The amount of caffeine consumed by teenagers is directly related to their daytime blood pressure - and this effect is especially pronounced among African Americans - researchers report.

The new findings, which are based on 24-hour measurements of blood pressure taken with a portable recorder, back up earlier research by the same investigators in which they used one-time readings of blood pressure.

In the latest study, 41 African-American and 41 white adolescents selected foods and beverages for a four-day sodium-controlled diet. The subjects were divided into three groups based on caffeine intake, and ambulatory blood pressure measurements were taken during one of the four days.

African-American participants had higher daytime and nighttime blood pressures than their white counterparts, Dr. Margaret R. Savoca, from the Medical College of Georgia in Augusta, and colleagues found.

In both groups, daytime blood pressure rose as caffeine intake increased, with a greater effect seen in African Americans. By contrast, caffeine intake was not associated with nighttime blood pressure, the researchers report in the American Journal of Hypertension.

“The present research highlights the need for additional studies that examine the direct effect of caffeine from beverages on adolescent blood pressure, and consider why caffeine’s effects may not be consistent across racial groups,” the team writes.

“If caffeine has a direct effect on blood pressure in youth at risk for hypertension, it may be possible to design relevant intervention strategies and offer a straightforward public health message that could help reduce the risk of hypertension among young African Americans and other vulnerable populations,” they conclude.

SOURCE: American Journal of Hypertension, January 2005.