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Stanford Report, March 17, 1999

Study reveals ethnic differences in heart disease risk factors among youth


Heart disease is not colorblind. Not only are middle-aged African-Americans twice as likely to die from heart disease as middle-aged whites, but both African-Americans and Mexican Americans are more likely to be overweight and to have other risk factors that promote cardiovascular disease, such as high-blood pressure, physical inactivity and diabetes.

A new Stanford study of more than 7,600 children and young adults shows that ethnic differences in cardiovascular disease risk factors are apparent in grade-school children and persist into adulthood. What's more, the researchers found that ethnic inequalities remain even when differences in socioeconomic status are factored out.

"Our results highlight the need to start interventions for healthy lifestyles at early ages," said Marilyn Winkleby, PhD, a senior research scientist at the Stanford Center for Research in Disease Prevention and the lead researcher on the study. "Interventions should begin as early as kindergarten."

Winkleby and colleagues based their analysis on the Third National Health and Nutrition Examination Survey, a six-year assessment of the health and nutritional status of the U.S. population conducted by the National Center for Health Statistics. Using questionnaires and medical examinations, this study gathered data on the health, diet, demography and economic status of a representative sample of nearly 34,000 Americans.

From this database, Winkleby's group statistically analyzed information for 2,769 African-Americans, 2,854 Mexican Americans, and 2,063 whites between the ages of 6 and 24. They compared the prevalence of primary risk factors for cardiovascular disease among the three ethnic groups. Since the three groups also differed in average socioeconomic status, the researchers factored out this variable, using educational level of the head of household and family income as an indicator of socioeconomic status.

Winkleby's colleagues were Tom Robinson, MD, assistant professor of pediatrics; Jan Sundquist, PhD, a visiting scholar from Sweden; and Helena Kraemer, PhD, professor of psychiatry and behavioral sciences. They reported their results in the March 17 issue of Journal of the American Medical Association.

Differences in risk factors were apparent even in the youngest age group: 6 to 9 years. Black and Mexican American girls of that age were already heavier than their white counterparts, and this gap continued to grow throughout childhood and adolescence. In the 18 to 24-year age group, black and Mexican American women of average height (5 feet 4 inches) were 12 pounds heavier than white women of the same stature.

Black and Mexican American girls also get a higher percentage of their energy from fat than do white girls and are at higher risk of diabetes. Black girls also have higher blood pressure than white girls.

The picture was slightly different for boys. Black and Mexican American boys were at higher risk for diabetes, and black boys ate a fattier diet than white boys, but there were no significant differences in weight or blood pressure.

One sobering fact was the high rate of smoking among young white men and women, especially those with lower socioeconomic status. In the lowest socioeconomic group (head of household with fewer than 12 years of education), 77 percent of young white men and 61 percent of young white women were current smokers.

Although the differences between ethnic groups may have some genetic basis, focusing only on genetic causes would be a mistake, Winkleby noted. Some of the causes of heart disease may yet be unknown, she said. Cardiovascular disease, which can build for decades before manifesting as a heart attack or stroke, is an insidious collaboration between genes and lifestyle. The genes that increase the risk of cardiovascular disease will not be expressed without the right environmental conditions ­ an unhealthy lifestyle. "We don't have methods to change genes, but we do know how to change lifestyles. And we know how to promote and maintain healthy behaviors," Winkleby said.

She and her coauthors recommend ethnically diverse educational programs to teach the importance of heart-healthy behaviors.

The research was funded by grants from the American Heart Association, the U.S. Public Health Service and the Swedish Research Council. SR