Blacks’ Blood Pressure Link Discounted : Health: Study finds no genetic connection to high levels that affect them more than whites. Social stress and diet are called more likely causes.
Socioeconomic and environmental factors, not genetic differences, account for the greater prevalence of high blood pressure in blacks as compared to whites, according to a study led by researchers at the Johns Hopkins University School of Medicine in Baltimore.
The study in today’s Journal of the American Medical Assn. examined data from 457 blacks on the darkness of their skin color, which the researchers said can be used as an indirect measure of the percentage of black ancestry.
The researchers found that darker skin pigmentation did not increase susceptibility to high blood pressure, except in blacks who had not graduated high school or otherwise had low socioeconomic status.
“It appears that there is not a genetic mechanism for the higher blood pressures in African-Americans compared to white Americans,” said Dr. Michael J. Klag, leader of the research team.
In the United States, blacks have 1 1/2 to 2 times the prevalence of high blood pressure of whites. For example, 33% of whites between 55 and 65 have high blood pressure, compared to 54% of blacks, Klag said.
If the theory of genetically determined susceptibility to high blood pressure in blacks was correct, researchers would expect the percentage of blacks with high blood pressure to increase continuosly with darker skin color, regardless of an individual’s socioeconomic status.
The researchers speculated that blacks with darker skin color and lower socioeconomic status might be more susceptible to “psychosocial stress in a race-conscious society” and that this chronic stress might raise their blood pressures. Dietary factors, such as high salt intake, low potassium intake and obesity also may play a role.
In an editorial for the medical journal, Dr. Robert E. Murray Jr. of Howard University College of Medicine in Washington suggested that “a combination of disadvantaged socioeconomic status and a behavior pattern of repressed hostility in a dark-skinnned individual” may indicate a black person who is at particular risk of developing high blood pressure.
Klag cautioned that skin pigmentation measurements were used as a research tool and that there is no medical reason for individuals to have their skin color measured.
“On average, African-Americans who have darker skin color will have a higher proportion of their genes from the African gene pool, but there is a great deal of variability for any given individual,” Klag said.
High blood pressure predisposes an individual to heart disease, strokes and kidney disease. It is generally thought that genetics as well as environment play a role in most cases of high blood pressure, but the genes that are responsible for blood pressure elevation are not well understood.
Five previous studies of the relationship between skin color and blood pressure, published between 1970 and 1981, produced conflicting results.
The new study was based on data collected in Savannah, Ga., Hagerstown, Md., and Pueblo, Colo., between 1972 and 1974, but only recently analyzed. The researchers said the data, collected as part of study of strokes, was more detailed and less prone to bias than the data used in the other studies.
Skin color was measured on the inner part of the upper arm (to avoid darkening of the skin caused by sun exposure) with a device called a reflectometer. “More darkly pigmented skin reflects a lower percentage of light and yields a lower reflectance reading,” the report said.
Other researchers involved in the study were Josef Coresh and Dr. Paul K. Whelton of Johns Hopkins, Dr. Clarence E. Grim of the Drew Medical Center in Los Angeles, and Dr. Lewis H. Kuller of the University of Pittsburgh.
