Coffee has been a part of people’s lives for thousands of years, and today it is still one of the favorite drinks in the world.Many people in the world begin their busy day by drinking a cup of coffee or several cups of coffee.They have always said that a cup of coffee in the morning helps them begin their day in the right way.So they say a cup of coffee is necessary for them in the morning. Do you know what in the coffee makes our bodies and brains active? It is caffeine(咖啡因).Caffeine may increase a person’s mental and physical abilities(精力和体力).For example, two cups of coffee will make you breathe faster and augment body temperature.All this makes your heart beat faster, and doctors warn that this may be a little dangerous. Caffeine is found in tea, coffee, chocolate and some other foods .A little caffeine is probably not harmful.But too much caffeine can make people nervous and sleepless.