Even low doses of caffeine — equivalent to what you'd find in a half to a full can of soda or a cup of coffee — had an effect on kids' blood pressure and heart rates.
And, interestingly, researchers found that the stimulant had more potent heart and blood pressure effects in boys than girls after puberty. The results were published Monday in the journal Pediatrics.
It's those kinds of cardiovascular effects that most worry experts, with some going so far as to say that they think caffeinated drinks should be eschewed until children hit their late teens.
"There are lots of things we can't do because we're not old enough or mature enough," said Dr. Kevin Shannon, a professor of pediatric cardiology and director of pediatric arrhythmia at the Mattel Children's Hospital of the University of California, Los Angeles. "Caffeine should probably be added to that list."
The new study examined the effects of low doses of caffeine in 52 children aged 8-9 and 49 children aged 15-17. In the younger kids, gender made no difference. But in the older group, the stimulant's effects were felt more strongly by the boys.
Caffeine slowed heart rates and increased blood pressure in all the children. Though the slowed heart rate might sound counterintuitive, it's not a new finding, said the study's lead author Jennifer Temple, an associate professor at the University of Buffalo's School of Public Health and Health Professions.
At low doses the heart slows down to compensate for rising blood pressure, Temple explained. At higher doses, the heart speeds up.
"This study shows that what we would consider to be a low dose of caffeine — what some might not think twice about giving to an 8-year-old — is having an effect on the cardiovascular system," Temple said. "And right now we don't have enough data in kids to know what the long term effects of repeated exposure to caffeine would be."
Image: Frozen coffee drink, via Shutterstock