It's 1: 45 a. m, and 21-year-old Thomas Murphy is studying for an important exam. To stay awake, he's had two cups of coffee in the last three hours and is now downing a popular energy drink which also has caffeine.
Caffeine is present in many of the foods and drinks we consume (消耗), but is it good for us? Charles Czeisler, a scientist and sleep expert at Harvard Medical School, believes that caffeine causes us to lose sleep. "Without enough sleep — the typical eight hours -the human body will not work at its best, physically, mentally, or emotionally. " Too often, Czeisler says, we consume caffeine to stay awake, which later makes it impossible for us to get the rest we need.
A number of scientists believe that regular caffeine use causes physical dependence. Heavy caffeine users show similar behaviors. For example, they get mild to severe headaches, or they feel tired or sad when they can't have a caffeinated drink. To reduce or stop these feelings, users must consume caffeine, which is characteristic of drug addiction.
Despite these concerns, the general opinion in the scientific field is that caffeine is not dangerous when one or two small cups of coffee per day are consumed. Furthermore, a lot of current research goes against long-held negative beliefs about caffeine, and suggests that it may, in fact, have health benefits. For example, studies have shown that caffeine can help ease pain and help improve one's mood. Research has also shown that some caffeinated drinks can help the body fight a number of illnesses, including certain types of cancer.
Caffeine's behavioral effects are real, but most often mild. Getting that burst of energy, of course, is why many of the world's most popular drinks contain caffeine. Whether it's a student drinking coffee before class or a businessperson enjoying tea with lunch, humankind's favorite stimulant (兴奋剂) is at work every day, all over the world.
