Caffeine can help those who work shifts or nights to make fewer mistakes, say Cochrane researchers at the London School of Tropical Medicine, who reviewed data from 13 trials that studied the effects of caffeine on performance.

Most trial participants were between the ages of 20 and 30. They took caffeine in a variety of forms — coffee, pills, energy drinks, or caffeinated foods. Performance was judged by driving or by neuropsychological tests. Caffeine appeared to reduce errors, compared to naps or placebos, and improve performance on tests that concentrated on memory, attention, reasoning, concept formation, and perception.

The findings could be very important for health workers and others who work shifts, including truckers. In fact, more than 15 percent of workers in industrialized nations do nighttime or shift work. Their natural body clocks — circadian rhythm — may be upset, and result in drowsiness during working hours. Sleepiness increases the risk of a host of problems including traffic crashes, medical errors, and occupational injuries.

"It seems reasonable to assume that reduced errors are associated with fewer injuries, although we cannot quantify such a reduction," says lead researcher Katharine Ker.

Since the degree of disruption to natural body clocks varies with age, the researchers noted that research needs to be done on how caffeine affects older workers.

In the United States, about 90 percent of people consume some type of caffeine daily. According to the Mayo Clinic, two to four cups of coffee daily — the way many Americans get their daily dose — aren't harmful.