Systematic review: auditory stimulation and sleep

Study Objectives: Auditory stimulation devices (white and pink noise) are used to mask sounds and facilitate relaxation and sleep; however, the effectiveness of this intervention is not well established. This systematic review examined the scientific literature for the effect of specific types of auditory stimulation on sleep outcomes in adults. Methods: The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement guided this review. Searches were conducted in 9 databases for intervention studies that could easily be employed in clinical practice. We excluded other types of auditory stimulation (music alone, binaural tones, and synchronization). Two reviewers screened abstracts and full-text articles for eligibility, with conflicts resolved by a third reviewer, and extracted data. Risk of bias was assessed with the Effective Public Health Practice Project Quality Assessment Tool for Quantitative Studies. Results: Thirty-four studies reported results of 1,103 persons participating in 3 categories of interventions: white noise (18), pink noise (11), and 6 multiaudio (some combination of white, pink, music, or silence). Nineteen studies had positive findings in terms of improving sleep outcomes: 6 white noise (33%), 9 pink noise (81.9%), and 4 multiaudio (66.7%). Multiaudio had the lowest (better) risk of bias (mean/standard deviation: 1.67/0.82) compared to white (2.38/0.69) and pink noise (2.36/0.81). Conclusions: Although there was no strong evidence to support use of auditory stimulation, none of the studies reported any adverse effects with short-term application of auditory stimulation during sleep. Future research needs to include confounding factors that can affect outcomes, including one's noise sensitivity, personality, and other conditions or medications that may affect sleep.