Newswise — Caffeine elevates children's blood pressure and surprisingly lowers heart rate in children during exercise, but does not affect metabolism, according to new research from Harding University in Searcy, Ark.

The study is the first to investigate the effects of caffeine on both cardiovascular and metabolic responses to exercise in healthy boys and girls. Although the physical effects of caffeine have been studied for years, the effect of caffeine on children is still a new field of research.

The idea came to researcher Dr. Ken Turley, director of Harding's Human Performance Laboratory, when he drove past a kids' soccer tournament.

"All these kids are drinking sodas and energy drinks and I wondered what we knew about the effects of caffeine on kids, particularly during exercise," he says. "I found out we don't know that much."

In the study, published in the March issue of Medicine & Science in Sports & Exercise, by the American College of Sports Medicine, 52 seven to nine-year old boys and girls each randomly received a placebo and a caffeinated drink twice each on four separate days. An hour later, after taking resting measures, each child rode a stationary bicycle while blood pressure, heart rate and oxygen consumption were measured.

The results of the study demonstrate that caffeine acutely elevates both resting and exercise blood pressure, but acutely reduces heart rate in boys and girls given a moderate to high dose of caffeine an hour before exercise. The caffeine did not affect metabolism, nor were there significant differences found between boys and girls.

"We expected the increase in blood pressure," Turley says, "but the decrease in heart rate was surprising." He suspects it's the body's response to try to maintain a normal blood pressure.

"Long term caffeine intake has been associated with increased blood pressure in adolescents that increases the risk of hypertension," says Turley. "Although this study describes only an acute affect " the length of which is unknown " repeated exposure over days or weeks could contribute to possible long-term increases. Thus exposure to caffeine in young children should at best be limited, at least in children who are borderline hypertensive."

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Medicine & Science in Sports & Exercise (Mar-2006)