PERSONAL HEALTH : Guidelines to Sleep By

Those who work the night shift or erratic schedules tend to toss and turn at bedtime. Traffic, barking dogs and family members who can’t tiptoe can all thwart a good day’s sleep.

For many years, researchers have known that sleepiness varies greatly at different times of the day and that it is easier to sleep when body temperature is lower. Now, a team of Swedish researchers has found that the interval between sleep sessions interacts with body temperature to affect sleep quality.

After asking eight women in a laboratory to sleep and wake at various times over a 13-day period, the researchers offer this advice for those who must sleep at odd hours:

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* Stay awake for at least 12 hours (ideally longer) between sleep periods.

* If possible, sleep between 9 a.m. and 3 p.m., when body temperature is lower. Women got the most sleep, nearly six hours, when they followed this schedule, says Torbjorn Akerstedt, the Stockholm researcher who led the study, published recently in the journal Sleep.

* Avoid sleeping during the late afternoon and early evening, when body temperature is often highest.

The study makes perfect sense, says Michael M. Stevenson, clinical director of the North Valley Sleep Disorders Center in Mission Hills, who offers an additional suggestion:

“If you must change work schedules, move shifts forward if possible.” Going from a 9-to-5 shift to a 4-to-midnight one, for instance, is easier on the body than the reverse.