Caffeinated beverage intake and reproductive hormones among premenopausal women in the BioCycle Study

Abstract

Background: Caffeinated beverages are widely consumed among women of reproductive age, but their association with reproductive hormones, and whether race modifies any such associations, is not well understood.

Objective: We assessed the relation between caffeine and caffeinated beverage intake and reproductive hormones in healthy premenopausal women and evaluated the potential effect modification by race.

Design: Participants (n = 259) were followed for up to 2 menstrual cycles and provided fasting blood specimens for hormonal assessment at up to 8 visits per cycle and four 24-h dietary recalls per cycle. Weighted linear mixed models and nonlinear mixed models with harmonic terms were used to estimate associations between caffeine and hormone concentrations, adjusted for age, adiposity, physical activity, energy and alcohol intakes, and perceived stress. On the basis of a priori assumptions, an interaction between race and caffeine was tested, and stratified results are presented.

Results: Caffeine intake ≥200 mg/d was inversely associated with free estradiol concentrations among white women (β = -0.15; 95% CI: -0.26, -0.05) and positively associated among Asian women (β = 0.61; 95% CI: 0.31, 0.92). Caffeinated soda intake and green tea intake ≥1 cup/d (1 cup = 240 mL) were positively associated with free estradiol concentrations among all races: β = 0.14 (95% CI: 0.06, 0.22) and β = 0.26 (95% CI: 0.07, 0.45), respectively.

Conclusions: Moderate consumption of caffeine was associated with reduced estradiol concentrations among white women, whereas caffeinated soda and green tea intakes were associated with increased estradiol concentrations among all races. Further research is warranted on the association between caffeine and caffeinated beverages and reproductive hormones and whether these relations differ by race.

FIGURE 1.

Percentage of women consuming caffeinated, decaffeinated, and/or decaffeinated/noncaffeinated beverages based on average intakes captured by eight 24-h dietary recalls across 2 menstrual cycles (n = 259). Caffeine sources—based on total caffeinated food, beverage, or medication items reported—are also shown (n = 3079).

FIGURE 2.

Adjusted mean serum concentrations of free estradiol across the menstrual cycle for white and Asian women according to caffeine and caffeinated coffee intakes (n = 277 cycles for whites and n = 64 cycles for Asians). The analyses were conducted by using nonlinear mixed models with harmonic terms centered on the day of ovulation. Display set: women with a mean age of 27 y, waist-to-hip ratio of 0.75, perceived stress of 20.2, daily exercise of 14.7 min, and energy intake of 1614 kcal who were consumers of alcohol.

FIGURE 3.

Adjusted mean serum concentrations of total and free estradiol across the menstrual cycle according to intake of caffeinated soda (n = 467 cycles). The analyses were conducted by using nonlinear mixed models with harmonic terms centered on the day of ovulation. Display set: women with a mean age of 27 y, waist-to-hip ratio of 0.75, perceived stress of 20.2, daily exercise of 14.7 min, and energy intake of 1614 kcal who were consumers of alcohol.