Coffee a-gender

It may not be fashionable to say it, but there are differences between women and men. This is not about what constitutes a “clean” room, and nor is it about the relative merits of theatre and rugby; it is about biology as a new study shows that women and men are quite different in the way they are affected by caffeine.

As background to this study, we need to know that previous research has shown that caffeine increases blood pressure and decreases heart rate in children, teens, and adults. If it seems counterintuitive that a stimulant like caffeine could decrease heart rate, the theory is that immediately you consume it caffeine does have a direct stimulating effect on the heart but this causes a reflex dropping in heart rate via nerve sensors called “baroreceptors” located in blood vessels. The end result is that after an initial increase there is a decrease in heart rate for about 75 minutes after the amount of caffeine in a cup of coffee, even though blood pressure increases.

With that as background, what these researchers wanted to establish was whether there is a gender difference in the effects of caffeine in teens or young adults.

To do this they measured heart rate and blood pressure in girls and boys aged 15-17 after either a placebo or two doses of caffeine at the ratio of either one or two milligrams per kilogram of bodyweight.

The results showed that there were gender differences. Boys had a greater response to caffeine generally but this only applied when the person had gone through puberty. There was no sex difference when the tests were done on subjects aged 8-9.

Additionally, there were changes in how girls responded to caffeine depending on where they were in their menstrual cycle. It was found that after ovulation, when progesterone levels were higher, there was a greater increase in blood pressure and decrease in heart rate for girls compared to when they were in the first phase of their cycle.

It does seem that there is a hormonal link here but the researchers say it might also be psychosocial factors like differences in patterns of caffeine use, peer consumption of caffeine, or control over drink purchases that play a role.

Whatever the reason though, it does seem that coffee’s wisdom knows no bounds as it too recognises the difference between the sexes and how they express (or should that be espresso?) themselves.