All of the men in my life love to give me a hard time about how much coffee I drink. And sure, I’ve been known to take down enough cold brew to lift a car or two. But it’s not my fault I need an endless drip of java to keep me awake through the day. In fact, according to science, men are just caffeine lightweights who can’t keep up.
The caffeinated gender gap was first identified by a team of researchers from the University of Barcelona in 2008 who recruited a sample of 668 college students to examine how caffeine affects both genders. Participants were randomly assigned to drink caffeinated or decaf coffee with either 100 milligrams or 5 milligrams of caffeine, between the hours of 11 a.m. and 1 p.m., and again between the hours of 4 p.m. and 6 p.m. Afterwards, researchers asked them about their overall energy level and alertness.
“Although both the men and women saw an improvement in their activity levels with the coffee, which increased in later measurements, we observed a greater impact among the males,” Ana Adan, lead author of the study, explained in a press release. While men feel the impact of coffee within 10 minutes of drinking it, Adan added that “45 minutes is the time needed for maximum caffeine concentration to be reached in the blood, but levels reach half this concentration after just a few minutes.”
As for why men may be more sensitive to caffeine, a follow-up study hypothesized that the sex hormone estradiol, an estrogen steroid hormone, could dull the female response. In addition to asking participants about how strongly they felt the effects, researchers also tested their blood pressure, heart rate and cortisol levels. Overall, “males showed greater positive subjective effects than females,” the authors noted. “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.”
Although men experienced stronger effects from caffeinated beverages, when it came to decaf, both studies found men and women experienced a small, immediate boost — likely a result of the placebo effect. Interestingly, they found that this effect was slightly stronger for women.
All of this should help explain why a shot of espresso gives you heart palpitations but your girlfriend can take a nap right afterward. So you might want to leave the double shots to the professionals.