>> Body Struggles When Sleeping Time Changes

The human body has difficulty adjusting to different sleep times than previously thought, says a researcher studying sleep for NASA.

The space agency has been advising astronauts to begin going to bed two hours later than normal over a period of time to prepare for their desired sleep schedule, according to Timothy Monk, a University of Pittsburgh Medical Center psychiatry professor who is leading a study to find the best way to shift sleep cycles. That may not be the best approach, however.

"There's no doubt that changing your biological clock is difficult," says Monks. "What we're trying to do here is basically address the question of how you cope with something that is difficult."

Earth has 24-hour day-night cycle; space has a 90-minute day-night cycle. Monk also said, In space, the lack of day-and-night cues throws off the human brain's alarm clock and the body's natural rhythms go out of sync after three months.

"Space is a very unforgiving environment," he said. "If they scheduled sleep for the wrong time, an astronaut could end up having disrupted and un-refreshing sleep, leaving them feeling tired and irritable, and perhaps more apt to make mistakes."

Subjects in the first part of the study shifted sleep in two-hour blocks, but had poor sleep quality and were less alert.

Researchers found the body only adjusts itself by about one hour a night - not the two of NASA's current practices. The findings were published in this month's issue of Aviation, Space and Environmental Medicine.

A second phase of the study shifted sleep in 30-minute blocks; the final phase, just starting, will shift sleep in one abrupt movement.

"There is always some cost to performing tasks when we expect to be asleep, but by the end of the series of experiments" researchers should be able to advise NASA which approach is best, Monk said. Testing could last a couple of years, he said.

Monk said the study has implications for anyone who must change schedules - like shift workers and travelers.

"Many of us find that we have to change our sleep schedule, perhaps to accommodate work or school start times, or a change in our commute time," Monk said. "We often wonder if we should make the change all at once, or more gradually over several days or weeks. This research has the eventual aim of helping us make that decision in the best way possible."

In the meantime, Monk has some tips for people whose work schedules interfere with normal sleep patterns: Go to bed as soon as possible after a night shift; make rooms as dark and quiet as possible while sleeping; use caffeine sensibly, and avoid using alcohol before sleep. The jury is still out on whether melatonin helps, he said.