The diverse sleep structure of mid-day nap in college students

The aim of this study was to investigate the sleep structure of mid-day naps in students who frequently nap, and to determine whether this structure has any impact on their subjective feelings after nap. A total of 91 college students (male, mean age 20.47 ± 2.02 years) completed one-hour mid-day nap with polysomnographic recording in a sleep laboratory. Upon awakening, self-ratings of sleep quality and sleepiness were assessed using questionnaires. The sleep structure of mid-day naps varied among participants: 47.3% participants experienced stage-1, -2, and -3 non-rapid eye movement (NREM) sleep in sequence in the one-hour nap, while rapid eye movement (REM) sleep occurred between 40 and 60 min after lights off in 27.5% participants, and less than 15 min in 16.5% participants. After nap, participants who achieved stage-3 sleep reported better sleep quality, but the subjective sleepiness was not influenced by the sleep stage contained in nap or the sleep stage at awakening. These findings highlight the diversity in the sleep structure of mid-day naps, suggesting that this variability may need to be considered when studying the effects of napping.