Monday, July 07, 2014
Caffeine is a drug millions of people turn to everyday to get that little push to get the day going but according to a recent study the impact it may be having on adolescent boys and girls is worth a closer look. Previous studies from our laboratory reported gender differences in the effects of caffeine in adolescents. The purpose of this study was to test the hypotheses that gender differences in cardiovascular responses to caffeine emerge after puberty and that cardiovascular responses to caffeine differ across the phases of the menstrual cycle.
New study finds 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.
Past studies have shown 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.
One researcher who is conducting such investigations is Jennifer Temple, PhD, associate professor in the Department of Exercise and Nutrition Sciences, University at Buffalo School of Public Health and Health Professions.
Temple says, “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.
“Finally,” she says, “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.
“In this study, we were looking exclusively into the physical results of caffeine ingestion,” she says.
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.
It’s possible that the changes in steroid hormones like testosterone and progesterone that occur during puberty change how caffeine is metabolized, the researchers said. Changes in caffeine consumption as kids get older could also explain the gender differences.
Future research in this area will 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.
"One potential explanation for this finding is that changes in steroid hormones that occur with pubertal development alter the metabolism of caffeine, which results in differential cardiovascular responses to caffeine in boys compared with girls," the authors wrote.
METHODS: To test these hypotheses, we examined heart rate and blood pressure before and after administration of placebo and 2 doses of caffeine (1 and 2 mg/kg) in pre-pubertal (8- to 9-year-olds; n = 52) and post-pubertal (15- to 17-year-olds; n = 49) boys (n = 54) and girls (n = 47) by using a double-blind, placebo-controlled, dose-response design.
RESULTS: There was an interaction between gender and caffeine dose, with boys having a greater response to caffeine than girls. In addition, we found interactions between pubertal phase, gender, and caffeine dose, with gender differences present in post-pubertal, but not in pre-pubertal, participants. Finally, we found differences in responses to caffeine across the menstrual cycle in post-pubertal girls, with decreases in heart rate greater in the midluteal phase and blood pressure increases greater in the midfollicular phase of the menstrual cycle.
CONCLUSIONS: These data suggest that gender differences in response to caffeine emerge after puberty. Future research will determine the extent to which these gender differences are mediated by physiological factors, such as steroid hormones, or psychosocial factors, such as more autonomy and control over beverage purchases.