Social stress linked to hypertension.

Social stress linked to hypertension

Blacks in the United States run a greater risk of high blood pressure than whites, a fact that has perplexed researchers attempting to unravel the genetic and environmental causes of hypertension.

A report in the Feb. 8 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION now indicates that a U.S. black's increased risk of having blood pressure higher than 160/95 depends partly on his or her social and economic status. "The message to take out of this is that we need to investigate the environmental factors related to the excess of high blood pressure in black Americans," says cardiovascular epidemiologist Michael J. Klag of the Johns Hopkins University School of Medicine in Baltimore.

Klag and his colleagues reexamined data from a previous study of stroke risk among 457 blacks in Savannah, Ga., Hagerstown, Md., and Pueblo, Colo. During that study, the researchers had measured the darkness of each participant's skin by recording the amount of light reflected from the surface of the upper arm. Klag's team used these skin color measurements as a "marker" of genetic inheritance in the hypertension study.

According to the laws of genetics, blacks with darker skin should have inherited more of their genes from dark-skinned West African ancestors, the researchers note. Previous work has indicated that genes passed down from these ancestors are associated with high blood pressure among U.S. blacks. Thus, the investigators reasoned, darker-skinned blacks should be more likely to have inherited genes that predispose them to high blood pressure.

When Klag and his colleagues compared skin color variations with blood pressure measurements, they found that blacks with darker skin did tend to have higher blood pressure -- but only if they also ranked low on an index for socioeconomic status or if they hadn't finished high school.

When the researchers looked only at participants who had graduated from high school or who ranked in the top third of the socioeconomic index, they found that having darker skin did not correlate with high blood pressure. This suggests that genes influencing high blood pressure in blacks may play only a weak role in the increased risk of hypertension among U.S. blacks, Klag says.

Variations in skin darkness also proved a weaker predictor of blood pressure -- regardless of socioeconomic status -- than other hypertension-linked factors the researchers measured, such as body weight or the amount of sodium and potassium in the diet.

Elijah Saunders, a cardiologist at University of Maryland in Baltimore, says the study helps confirm the presence of a strong social or environmental component to hypertension in U.S. blacks. "It may not be all genes and hormones," he says, "although those things may be the background for it."

Other researchers have repoted a link between high blood pressure and low socioeconomic status for both blacks and whites, Klag says. However, his team's analysis controlled for other possible causes of high blood pressure among low-income people (such as weight and diet), suggesting that the stress of unemployment, racism and poverty could be the culprit, he says.

Michael G. Ziegler, a hypertension researcher at the University of California, San Diego, notes that studies have consistently shown a link between suppressed hostility and high blood pressure in both blacks and whites.

Yet Ziegler suggests that researchers may have difficulty pinning down the stresses of poverty and racism as causes of high blood pressure. For one thing, he says, investigators are limited by cultural biases that could complicate their assessments of how much stress a person feels.