Many people rely on a cup of coffee or tea to start the dayand a glass of wine in the evening to "wind down." But both caffeine and alcohol interfere with sleep architecturecaffeine advances the time of REM sleep, interrupts consolidated sleep and reduces Stage 3 and 4 sleep, while alcohol reduces the total length of the sleep cycle and the amount of REM sleep.
In some people, caffeine takes only three to four hours to clear from the body, so an after-dinner cup of coffee or tea won't pose a problem. In others, however, it may take as long as 10 hours to clear, which means that "no caffeine after lunch" must become the new rule. Remember that caffeine is present not only in the usual suspects (regular tea, coffee and cola) but also in green tea, decaffeinated coffee and chocolate.