We've long known that sleep-deprived workers can be a hazard to themselves and to productive work days. Many nodding off at the job consistently reach for a popular solution -- a cup of coffee, or perhaps an energy drink.
A group of researchers in the U.K. decided to put the caffeine solution to the test and see whether it actually helps workers perform better.
It does. A large review of 13 randomized, controlled studies in the U.K. showed that caffeine consistently improved memory, attention and performance.
Caffeine was even more effective than a nap in helping people's concentration.
"We've always understood that caffeine was beneficial, but this is the first systematic review of the evidence," said Phil Edwards, a co-author of the review, published Tuesday in The Cochrane Library.
"We're interested in reducing injuries in people who have to work in the night shift," said Edwards, a senior lecturer in statistics at the London school of Hygiene and Tropical Medicine.
"We thought the use of sleep to alleviate the effects of tiredness would be what would have the most beneficial effect," he said.
Sleep experts debate whether some of our favorite quick fixes for sleep loss really help us concentrate on a daily basis. They say in some cases, what helps in the short term might hurt our concentration in the long term.
Edwards said many of the studies only followed the concentration of workers in the few hours after the jolt of caffeine. They did not follow the workers to see how they did once the caffeine was out of their system.
"That's somewhere on the range of three to five hours depending on the individual," said Dr. Donna Arand, clinical director of the Kettering Sleep Disorder Center in Dayton, Ohio.
How much caffeine, an individual's metabolism and the amount of food you ate with the caffeine can also affect the length of time it keeps you going.
Arand said studies have proven the benefits of caffeine more conclusively than any problems it causes with sleep afterwards.
"If somebody's drinking caffeine during the night shift... that's been shown to improve their performance and reduce accidents," she said. "Really, the studies have been inconsistent saying that they've been affecting sleep at all."
Arand added, "The one thing that caffeine does affect is the time it takes you to fall asleep."
But Dr. Meir Kryger of the National Sleep Foundation said he often sees people who've fallen into a sleepless cycle because of caffeine overuse. The person doesn't get enough sleep one night and so drinks caffeine during the day to get through. At bedtime the caffeine still keeps them awake, so the cycle continues.
"We see this all the time in the sleep clinic," said Kryger, director of research and education at Gaylord sleep medicine in North Haven, Connecticut.
"We know caffeine will keep you awake and alert. However, it's a two-edged sword," he said.
Here are other ways people try to help their sleep-wake cycle, beginning with alcohol -- which, sleep experts say, usually does more harm than good.
"You will fall asleep quicker with alcohol, but when the alcohol level drops, it actually wakes your brain up," said Kryger. "If someone snores, or if someone has a disease called sleep apnea, it will make things substantially worse."