Teens who habitually drink lots of caffeine - mainly from soft drinks - tend to have higher blood pressure than other teens, researchers report.

The association between caffeine and blood pressure was most apparent in African-Americans, researchers report in the May issue of the journal Archives of Pediatrics and Adolescent Medicine.

The small study is not the final word on the subject of caffeine and high blood pressure, but it does highlight the need for studying the effect of soft drinks on blood pressure, according to an editorial that accompanies the study.

“There is still a lot to learn about diet and blood pressure, especially in children and adolescents,” Dr. Stephen R. Daniels of Children’s Hospital Medical Center in Cincinnati told Reuters Health.

“It appears that caffeine could be important, but we need to know more about what it does over a prolonged period of time,” said Daniels, who co-authored the editorial with Dr. Sarah C. Couch.

Daniels added that it is uncertain to what extent dietary changes, such as cutting back on caffeine or salt, can improve blood pressure that is too high.

More and more adolescents in the U.S. are developing high blood pressure. While caffeine is known to be a risk factor for high blood pressure, there is little research on the effect of caffeine in adolescents.

Adults may get most of their caffeine from coffee, but soft drinks are the major source of caffeine in adolescents. An estimated 68 percent of boys and 62 percent of girls aged 12 to 17 drink at least one soft drink per day.

Dr. Margaret R. Savoca and colleagues at the Medical College of Georgia in Augusta looked at the relationship between caffeine consumption and blood pressure in 159 black and white adolescents. For three days, the researchers limited the amount of sodium participants could have in their diet, but allowed access to the beverages of their choice.

Participants were divided into three groups based on how much caffeine they consumed.

African Americans in the group that consumed the most caffeine - about 4 cans of soda per day - had higher systolic blood pressure (the top number in a blood pressure reading) than other adolescents, including white teens in the high-caffeine group.

The relationship between caffeine and diastolic pressure (the bottom number in a blood pressure reading) was more modest. Both black and white teens in the high-caffeine group had higher diastolic pressure than teens in the middle caffeine group.

Differences in lifestyle, such as exercise, smoking and diet, could explain why caffeine consumption was more strongly associated with blood pressure in African Americans, according to the researchers, but they acknowledge that the reasons are uncertain.

Another possibility, Savoca and her colleagues note, is that African-American teens who drank lots of soft drinks may have had an increased sensitivity to caffeine compared with whites who drank even more caffeine.

The researchers conclude that more studies should be conducted “to separate the direct effect of caffeine on blood pressure from soft drink consumption as one of several lifestyle behaviors associated with the risk of (high blood pressure) among young African Americans.”

SOURCE: Archives of Pediatrics and Adolescent Medicine, May 2004.