It takes about 15 to 30 minutes for you to feel the effect of the caffeine, and the benefit will last for three to four hours, Rosekind says. “If you plan strategically to use the caffeine every few hours, you can keep yourself at a pretty good level of performance,” he says.
The best strategy: Have your caffeine and lie down for a 30-minute nap. You’ll wake up feeling refreshed, he says.
One caveat: When you finally stop drinking your caffeinated beverage, expect a crash. “The caffeine masks the sleepiness, [but] the sleepiness just keeps building up,” Rosekind says.
Turn Up the Light
Your body clock is attuned to the cycle of darkness and light, so bright light has an alerting effect.
“As people get more and more tired, they often find bright light unpleasant and they’ll deliberately turn the light off,” says Dinges. Instead, you should turn lights on and even step out into the sunshine, Drummond says.
Move Your Body
Taking a brisk walk or working out gets your blood moving. Exercise also boosts your brain power. “If you move your body, there’s automatic feedback from your muscles that goes to the central mechanism of the brain to improve alertness,” says Sharon Keenan, PhD, founder and director of the School of Sleep Medicine of the Stanford University Center for Excellence for the Diagnosis and Treatment of Sleep Disorders.
Even changing your activity or being engaged in a conversation can improve alertness, Rosekind says. But as soon as you stop the activity or conversation, you’re likely to feel sleepy again, he says.
After a night without sleep, your working memory is impaired. That means you can’t keep as many things in your mind at one time, Drummond says.
A study of 40 young adults who had 42 hours of sleep deprivation -- equivalent to staying up all night and the next day until a late bedtime -- showed a 38% decrease in working memory capacity. Imaging studies confirmed that the part of the brain involved in integrating information isn’t as active in people who are sleep deprived.