After a detailed study, Japanese researchers have found a novel way to help shift workers deal with the disruption in their sleep cycles: take a 3 1/2 hour nap at work.

The study, published in the current issue of the journal Sleep, concluded that naps during the night shift can help alleviate the fatigue that often afflicts people who must work rotating shifts.

Researchers at the Kyorin University School of Medicine in Tokyo and at the University of Tokushima School of Medicine in Tokushima studied the sleep patterns of 16 male security guards who worked alternating 12-hour day and night shifts.

For example, the guards worked from 10 p.m. to 10 a.m. then had a day off. Next, they worked a day shift from 10 a.m. to 10 p.m. followed by another day off, and then went back to a night shift.

By working day and night shifts during the same week, the guards altered their natural sleep patterns, the researchers found. On their nights off, they generally slept eight hours. But when they worked nights and had to sleep during the day, they slept only four hours and moved more frequently between the lighter and deeper stages of sleep.

Older workers -- those in their fifties -- seemed to have the most trouble adjusting.

More than a quarter of working men and some 16 percent of working women in the United States rotate shifts according to the National Center for Health Statistics.