咖啡提神仅仅只是心里作用?

　　Many say their brains don't start working properly in the morning until they have had a cup of coffee. But the stimulating effect for which caffeine is famous for may be an illusion, say researchers。

　　In a study carried out by Bristol University recently, 379 people who abstained from caffeine for 16 hours before drinking either caffeine or a placebo (dummy drink) were tested for a range of responses afterwards. The researchers found little variance in levels of alertness among the volunteers。

　　Peter Rogers, from the university's department of experimental psychology and one of the leading authors of the study, said: "Our study shows that we don't gain advantage from consuming caffeine."

　　But what makes people feel different after a cup of coffee in the morning? The researchers say that it is because it reverses the fatiguing effects of overnight caffeine withdrawal。

　　Around half the volunteers drank little or no caffeine and the other half were medium-high caffeine consumers. All were asked to carry out a series of computer tasks to test their level of memory, attentiveness and vigilance. The medium-high caffeine consumers who received the dummy drink reported a fall in alertness and an increase in headaches, neither of which were reported by those who received caffeine。

　　However, their post-caffeine levels of alertness were no higher than those of no or low-level consumers who received a placebo. This suggests caffeine only brings coffee drinkers back up to "normal"。

　　The researchers said their findings could also apply to those who claim they rely on a morning cup of tea to get their brains going。