Adolescents, particularly black adolescents, who drink several soft drinks each day may increase their blood pressure and their risk for hypertension, according to a study published in the May issue of Archives of Pediatric & Adolescent Medicine.
"This paper indicates that the concern about soda consumption in children and teens should not be limited to the fact that soft drinks add more calories to the diet," says Dr. Margaret R. Savoca, nutritionist and postdoctoral fellow at the Medical College of Georgia and lead author on the study. "Caffeine consumption may also impact their blood pressure."
She noted that previous studies have shown caffeine's impact on blood pressure in adults but its impact on adolescent pressures has not been as extensively explored despite the fact that caffeine-consuming adolescents outnumber those who don't drink caffeine by two to one.
While she says the new findings provide another reason for parents to keep an eye on the amount of caffeinated drinks their children consume, they also point to the need for further exploration of the impact of this common stimulant.
"It is important to keep in mind that caffeine could also be a marker, an indicator of a lot of other practices that impact blood pressure," Dr. Savoca says. "I think probably our major take-home message is more research is needed to explore the relationship between rising rates of adolescent hypertension and soft drink consumption."
Dr. Savoca and her colleagues at MCG's Georgia Prevention Institute looked at the blood pressures and caffeinated-beverage intake of 159 healthy black and white adolescents ages 15 to 19.
The adolescents were enrolled in another MCG study, led by Dr. Gregory A. Harshfield, looking at blood pressure response to competitive stress, such as playing video games. That study enabled participants to choose from a wide array of foods commonly consumed by teens, then provided them with everything they ate and drank for three days. The only control was salt intake. Those three days were a good time for researchers to also look at caffeine consumption. Blood pressure readings were taken when participants were screened for the study.
They found that those who drank the most caffeine - more than 100 milligrams a day or the equivalent of about four 12-ounce sodas - had the highest pressures. The top or systolic number, which indicates the pressure inside blood vessels that the heart must beat against, was the most impacted.
They also found that despite the fact that the highest consumers who were white consumed even more caffeine than their black peers, the blacks' pressures were most impacted. Black adolescents who consumed the most caffeine had systolic pressures that averaged 13.9 millimeters higher than blacks who consumed less than 50 milligrams of caffeine; in adolescent whites, the average was only about .2 millimeters higher.
The researchers noted that they adjusted for other factors that might influence blood pressure such as sex and weight.
The remaining differences could be explained by the fact that blacks and whites have different mechanisms for blood pressure regulation, says Dr. Harshfield, physiological psychologist and a study author. He has shown that some black adolescents have a reduced ability to secrete sodium long after the stress - which prompted the body to retain more sodium in order to retain more fluid and maintain a higher blood pressure - is gone. "Somehow, caffeine is having an effect on casual blood pressure. We don't know how but it has to affect that system because it's the one driving the blood pressure," Dr. Harshfield says.
"The prevalence of hypertension among youth is rising," the researchers write in the Archives of Pediatric & Adolescent Medicine. "By adolescence, both African-American girls and boys have higher systolic blood pressure than Caucasians. To reduce the risk of hypertension among this vulnerable group, a better understanding of the environmental (including diet) and genetic factors that contribute to blood pressure differences between young African-Americans and Caucasians is needed. One such dietary factor is caffeine consumption," they write, noting that an estimated 68 percent of boys and 62 percent of girls ages 12 to 17 drink one or more soft drinks daily and about 20 percent of boys and girls drink tea or coffee every day.
To pursue that understanding, Dr. Savoca is tentatively slated to receive a National Institutes of Health grant this summer to compare study participants who had the lowest blood pressures and body weights with those with the highest. "We are going to take the kids we already have looked at, identify kids on the extreme and look at their lifestyle behaviors, their dietary behaviors, their understanding of hypertension. We also are going to look at their mothers to see if we can find a family link between behaviors. The focus will not be caffeine but really the overall understanding of what seems to be contributing lifestyle-wise and attitudinally to differences in risk," Dr. Savoca said.
The published study was funded by the National Institutes of Health.
Other study authors include research assistants Conner D. Evans and Martha E. Wilson and biostatistician David A. Ludwig.