The effect of meditation training on sleep: A systematic review of polysomnographic studies

Introduction: Numerous clinical studies have reported improvements in subjective sleep quality and reduction in insomnia severity following participation in mindfulness-based interventions (MBIs). Conversely, studies examining the sleep-wake patterns of long-term meditators (LTM) across various meditative traditions have indicated a subjective decrease in sleep duration and an increase in awareness during sleep. Recently, there has been a rise in polysomnographic studies investigating the impact of meditation on objective sleep parameters, both in clinical and non-clinical samples. Therefore, it would be helpful to integrate and review these new findings in order to understand and explain this apparent contrast in the literature. This review aims to investigate the effects of meditation on the macro and microstructure of sleep in individuals with or without sleep disorders. Method: A systematic literature search was conducted in PubMed, Web of Science, Scopus, PsycINFO, and CINHAL following the PRISMA guidelines. The quality of the retrieved documents was evaluated using the Kmet Checklist Appraisal Tool. Results: Thirty-one studies were included in the qualitative synthesis, with the majority investigating variables of sleep macrostructure. Regarding the macrostructure of sleep, findings varied depending on the population studied and the types of meditation practiced. Some studies reported an increase in arousal and a reduction in total sleep time, while others found no change in objective sleep parameters. Cross-sectional studies comparing LTM to novices reported an increase in N3 and REM sleep in meditators. Concerning the microstructure of sleep, one clinical study reported an increase in NREM beta power after an MBI, while studies investigating LTM reported an increase in prefrontal and left parietal theta-alpha and gamma activity in NREM. Conclusion: Overall, these findings suggest that meditators may be more susceptible to experiencing a reduction in sleep duration due to heightened awareness and arousal during sleep. However, it is important to interpret these results cautiously, as there is a substantial heterogeneity in the included studies which influenced the investigated outcomes. Moreover, a very limited number of studies investigated the microstructure of sleep. Given these findings, we propose to develop a unified research framework for future studies to facilitate comparisons of results across different meditation techniques and study populations.