Systematic Review Cautions Promoting White Noise Machines as a Viable Sleep Aid

Despite widespread use of white noise machines to promote sleep, a new analysis published in Sleep Medicine Reviews indicates that current evidence for the ability of continuous noise to improve sleep was of very low quality, and that further assessment of the potential benefits and harms of white noise machines is needed.

These findings emerged from a systematic review of 38 studies, in which the primary outcomes had been defined as latency of sleep onset, quality of sleep, fragmentation of sleep, and duration of sleep and wake periods. Ultimately, the authors of the review found significant heterogeneity in methodologies used to measure sleep, characteristics of noise, intervention adherence, interventions or conditions for control groups, and occurrence of multiple experimental interventions simultaneously. They noted that future research must utilize objective measures of sleep and describe noise exposures in more detail before continuous noise can be promoted as a viable sleep aid.

Neurology Learning Network discussed these findings, their implications, and potential avenues of future research further with study author Mathias Basner, MD, PhD, professor in the Division of Sleep and Chronobiology in the Department of Psychiatry at the University of Pennsylvania School of Medicine in Philadelphia, Pennsylvania.

Neurology Learning Network: You and your colleagues noted that many have claimed that white noise could be a viable, nonpharmacological approach to fostering sleep and improving quality of sleep. Could you elaborate on that?

Dr Basner: What prompted this review was that white noise machines are advertised as ways to help people fall asleep quickly and to promote high-quality sleep. My team and I have been researching the effects of noise on sleep and how noise intruding into the bedroom can interfere with one’s sleep. The concept of fighting noise with noise seemed strange to us, which is why we wanted to examine the existing literature on this topic. We wanted to know whether there is a positive effect of introducing white noise into the bedroom to promote sleep, especially given the widespread use of white noise machines and apps.

I think the concept that white noise masks unwanted noise in the bedroom is sound in general. If you introduce a constant broadband sound, you are masking other events that are then not as easily perceived by the body with the hope that the degree of disturbance caused by these external noises decreases.

NLN: In your systematic review, you and your colleagues found that the evidence to support the use of continuous noise to improve sleep was of very low quality and ultimately contradicted its widespread use. Could you discuss this in more detail, and if this finding yet has a clinical impact in terms of recommendations for sleep?

Dr Basner: We identified 38 studies that have examined the effects of white noise of sleep, and all of them were very heterogeneous in terms of study populations, settings, the use of self-report data, etc. Selfreport report data is especially problematic when it comes to sleep because people who are asleep are not necessarily aware of their surroundings.

That said, there were a few studies that used objective measures, but not all of them met the gold standard of metrics. The results of these studies were also very heterogeneous—some positive findings, some negative findings, and many nonfindings. Some of that is also due to the fact that many studies were really small, with the majority of the studies conducted in no more than 10 people.

Using established criteria, we examined the evidence for these machines in their ability to actually promote sleep, and we found that this evidence was of very low quality. The data are simply not there to support this notion that white noise machines are working in the ways they are advertised to help promote sleep, but the data also do not necessarily indicate that these machines are not working either.

NLN: What areas of future research are still needed in this field?

Dr Basner:  I think we need to go back to the laboratory, enroll participants in a sleep study, instrument them with gold standard technology (polysomnography), and investigate how white noise affects their sleep in different noise scenarios. Granted, these would be only shortterm studies, and they would require continued follow-up in which people are exposed for a longer time to white noise during sleep in order to obtain some objective measurements for whether white noise machines truly promote sleep.

Another area for future research would be exploring the potential harms of using white noise machines to promote sleep. At least 1 study among the 38 reviews included in our analysis found that by introducing white noise into the bedroom, sleep fragmentation or sleep disturbance had increased among participants.

A third area of future research would involve the use of white noise to mask other environmental sounds. Some of the sounds that would be masked, such as a smoke alarm or a baby crying, actually may be meaningful. Another issue with many of the reviews included in our analysis was that the description of the noise (i.e., type of noise, noise level, etc.) in these reviews was very poor.

Finally, introducing a noise source into the bedroom may contribute to hearing loss, as the auditory system, like the brain, needs to wind down and get rid of waste products at some point. For all of these reasons, we need to conduct a controlled laboratory study that investigates these factors and reports all exposures accordingly.

NLN: What take-home message do you hope to leave with neurologists, neurology providers, and researchers?

Dr Basner: Our review indicates that we currently do not have enough knowledge to conclude whether white noise is an intervention that should be promoted for sleep or not. That said, there are definitely some self-report data available that indicate that people feel white noise helps them sleep. If patients are only using white noise to fall asleep, it may be worth suggesting to put the machine on a timer so that it turns off after half an hour or so, after the patient has fallen asleep and there is no potential for sleep to be disrupted afterwards.

It may also be worth suggesting to try to find the lowest white noise or sound level possible that still works for the patient. As long as we do not really know whether these white noise machines and apps truly work or whether they have potential detrimental effects, I would suggest erring on the side of caution and trying to bring down the volume to a minimal level that still works for patients.

Based on the data we found, I would not yet say that we should discourage white noise machines for sleep, but I do believe that we still need more information to support recommending it to patients to promote sleep.

—Christina Vogt

Reference:
Riedy SM, Smith MG, Rocha S, Basner M. Noise as a sleep aid: A systematic review. Sleep Med Rev. 2021;55:101385. doi:
10.1016/j.smrv.2020.101385