributes to those differences.

The study, published in this month's American Journal of Public Health, divided black and white participants into four classes: working-class people and professionals, who have and have not experienced discrimination.

The study found that among working-class black women and men, higher blood pressure may be the result of suppressed or internalized responses to racial discrimination.

For black working-class women, blood pressure was the highest among those who said they generally reacted to discrimination by accepting it and keeping it to themselves. For men, blood pressure was the highest for those who said they accepted the unfair treatment but talked to others about it.

Working-class black men and women with the lowest blood pressure were those who said they faced only moderate discrimination, and their blood pressure was only slightly higher than their white counterparts.

Among black professional men and women, blood pressure was generally identical to that of their white counterparts.

The study suggested this may be the case because enhanced social and economic conditions among black professionals may contribute to a greater willingness to challenge racial discrimination, thus reducing their risk for hypertension.

For black professional women, blood pressure was lowest among those who faced moderate discrimination but took action against the unfair treatment. Black professional men who faced no discrimination or who faced moderate discrimination but took action against it had the lowest blood pressure.

The authors reported that the blood-pressure differences associated with racial discrimination are on par with differences that result from exercise habits, smoking or unhealthy diets.

"Public health researchers typically have treated 'race,' erroneously, as a biological variable and have rarely attempted to examine how people's experiences of and reactions to racial discrimination can affect health status, said Nancy Krieger, the lead author of the study, in a statement.

"In doing this study, we sought to understand how racial discrimination affects health in ways that may be modified by social class and gender," said Krieger, assistant professor at the Harvard School of Public Health. "This is profoundly different from approaches that treat 'race' as if it were some kind of inherent characteristic."

The study consisted of 4,086 black and white men and women ranging in age from 25 to 37. The participants are enrolled in an on-going community-based study, in several sites, of risk factors for cardiovascular disease.