Resist that cup of coffee at 3:00 in the afternoon, no matter how tempting it may be. Caffeine can have a disruptive effect on your sleep. The most obvious effect of the stimulant is that it can make it hard for you to fall asleep. The stimulant can delay the timing of your body clock. These effects will reduce your total sleep time and the amount of deep sleep that you enjoy. A study once found that consuming caffeine 6 hours before bedtime reduced total sleep time by 1 hour.