Research shows that coffee affects men and women in vastly different ways

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If a meeting becomes stressful, does it help, or make things worse, if team members drink lots of coffee?

A study by Lindsay St. Claire and colleagues that set out to answer this question has uncovered an unexpected sex difference.

For two men collaborating or negotiating under stressful circumstances, caffeine consumption was bad news, undermining their performance and confidence. By contrast, for pairs of women, drinking caffeine often had a beneficial effect on these same factors. The researchers can't be sure, but they think the differential effect of caffeine on men and women may have to do with the fact that women tend to respond to stress in a collaborative, mutually protective style (known as 'tend and befriend') whereas men usually exhibit a fight or flight response.

The study involved 64 male and female participants (coffee drinkers at the University of Bristol with an average age of 22) completing various construction puzzles, negotiation and collaborative memory tasks in same-sex pairs. They did this after drinking decaffeinated coffee, which either had or hadn't been spiked covertly with caffeine (the equivalent of about three cups' worth of coffee). Stress was elevated for some of the pairs by telling them they would shortly have to give a public presentation, and by warning them that their participation fee would be performance dependent.

How large were the caffeine effects? The men's memory performance under stressful conditions with caffeine was described by the researchers as 'greatly impaired' whereas caffeine didn't affect women in the same situation. For the construction puzzles, caffeine under high stress conditions led men to take an average of twenty seconds longer (compared with no caffeine) whereas it led women to solve the puzzles 100 seconds faster.

A short-coming, acknowledged by the researchers, was that there were overall few effects of stress on the participants' performance, no doubt in part because they'd been told they could bail out any time they liked (although none of them did). Further research is clearly need to replicate the findings and explore the possible underlying mechanisms. Such work is urgent, the researchers concluded, 'because many ... meetings, including those at which military and other decisions of great import are made, are likely to be male-dominated. Our research suggests that men's effectiveness is particularly likely to be compromised. Because caffeine is the most widely consumed drug in the world, it follows that the global implications are potentially staggering.' 

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