Poor, darker-skinned blacks may be more susceptible to high blood pressure than other blacks, says a newly published Johns Hopkins study that relates the racial stresses of being black to hypertension.
The study, published in today's Journal of the American Medical Association, of 437 blacks living in Maryland, Colorado and Georgia suggests that environment -- specifically poverty -- outweighs genetics in determining high blood pressure in blacks.
Darker skin color is a marker for greater racial discrimination and that discrimination is stressful enough to induce more hypertension among those without jobs and education, according to Dr. Michael A. Klag, an assistant professor of medicine and the study's lead author.
Klag further said, "If genes are responsible for high blood pressure, we should have seen higher blood pressure associated with skin color across-the-board, regardless of levels education and income."
He firmly believes that more research is needed to see why poorer people have high blood pressure and what role stress plays in the lives of darker-skinned blacks because of their color.
"If you say something is genetically mediated, there is the connotation that if it's genetic, you can't do much about it," he said in an interview yesterday. "But, if it's environmental, then you can identify those environmental factors and make them better."
Compared with whites, blacks have almost twice the risk of having high blood pressure and more blood pressure-related disease. Previous studies have shown that most of that is due to differences in socioeconomic status between whites and blacks and to poor access to health care.
The Hopkins study, which is not the first to show that high blood pressure and skin color are linked among poor blacks, was cited by Dr. Robert J. Murray of the Howard University College of Medicine for its examination of "the blood pressure-skin pigmentation association in a much more controlled fashion."
The study was based on data just recently analyzed but collected in the early 1970s by a Hopkins group that was researching stroke, another debilitating condition.
Dr. Elijah Saunders, a University of Maryland Medical Center expert on high blood pressure in blacks who himself did a study of the link between blood pressure and skin color in the 1970s, questioned whether the findings would be the same if studies were done in 1991.
"The discrimination-stress related factor was much bigger at that time," he said, "and reporting this kind of sensitive information then would not have been very popular. More up-to-date studies might find that discrimination does not exist to the same extent as it did in the '70s.
"It is also felt by many blacks, like myself, that in the '60s and '70s and even before that time, discrimination against darker-skinned blacks was not only being practiced by other races but by blacks themselves," Saunders said. "That was before the days of 'Black is beautiful.' "
He further said that everyone agrees that some mix of genetic and environmental influences exists, but, "I side with the fact that there is probably more to the genetic predisposition than the environmental considerations. We see so much [hypertension] in blacks and in all socioeconomic levels."
But, in an accompanying editorial in JAMA, Murray wrote, "The fact that skin pigmentation and blood pressure are not consistently linked is evidence that they are not genetically linked.
"A combination of socioeconomic status and a behavior pattern of repressed hostility in a dark-skinned individual may be the . . . marker of the at-risk person," he said.