Background: We have shown previously that male and female adolescents differ in their responses to caffeine, but to date, the mechanisms underlying these gender differences are unknown.
Objective: The purpose of this study was to test the hypothesis that differences in circulating steroid hormones mediate gender differences in response to caffeine.
Methods: Subjective and physiological responses to caffeine were tested in adolescents using a double-blind, placebo controlled, crossover design. Participants were tested every 2 weeks for 8 weeks and received placebo and caffeine (2 mg/kg) twice each. Females were tested with placebo and caffeine in each phase of their menstrual cycle. Salivary concentrations of testosterone, estradiol, and progesterone were also measured.
Results: Males showed greater positive subjective effects than females. In females, higher levels of estradiol were associated with little or no subjective responses to caffeine, but lower levels of estradiol were associated with negative subjective responses to caffeine relative to placebo. There were gender differences in cardiovascular responses to caffeine, with males showing greater decreases in heart rate after caffeine administration than females, but females showing greater increases in diastolic blood pressure than males after caffeine administration. These gender differences may be related to steroid hormone concentrations. Blood pressure responses to caffeine were lower in males when estradiol was high, but higher in females when estradiol was high.
Conclusions: When taken together, these findings suggest that males and females differ in their responses to caffeine and that these differences may be mediated by changes in circulating steroid hormones.