Studies of melatonin supplements have shown mixed results. The new report, published in the journal Sleep, shows that taking melatonin 30 minutes before bedtime improved sleep efficiency -- but only when people's bodies weren't making melatonin at the time.
James Wyatt, PhD, and colleagues conducted the study while Wyatt worked at Harvard Medical School and Boston's Brigham and Women's Hospital. Wyatt is now on staff at Rush University Medical Center in Chicago.
From Outer Space to the Bedroom
The study was partly designed to simulate shifting sleep schedules in astronauts on NASA's space shuttle. But the results may also have meaning here on Earth.
The findings may apply to jet lag, night-shift workers, and people with advanced or delayed sleep phase syndrome, write Wyatt and colleagues.
The study included 36 healthy young adults aged 18-30 who didn't have sleeping problems. The researchers gave participants a to-do list before the study started:
- Avoid alcohol, caffeine, nicotine, illegal drugs, and prescription medicines for three weeks.
- Stick to a regular sleep schedule for at least two weeks.
- Report daily bedtime and wake times to a laboratory voicemail.
After following those rules, participants reported to a sleep lab at Brigham and Women's Hospital.
Time Clues Concealed
At the sleep lab, participants stayed in dimly lit rooms with no clocks, calendars, or other cues about night and day.
For their first three days at the lab, participants were kept awake for 16 hours and allowed to sleep for eight hours.
Next, the researchers shifted participants to a 20-hour cycle. They kept participants awake for 13 hours and 20 minutes of each cycle. Participants were to sleep during the remaining six hours and 40 minutes of each cycle.
Participants followed that 20-hour cycle 24 times. During those cycles, they took melatonin or an identical pill lacking melatonin (placebo) 30 minutes before sleeping.
Afterward, participants got eight hours of sleep every 24 hours for three days.