Trait Inter-Individual Differences in Deep Sleep

Primary author: Julie Erwin

Primary college/unit: Elson S. Floyd College of Medicine
Campus: Spokane


Inter-individual differences in the amount of deep sleep, stage N3, in nighttime sleep have been found to be large and trait-like, even during recovery sleep after sleep deprivation. We investigated whether this phenomenon extends to daytime sleep, and whether it is robust to prior caffeine intake.

In an 18-day in-laboratory study, 12 healthy adults underwent three 48-hour periods of total sleep deprivation. In randomized, counterbalanced, double-blind fashion, participants received either placebo, 200 mg caffeine, or 300 mg caffeine every 12 hours during sleep deprivation. Each sleep deprivation period was preceded by three baseline sleep periods (21:00-07:00) and followed by a daytime recovery nap (07:00-12:00). Sleep periods were recorded polysomnographically. Analyses focused on the baseline night immediately preceding and the daytime recovery nap immediately following each sleep deprivation period.

Daytime recovery naps had 44.6±5.1 minutes (mean±SE) more stage N3 sleep than baseline sleep periods (p<0.001). Daytime naps preceded by 200 or 300 mg caffeine intake every 12 hours during sleep deprivation had 15.4±6.2 and 21.6±6.2 minutes less stage N3 sleep, respectively, than daytime naps in the placebo condition (p=0.003). Across the baseline nights and daytime naps, regardless of caffeine condition, there were large inter-individual differences in stage N3 sleep, with a standard deviation over individuals of 23.2 minutes and considerable stability (intraclass correlation coefficient: 0.70). Thus, the amount of deep sleep is a trait characteristic that is robust to sleep deprivation, time of day, and caffeine.