You know you've done it — stayed up too late and relied on coffee to get through the next day — but new research suggests that caffeine can only do so much.
That cup or cups of coffee may keep you awake the following day, but your performance is likely to be subpar, especially when it comes to more challenging tasks.
"Caffeine will likely improve your mood and alertness and may help you to attend to simple tasks, however, it will do little to improve more complex tasks," said study author Kimberly Fenn, an associate professor of cognition and cognitive neuroscience at Michigan State University's Sleep and Learning Lab.
"Caffeine simply cannot replace a night of sleep, and it is critical that individuals prioritize sleep and if they must endure a night without sleep, that they take the necessary precautions and avoid driving a car or performing any high-stakes tasks," Fenn said.
To get a better idea of what caffeine can, or can't, do in the face of sleep loss, researchers asked more than 275 people to complete a simple attention task as well as a more challenging one that required them to complete tasks in a specific order without skipping or repeating steps. The latter is known as a place-keeping task.
Folks either stayed awake overnight in the lab or slept at home. In the morning, all participants consumed a capsule that contained either 200 milligrams (mg) of caffeine or placebo and completed both tasks again. (An 8-ounce cup of regular coffee may contain 75 to 120 mg of caffeine.)
Sleep loss impaired performance on both tasks. Caffeine helped people successfully achieve the easier task, but not the more difficult one, the study found.
"If you are sleep-deprived, using caffeine will only help you with reaction time, not with being able to remember the steps you need to do in a procedure, "said Michael Breus, a sleep medicine expert and clinical psychologist in Los Angeles. He has no ties to the new study.
The findings were published recently in the Journal of Experimental Psychology: Learning, Memory, and Cognition.
Other experts not part of the research were quick to point out that sleep loss is dangerous, especially in the long run.
"People wear sleep loss like a badge of courage and say things like 'sleep is a poor substitute for caffeine,' but this is not true and can be dangerous," said sleep medicine expert Dr. Raj Dasgupta, an assistant professor of clinical medicine at the Keck School of Medicine at the University of Southern California, and a spokesperson for American Academy of Sleep Medicine.
"Pulling an all-nighter is the worst possible thing you can do to succeed on a test," said Dasgupta. "You need good-quality, deep restorative sleep if you are taking a test or performing a complicated task at work."
The new study just looked at how caffeine counters one night of sleep deprivation, but sleep loss is often chronic, stressed Thomas Roth, director of the Sleep Disorders and Research Center at Henry Ford Health System in Detroit.
"If you sleep five hours a night, you accumulate sleep debt, so even if coffee helps you on the first day, it will help you less on the fifth day as you accumulate even more sleep debt," he explained.
You will also develop a tolerance for coffee and need more and more to feel awake, increasing your risks of side effects, said Dr. Camilo Ruiz, medical director at Sleep and Internal Medicine Specialists in Fort Lauderdale, Fla.
"Caffeine has been used as a temporary stimulant to improve attention over many years," said Ruiz. "However, its effects are short-lived and side effects such as [heart] palpitations, jitteriness and [increased urination], to name a few, can be worse than the lack of attention or sleepiness itself."