24 Hours Not Enough? See the Light

Pulses of Bright Light May Reset Body Clock and Stretch the Day to 25 Hours

Medically Reviewed by Louise Chang, MD on May 14, 2007
From the WebMD Archives

May 14, 2007 -- Get ready for the 25-hour day. A new study, funded by NASA, shows that it's possible to cram an extra hour into the day.

The researchers included Charles Czeisler, MD, PhD, director of the sleep medicine division at Harvard Medical School and chief of the sleep medicine division at Boston's Brigham and Women's Hospital.

They studied 12 healthy young adults (average age: 28) who volunteered to spend 65 days living in individual rooms without windows, clocks, or any other time cues.

Before the experiment began, the volunteers got eight hours of nightly sleep at home for at least three weeks.

When they reported to the lab, they spent three days on a normal 24-hour day. Then the researchers tweaked the hours of light and darkness to pinpoint the participants' natural circadian rhythm, commonly called the "body clock."

Next, the scientists tacked on an extra hour of light to each participants' natural amount of daily wakefulness.

The researchers didn't just leave the lights on for an extra hour. At the end of each "day," the scientists cranked up the light in the overhead fluorescent lights, delivering two pulses of extremely bright light.

The bright light pulses were nearly 10 times brighter than normal room light, according to the study.

After the pulses of bright light, participants didn't go to sleep right away. They stayed up an extra hour, effectively getting 25 hours per day.

Participants stayed on the 25-hour-day cycle for a month. They adjusted to the schedule, judging by their core body temperature and levels of melatonin, a hormone involved in circadian rhythms.

Before leaving the lab, participants spent three days on a normal 24-hour schedule.

The findings may come in handy if astronauts go to Mars. A Martian day lasts for 24.65 earthly hours, note the researchers. They argue that without resetting the body clock to a 25-hour day, astronauts on Mars would be constantly jetlagged, which could be dangerous.

Of course, Mars-bound astronauts aren't the only people with circadian rhythm issues. Shift workers and people with sleep disorders may also have body clock problems.

The researchers write that "the implications of these findings are important, because they could be used to treat circadian misalignment associated with space flight, shift work, and circadian rhythm sleep disorders."

The study appears online in the early edition of Proceedings of the National Academy of Sciences.

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Show Sources

SOURCE: Gronfier, C. Proceedings of the National Academy of Sciences, week of May 14-18, 2007; online early edition.

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