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This study examined heart rate and blood pressure before and after af placebo or 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).

Caffeine affects boys and girls differently in puberty

Caffeine intake by children and adolescents has been rising for decades, due to marketing to children as young as four. Despite this, there is little research on the effects of caffeine on young people.

Jennifer Temple, PhD is conducting such an investigation. She is an associate professor in the Department of Exercise and Nutrition Sciences, University at Buffalo School of Public Health and Health Professions.

Temple's new study finds that after puberty, boys and girls experience different heart rate and blood pressure changes after consuming caffeine. Girls also experience differences in caffeine effect in their menstrual cycles.

The study, "Cardiovascular Responses to Caffeine by Gender and Pubertal Stage," is published in the journal Pediatrics.

Past studies, some by this research team, show that caffeine increases blood pressure and decreases heart rate in children, teens and adults, including pre-adolescent boys and girls. The current research is to learn whether gender differences in cardiovascular responses to caffeine emerge after puberty and how 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 we found interactions between pubertal phase, gender and caffeine dose, with gender differences present in post-puberty, but not in pre-pubertal, participants.

"Finally,we found differences in responses to caffeine across the menstrual cycle in post-puberty girls, with decreases in heart rate greater in the mid-luteal phase and blood pressure increases greater in the mid-follicular phase of the menstrual cycle.

"In this study, we were looking exclusively at physical results of caffeine ingestion."

Jennifer Temple, PhD, associate professor, Department of Exercise and Nutrition Sciences, University at Buffalo, School of Public Health and Health Professions

Phases of the menstrual cycle are indicated by changing levels in hormones. The follicular phase begins on the first day of menstruation and ends with ovulation. The luteal phase follows ovulation and has significantly higher levels of progesterone than the follicular phase.

Abstract
BACKGROUND: Caffeine use is on the rise among children and adolescents. 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.

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 prepubertal (8- to 9-year-olds; n = 52) and postpubertal (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 postpubertal, but not in prepubertal, participants. Finally, we found differences in responses to caffeine across the menstrual cycle in postpubertal girls, with decreases in heart rate that were greater in the midfollicular phase and blood pressure increases that were greater in the midluteal 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.

This double-blind, placebo-controlled, dose-response study was funded by a grant from the National Institute on Drug Abuse of the National Institutes of Health.

Co-authors are Amanda M. Ziegler, project coordinator for the Nutrition and Health Research Lab, and graduate student Adam Gracyzk, both in the UB Department of Exercise and Nutrition Sciences, UB School of Public Health and Health Professions; Ashley Bendlin, undergraduate student in the Environmental Studies Program and the Department of Psychology, UB College of Arts and Sciences; Theresa Sion, undergraduate student in family nursing, UB School of Nursing; and Karina Vattana, who recently graduated with a BS in biomedical sciences, UB School of Medicine and Biomedical Sciences.

For an embargoed copy of the study, contact Noreen Steward, nstewart@aap.org, American Academy of Pediatrics Department of Public Affairs. For an interview with the lead author, contact Patricia Donovan, Office of Communications, University at Buffalo, 716-645-4602 or pdonovan@buffalo.edu.