In a study that is sure to fan an age-old scientific debate, Johns Hopkins researchers have attributed the high rates of hypertension among blacks to the stresses of living with racism, poverty and low educational levels -- not to genes.
The scientists did not entirely dismiss a genetic link but suggested that stress is the leading reason why blacks suffer disproportionately from high blood pressure -- a disease that is major contributor to heart failure, kidney disease and strokes.
"We live in a race-conscious society, where darker skin color is probably a marker for exposure to psycho-social stress," Dr. Michael A. Klag, the lead investigator, said in an interview yesterday.
The study, described in today's Journal of the American Medical Association, found that hypertension was common among dark-skinned blacks who lacked jobs or a high school education. But the disease was far less common among dark-skinned blacks with higher educational and income levels.
If genes were the predominating factor, Dr. Klag said, the health problem should persist equally among both groups -- regardless of economics or education.
The article won praise yesterday from Dr. Benjamin L. Hooks, executive director of the National Association for the Advancement of Colored People, who said that the study "gives scientific support to something we have known for generations -- it's not easy being black in America."
"If you are born black in this country, the unfortunate fact is that stress is a part of your life," Dr. Hooks said. "Others may find this difficult to believe, but if you look at our cultural heritage -- our poetry, songs, prose and arts -- you will find much of it is concerned with the dichotomy of being black in a race-conscious society."
Some scientists, however, said that the weight of scientific evidence from a variety of studies suggests that genetic factors predispose blacks to high blood pressure.
For many years, scientists have been trying to sort out the reasons why hypertension strikes blacks twice as often and five to seven times as severely as it does people of other races. The International Society on Hypertension in Blacks estimates that two-thirds of blacks over age 50 have high blood pressure.
The study relied on data collected in the early 1970s by a Hopkins-led team that was researching another ailment: stroke. Researchers studied 437 blacks in Hagerstown, Savannah, Ga., and Pueblo, Colo. -- measuring their blood pressure while taking information about their income, education and employment status. And they took another measurement: the darkness of their skin pigmentation. Geneticists, according to Dr. Klag, have long believed that darker skin represents a greater proportion of African genes -- while lighter skin suggests that a mixture of African and Caucasian genes.
In the hypertension study, the researchers figured that the volunteers with the darkest pigmentation should have the highest blood pressure if genes truly play the major role. The results were mixed.
For instance, hypertension was common among dark-skinned blacks who lacked a high school education -- but far less common among dark-skinned blacks who graduated from high school. Hypertension was less common among light-skinned blacks, whether or not they had gone to high school.
Dr. Klag said he expects his study to arouse controversy because of its use of skin pigmentation as an indicator of genetic makeup.
"Some people would argue that any research that looks at race is by definition racist and shouldn't be done," he said. "I don't think that, but I do think the results have to be looked at very carefully and not misinterpreted. We have to realize this is a sensitive social issue."
So far, the debate is dividing along scientific lines.
Dr. Elijah Saunders, a black physician who is president of the International Society on Hypertension in Blacks, said blacks more commonly than whites are plagued by kidneys that conserve rather than excrete salt. Salt retention, in turn, is a known factor in hypertension.
"Everybody agrees there is some mixture" of genetic and environmental influences, said Dr. Saunders, a hypertension expert at the University of Maryland School of Medicine. "But I side with the fact that there's probably more to the genetic predisposition than the environmental considerations. We see so much [hypertension] in blacks, and in all socio-economic levels. And in African people who are subjected to environmental stress."
Even one of the study's co-authors came to different conclusions.
"The great majority of hypertension seems to have genetic underpinnings," said Dr. Clarence E. Grim, a professor at the Charles R. Drew University School of Medicine in Los Angeles. Studies have shown that black and white people around the world whose diets are high in salt suffer disproportionately from hypertension -- but blacks more so than whites, he said.
The stresses of racism may raise the blood pressure of blacks who have already inherited a genetic predisposition to the disease, he said.