A study offers new evidence that environmental factors like poverty, diet and the stress of racial discrimination could outweigh genetic factors in explaining the excessive rate of high blood pressure among black Americans.

The study of 457 blacks in Hagerstown, Md., Pueblo, Colo., and Savannah, Ga., examined the reasons blacks are 40 percent more likely to suffer from hypertension than whites.In an effort to find out whether genetic factors are responsible, the researchers studied the relationship between skin color and the incidence of hypertension.

They said skin color usually represents a genetic mixture from black and white ancestors, and ``black individuals with the darkest skin color have the highest percentage of black ancestors.'

As a result, if a genetic factor is at work, susceptibility to hypertension ``should increase continuously with increasingly darker skin color,' the researchers said.

In fact, however, they found that darker skin color is a predictor of hypertension among blacks of low socioeconomic status, but not for blacks who were well-employed or better-educated.

Thus, they concluded, environmental factors could outweigh genetic determinants of high blood pressure in blacks. Darker skin might subject individuals to more discrimination and stress than that suffered by lighter-skinned people.

Those factors, including those associated with poverty, like poor diet and exercise habits, appear to increase the risk of hypertension among darker-skinned blacks, the study suggests.

Dr. Michael J. Klag of the Johns Hopkins University School of Medicine in Baltimore, the principal researcher in the study, cautioned that the results apply to a group and not individuals, and he added that doctors should not consider skin color alone when making diagnoses.

``The study means we have to concentrate on environmental factors that may be causing hypertension, not color,' he said.

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