Different criteria of sleep latency and the effect of melatonin on sleep consolidation

Since there is no consensus definition of sleep onset, we studied different aspects of initial sleep periods in healthy volunteers taking melatonin. Two criteria for sleep latency were used: 10 minutes of uninterrupted sleep and 1.5 minutes of stage 1 sleep.

Forty healthy male volunteers (mean age 28 +/- 5 years) were assigned to 2 groups: 30 ingested melatonin and 10 placebo.

All volunteers underwent an initial polysomnogram (baseline) after a 1-night adaptation period. The next day, the placebo or a 10-mg dose of melatonin was administered for 28 days, 1 hour before sleep time, in double-blind fashion. The second polysomnogram was recorded on day 14.

Sleep laboratory

Chronic melatonin administration led to a significant reduction in sleep latency, using only the criterion 10 minutes of uninterrupted sleep. This effect suggests that melatonin may have a hypnotic effect, and the use of melatonin may lead to better sleep consolidation.

These results show differences that have clinical implications, since the criteria used to diagnose initial insomnia were based on sleep onset.