Caffeine and caffeinated beverages may either increase or decrease serum estradiol concentrations in healthy premenopausal women, apparently depending on the race.
This study investigated the relationship between caffeine and caffeinated beverage consumption and reproductive hormones in premenopausal women of different races. Using validated food questionnaires, researchers examined the diets of 259 subjects for 2 months. The plasma estradiol concentrations of all the subjects were also measured.
Consumption of considerable amounts of green tea and caffeinated soda was observed to elevate estradiol concentrations in all races. The result of this study shows that consuming reasonable quantities of green tea and caffeinated soda is associated with high plasma estradiol levels in all races, but moderate intake of caffeine may decrease blood levels of estradiol in white women. Researchers observed that serum concentrations of free estradiol reduced with moderate intake of caffeine in Caucasian women but increased in Asian women.
Hopefully we will see more studies on this to understand why Caffeine elevates estradiol concentrations for all races but somehow "moderate" intake lowers estradiol concentrations for caucasian women.