Caffeine has a greater effect on men than women, and its effects start just ten minutes after it is drunk, according to a new study.

Researchers from the University of Barcelona measured the alertness levels of 668 university students throughout the day after drinking a cup of espresso coffee. The caffeine improved the activity levels of both genders, but had a greater impact on the men. Researchers also found that even a cup of decaffeinated espresso coffee caused a slight improvement in their subjects' alertness, but the effects of decaf coffee were more noticeable among the women. [Science Daily]

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