Charles Czeisler, an expert on sleep and circadian rhythms at Harvard Medical School, put the matter starkly several years ago in a National Geographic article by T. R. Reid: The principal reason that caffeine is used around the world is to promote wakefulness. But the principal reason that people need that crutch is inadequate sleep. Think about that: We use caffeine to make up for a sleep deficit that is largely the result of using caffeine.
