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Racial differences in heart rate.

Racial differences in heart rate

Black men have a faster heart rate than white men during moderate exercise, a finding that suggests blacks have a genetically different response to stress.

Lars G. Ekelund of the University of North Carolina at Chapel Hill and his colleagues analyzed the results of a 6-minute treadmill test taken by 2,548 white men and 83 black men aged 20 to 69 who participated in a nationwide study. Even after controlling for age, weight, typical physical activity and smoking, the team found that blacks walking on a slightly inclined treadmill at a rate of 2.5 miles per hour had an average heart rate of 139.6 beats per minute, nearly 8 beats per minute faster than that of whites taking the same test. The researchers found no racial differences in resting heart rate.

Ekelund's previous research showed that black males had higher blood pressure than white males during moderate exercise. Taken together, the studies may help explain why U.S. blacks run a 33 percent greater risk of hypertension than whites. Over time, he explains, the increased heart rate and high blood pressure triggered by climbing stairs or other daily activities may stress the cardiovascular system, leading to chronic hypertension even at rest. High blood pressure is often called a "silent killer" because it puts people at risk for heart attacks and strokes.

Ekelund speculates that black males may have inherited a faster heart rate in order to clear heat efficiently from the body, a mechanism that would have been useful to their African ancestors. A rapid heart rate pushes more blood through the arteries, allowing excess heat to escape, he says.

His early research findings need to be confirmed with a larger study, Ekelund says. But he suggests that physicians evaluating treadmill test results keep in mind that black males may respond differently from whites for genetic reasons.
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Author:Fackelmann, Kathy A.
Publication:Science News
Date:Jul 1, 1989
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