Caffeine is safe and effective but not without a downside. Depending on one's sensitivity, it has a half-life of six to eight hours. Even if you have no trouble falling asleep after drinking coffee late in the day, you may wake more easily during the night because your nervous system is still aroused, your brain attuned to sounds and other stimuli that would otherwise go unheeded. The more poorly you sleep, the more caffeine you tend to consume the next day, and the more lightly you sleep the following night. And so on.
( Mary Roach )
[ Grunt: The Curious Science of ]
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