When caffeine hits the body, blood pressure increases and heart rate decreases, past research has found. But the effects differ in males and females.
A recent study found that these differences in caffeine effects between the sexes appeared to emerge after puberty.
The study involved an experiment testing caffeine's effects in participants before and after puberty.
Boys appeared to have a stronger response to the caffeine than girls, though it was not entirely clear why.
The study, led by Jennifer Temple, PhD, of the School of Public Health and Health Professions at the University at Buffalo in New York, explored the differences in cardiovascular effects of caffeine between sexes in teens.
The researchers conducted an experiment with a group of 52 children aged 8 and 9 and 49 teens aged 15 to 17. Together, 54 boys and 47 girls participated.
Each participant was given a 1 mg/kg dose of caffeine, a 2 mg/kg dose of caffeine and a placebo dose (the participants did not know that there was no caffeine in this dose).
Before and after each dose, the researchers measured the participants' heart rate and blood pressure.
When the researchers compared the heart rate and blood pressure measurements before and after the doses, they found that caffeine had a greater effect on the boys.
However, this greater response to the caffeine among the boys was only true in the teens who had gone through puberty.
No differences between girls and boys were seen among the younger children in the study.
Meanwhile, the researchers found differences among the girls in how their bodies responded to the caffeine based on what part of their menstrual cycle they were on.
For example, the caffeine led to greater drops in heart rate among girls in the mid-follicular phase of the menstrual cycle.
During the follicular phase, the follicles in the ovary mature just before ovulation.
Meanwhile, blood pressure increases were greater in girls during the mid-luteal phase of the menstrual cycle.
The luteal phase occurs toward the end of the menstrual cycle, at the exact opposite time as the follicular phase in the cycle.
Therefore, the differences seen between males and females with caffeine's effects appears to occur only after puberty.
It is not clear, however, what it is about the different sexes or about puberty that plays a part in the different responses to caffeine.
"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.
The study was published June 16 in the journal Pediatrics. The research was funded by the National Institute on Drug Abuse. The authors reported no conflicts of interest.