To determine pressure differences between black and white children and at what age those differences occur, Dr. Frank Treiber, vice president for research and study coauthor, measured the ambulatory blood pressures of almost 700 children 12 times during 15 years.

“Most previous studies have looked at a crosssection of people, and this 15year study allows us to look at one population over an extended period of time,” said Dr. Xiaoling Wang, genetic epidemiologist and the study’s lead author. “This helps us identify the age these problems begin to occur—as early as age 10.”

Ethnic differences were measurable in study subjects even after researchers controlled for factors such as height, body mass index, socioeconomic status and stressrelated coping strategies.

Interestingly, she said, tests of people of African descent who live outside the United States have shown normal nighttime blood pressure.

“That most likely means that the problem is not purely genetic and also is likely caused by environmental factors like salt intake and stress,” Dr. Wang said. “It has already been proven that stress causes sodium retention, but there could be also other factors. This study supports existing research and warrants further study of the causes for racial differences in blood pressure at an early age.”

Study coauthors included Dr. Coral Hanevold, a pediatric nephrologists; Dr. Joseph Poole, an MCG student; and Dr. Harold Snieder, an MCG biostatistician.