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Fitness lowers young blacks' blood pressure.

Fitness lowers young blacks' blood pressure

Physically fit black adolescents have lower nighttime blood pressure readings than their less-fit black peers, according to new research. The study hints that U.S. blacks can take steps early in fe to reduce the threat of cardiovascular damage caused by longstanding elevations in blood pressure.

Gregory A. Harshfield of the University of Tennessee in Memphis discovered racial differences in 24-house blood pressure patterns several years ago. He observed that blood pressure drops about 10 percent during sleep for white children, but black children show only about a 5 percent drop per night. The trend seems to worsen with age, and by adulthood, blacks have nocturnal blood pressure that remains at daytime levels. These findings suggest the artery-pounding pressure experienced at night in young blacks is a precursor of the hypertension that places them at a high risk of heart disease and stroke.

Harshfield's new report suggests black children can reduce their future risk of hypertension and heart disease with aerobic workouts. He presented his results in Cleveland this week at the 43rd Annual Conference and Scientific Sessions of the American Heart Association Council on High Blood Pressure Research.

Harshfield and his colleagues studied 175 healthy black and white boys and girls aged 9 to 18. They classified the youths as fit or unfit by measuring their ability to use oxygen while riding a stationary bicycle. The researchers recorded blood pressure for 24 hours, finding that physically fit black boys had average nighttime systolic pressure readings of 107 millimeters of mercury (mm Hg), while unfit black boys had blood pressure values averaging 118. Systolic pressure is exerted on arteries when the heart contracts.

Aerobic fitness seemed to reduce daytime blood pressure as well. Fit black males had systolic daytime readings of 117 mm Hg, whereas unfit black males had readings of 126.

Fit black girls showed similar reductions in both daytime and nighttime blood pressure compared with unfit black girls.

In contrast, fitness did not significantly alter blood pressure patterns among white boys and girls in the study. Fit white males, for instance, had an average systolic pressure of 120 mm Hg while awake, compared with 124 for unfit white males. Both fit and unfit white boys had nocturnal systolic values averaging 105 mm Hg.

The findings suggest that exercise alters a mechanism responsible for much of the hypertension commonly seen among blacks. Scientists have observed that blacks often have elevated levels of catecholamines, hormones that raise blood pressure by constricting blood vessels. Harshfield's research implies that exercise may help reduce blood pressure in blacks by lowering catecholamine levels or by reducing blood vessel sensitivity to these hormones. The different type of hypertension primarily seen in whites may not respond to exercise, Harshfield's work suggests.

He and other scientists believe U.S. blacks are genetically predisposed to high blood pressure because they conserve salt more efficiently than whites. But that inherited tendency needs an environmental trigger, such as a high-salt diet, to cause hypertension, Harshfield say. He suspects blacks experience high nocturnal pressure because the body is working overtime trying to clear the bloodstream of a high salt load.

But the blood pressure differences observed by Harshfield might be due to body weight or variations of pressure with age rather than fitness level, comments Darwin R. Labarthe of the University of Texas Health Science Center at Houston. And more work must be done to unravel the complicated interaction between genetic and environmental factors that seen to cause hypertension in blacks, adds Clarence E. Grim of the Drew/UCLA Hypertension Research Center in Los Angeles.
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Author:Fackelmann, K.A.
Publication:Science News
Date:Sep 30, 1989
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