Napping and cognitive performance during night shifts: a systematic review and meta-analysis

Study Objectives: To examine the benefits of napping during night shifts on cognitive performance. Methods: Medline, Cochrane Library, Science direct, and Embase databases were searched up to July 1, 2019. Cognitive performance during night shifts, both before and following napping or under control conditions (no nap), in working-aged adults, were analyzed by time and by type of cognitive function (executive function, attention, instrumental function, and memory). Estimates were pooled using random-effects meta-analysis. Results: A total of 18 articles (6 in real-work and 12 in laboratory) with a total of 494 participants were included. The mean nap duration was 41.6 +/- 28.3 min, occurring between 12.00 am and 4.10 am, with a mean time set at 2.12 am. Cognitive performance did not differ at baseline between the groups (effect size 0.02, 95% CI -0.09 to 0.13). There was an overall improvement in performance following a nap compared to the control condition without a nap (0.25, 0.10 to 0.41). Positioning naps early in the night and activity (simulated work tasks) tended to improve cognitive performance (-0.57, -1.16 to 0.002, and 0.082, -0.04 to 0.33, respectively). The improvements were primarily seen 30 min after awakening. Only memory deteriorated immediately after awakening without an overall change in global cognitive performance. Conclusion: Napping during night shifts seems to improve cognitive performance. Napping early in the night and activity may benefit cognitive performance over time. Considering lack of data in real work environments, further studies are warranted before preconizing napping during night shifts as a preventive strategy (safety, health, and economic outcomes).