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.
Confusing Night and Day
Participants stayed at the sleep lab throughout the study. They wore special caps that monitored their brain activity and sleep. The researchers also checked participants' blood samples for melatonin levels.
The point was to force participants to sleep at odd hours and monitor melatonin's effects. The time shift was like flying four time zones eastward every day, according to a Rush University Medical Center news release.
The researchers focused on what they call participants' "sleep efficiency." Sleep efficiency was calculated by dividing total sleep time by scheduled time in bed.
When participants were making their own melatonin (as shown by the blood tests), the use of melatonin supplements didn't affect sleep efficiency. But sleep efficiency improved when participants took melatonin supplements while their bodies weren't making melatonin, the study shows.
However, sleep efficiency was best with melatonin made by the body, according to the results.
Hormone of Darkness
"Melatonin has been shown to be released primarily during the hours of darkness," the researchers write.
If their findings are right, that may mean that melatonin supplements help sleep efficiency most when taken before daytime sleep, when the body may not be making melatonin.
Since the study only included healthy people without sleep problems, it's not clear if the findings apply to other people.