NIGHT-shift workers who must remain alert when their bodies are at their lowest ebb would benefit from a four- hour nap the evening before the shift begins - plus strong coffee on the job, say American researchers.

A team from Wright State University, Dayton, Ohio, gave psychological tests to men aged 18-30, at regular intervals during a 24-hour period starting at 8pm. Some had a four-hour nap just before work and were given caffeine 'top-up' tablets at 1.30am and 7.30am. The others had four one-hour naps during the night and placebo tablets. The men who had four-hour naps were significantly more alert, performing better in logical reasoning and addition tests.

According to a report in New Scientist, the early evening nap prepares the body for sleep deprivation, while the caffeine probably helps to reverse the normal circadian decline in alertness.