Due in large part to the popularity of energy drinks and chain coffee shops, caffeine intake by children and adolescents has risen substantially - some drinks are marketed to children as young as four.

Unlike nicotine, caffeine has slipped under the cultural radar as a harmless drug, even for kids, but some research is happening. A new paper about a small study says that after puberty, boys and girls experience different heart rate and blood pressure changes after consuming caffeine. Girls also experience some differences in caffeine effect during their menstrual cycles. 

The double-blind, placebo-controlled, dose-response study examined heart rate and blood pressure before and after administration of placebo and two doses of caffeine (1 and 2 mg/kg) in pre-pubertal (8- to 9-year-old; n = 52) and post-pubertal (15- to 17-year-old; n = 49) boys (n = 54) and girls (n = 47).

Other studies have found that caffeine increases blood pressure and decreases heart rate in children, teens and adults, including pre-adolescent boys and girls. The purpose here was to learn whether gender differences in cardiovascular responses to caffeine emerge after puberty and if those responses differ across phases of the menstrual cycle.

"We found an interaction between gender and caffeine dose, with boys having a greater response to caffeine than girls, as well as interactions between pubertal phase, gender and caffeine dose, with gender differences present in post-pubertal, but not in pre-pubertal, participants," says Jennifer Temple, PhD, associate professor in the Department of Exercise and Nutrition Sciences, University at Buffalo. "Finally, we found differences in responses to caffeine across the menstrual cycle in post-pubertal girls, with decreases in heart rate that were greater in the mid-luteal phase and blood pressure increases that were greater in the mid-follicular phase of the menstrual cycle.

They were looking exclusively into the physical results of caffeine ingestion.
Phases of the menstrual cycle, marked by changing levels of hormones, are the follicular phase, which begins on the first day of menstruation and ends with ovulation, and the luteal phase, which follows ovulation and is marked by significantly higher levels of progesterone than the previous phase. 

Future research could determine the extent to which gender differences are mediated by physiological factors such as steroid hormone level or by differences in patterns of caffeine use, caffeine use by peers or more autonomy and control over beverage purchases, Temple says. 

Jennifer Temple, University at Buffalo. Credit: University at Buffalo