Caffeine influenced teenagers'daytime blood pressure, especially among African Americans, according to a study reported in the American Journal of Hypertension (January 2005). The current study, which was based on 24-hour measurements of blood pressure taken with a portable recorder, supported earlier research by the same investigators in which they used one-time readings of blood pressure.

For the study, 41 African American and 41 Caucasian adolescents chose foods and beverages for a 4-day sodium-controlled diet. The participants were separated into 3 groups based on their caffeine intake, and ambulatory blood pressure measurements were taken during 1 of the 4 days. The results showed that both groups'daytime blood pressures increased as caffeine intake rose. A greater effect was seen in the African-American group. The researchers noted, however, that caffeine consumption was not related to nighttime blood pressure.