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Time Your Caffeine Consumption

Caffeine Timing (0:42)

Andrew Phillips, PhD, of Harvard, tells how long caffeine remains active in the body, and when to consume it to boost alertness.

Most people start to feel the alerting effects of caffeine in 15 to 30 minutes. Caffeine boosts alertness for as long as six to seven hours in many people, and even longer in some.

If you get sufficient sleep, caffeine at breakfast will do little to boost your alertness. Most people feel foggy upon waking up. This sleepiness may take 10 to 30 minutes, and perhaps longer, to fade. Alertness normally rises within an hour of awakening. To maximize benefits of caffeine later in the day, skip coffee at breakfast, or drink decaf if you like the taste of coffee at that meal.

About eight hours after you awaken, expect a dip in alertness due to your body clock. This is a good time to enjoy a cup of coffee or other caffeinated drink. You should feel its alerting effects. 

After about 12 hours of wakefulness, consider what’s ahead in the rest of your waking day. If you need to stay alert on the job, caffeine can decrease the drive to sleep that has been building since you woke up, and help you stay awake longer. However, if you can manage without the caffeine, skip it. Caffeine within four to six hours of bedtime usually lightens sleep, awakens you more often, prompts bathroom visits, and shortens overall sleep time. Some studies suggest that caffeine within six hours of bedtime can rob you of an hour of sleep.

"I feel best when I exercise, nap, have lunch, and then consume some caffeine. I need to be alert when I go back to work."
-Kristin, locomotive engineer