Objective  The effect of a small amount of alcohol on the sleep structure in relation to alcohol sensitivity was examined using polysomnography (PSG).
  Methods  Alcohol sensitivity was evaluated using alcohol patch test for all subjects. PSGs were performed on three nights after one night for acclimation, and subjects consumed no alcohol, 0.28 or 0.69 g ethanol/kg body weight, respectively, before going to bed. The percentages of sleep time in each sleep stage of 1, 2, 3+4 and rapid eye movement (REM), REM latency, and REM cycle were calculated.
  Subjects  Thirteen healthy female students (age 21.1±0.7 years) were enrolled in this study.
  Results  In all subjects, there were no significant differences in any of the sleep parameters between baseline night and alcohol nights. Six of the 13 subjects were sensitive to alcohol, in whom %stage REM was significantly decreased by alcohol consumption (baseline night: 18.3±6.2%, alcohol night I: 9.8±5.1% and alcohol night II: 11.0±2.8%), and the REM latency was significantly prolonged. The standard deviation of REM cycle was significantly greater on alcohol nights I and II than baseline night. There were no significant differences in other sleep parameters. In the other seven subjects who were insensitive to alcohol, none of the sleep parameters were significantly affected by alcohol consumption.
  Conclusion  REM sleep was adversely affected by a small amount of alcohol in alcohol-sensitive healthy young women. Alcohol sensitivity might play some important role in impaired REM sleep by an ingestion of a small amount of alcohol.