Pink Noise Disrupts Sleep Instead of Enhancing It – Integrative Practitioner

Written by Erin Yeh

Pink noise, a type of broadband noise that sounds uniform and constant, is often promoted as a tool for getting a restful night’s sleep. However, a recent study published in He sleeps (DOI: 10.1093/sleep/zsag001) suggests that pink noise may have the opposite effect. Specifically, pink noise may negatively impact REM sleep, potentially leading to long-term neurological damage.

How does noise affect sleep?

To determine the effect of pink noise on sleep quality, a team of researchers from the University of Pennsylvania Perelman School of Medicine enrolled 25 participants in a randomized study. Participants ranged in age from 21 to 41 years and were divided into seven groups, each with up to four members. The study was conducted over seven nights in a sleep laboratory. Each morning, participants filled out questionnaires, took cognitive tests, and received cardiovascular measurements before going about their normal daily activities and returning to the laboratory in the evening. Participants were also instructed not to nap, exercise, or drink alcohol during the day, and also not to consume caffeine after 3:00 p.m.

There were six conditions to which the groups were exposed each night: control night without exposure to any noise; Environmental noise Pink noise at 50 dB; Environmental noise plus pink noise at 40 dB; Environmental noise plus pink noise at 50 dB; Environmental participants wear earplugs. The groups experienced each condition on different nights, but neither participants nor study staff were informed of the sequence of noise conditions.

The results showed that environmental noise only reduced slow-wave sleep and overall sleep depth, as well as increased EEG arousal, suggesting increased sleep fragmentation. These findings are consistent with previous studies on traffic noise affecting sleep.

However, perhaps the most notable finding is the effect of pink noise on sleep. Pink noise at 50 dB did not increase sleep fragmentation or reduce sleep depth, but it did reduce REM sleep. The team speculates that pink noise may activate auditory pathways that inhibit neurons in the midbrain and hypothalamus, which play an important role in initiating and maintaining REM sleep. As such, pink noise may make REM sleep more vulnerable when intermittent noise is present and delay the return of REM sleep even after the noise stops.

The combination of environmental noise and pink noise resulted in poor sleep quality. Nights with environmental noise and pink noise showed deeper sleep and REM sleep, shorter total sleep time, lower sleep efficiency, and longer wake time. Subjective assessments indicated poor sleep quality, wakefulness, and mood, although no worse than environmental noise alone.

However, pink noise has shown some short-term benefits. When playing with environmental noise, it reduces wake durations, brief wake EEGs, and overall sleep fragility with a dose-dependent reduction. However, these benefits were partially offset by increased sleep fragmentation during quiet periods.

Earplugs have been found to be most effective. Wearing earplugs restored approximately 17 to 23 minutes of deep sleep that had been lost to environmental noise, representing an approximately 72% reduction. Sleep structure, sleep quality, mood, and alertness did not differ with earplugs than on noise-free nights. Previous studies have reported mixed results about the comfort of earplugs and desirability of using them, but in this study, participants generally found the earplugs comfortable and felt they slept better while wearing them. More research will be needed to determine whether custom-made or higher-quality earplugs can increase noise reduction and comfort.

Limitations of the study

The study had a few limitations. The researchers initially recruited 27 participants. Two subjects withdrew on the second and third nights, respectively, and were not included in the data analysis. Another participant withdrew on the fifth night but was included in the data analysis. This may have an understandable impact on the results of the data analysis, especially since the sample size is very small. Furthermore, most participants were young and healthy, so the results of this study may not apply to younger, older, or unhealthy populations. Additionally, there were some nights when the noise systems would malfunction. For example, Group 3 experienced a system malfunction in three out of four subjects during the second night, resulting in the research team having to replace the sixth night with another control night.

The duration of REM sleep increased during the study period. Since three of the six conditions included pink noise and pink noise reduces REM sleep, this increase may reflect a buildup of REM sleep pressure caused by selective REM sleep deprivation. In a different study of male college students, results indicated recovery of REM sleep after three nights of white noise exposure to 93 dB A-weighted, suggesting REM sleep deprivation during exposure. However, the current study design cannot distinguish between REM sleep deprivation and pink noise habituation. More studies are needed to clarify these effects.

A major limitation of this study is the wide variation in sound exposure, including differences in noise type and sound pressure level for both EN events and broadband noise. EN events were also triggered at LAS, with maximum levels of 45, 55, and 65 dB, but it is unclear how these results apply to lower sound levels. Other broadband noises (such as white, blue, or brown) vary in their acoustic energy across the audible spectrum, and it is not possible to test all combinations. An important step for long-term field studies is to determine the optimal noise color and level that best attenuates the sleep disturbance associated with EN while providing maximum protection at the lowest possible sound level.

The critical role of REM sleep

Although the roles of REM sleep are still not fully understood, it is known to support memory, brain plasticity, and emotional regulation. Lack of REM sleep has been linked to mental illnesses, such as depression, PTSD, and anxiety. In addition, REM sleep behavior disorder is usually a prodromal biomarker of Parkinson’s disease and dementia with Lewy bodies, possibly due to impaired clearance of brain waste.

REM sleep is particularly important for brain growth and cortical maturation during the early stages of development. While there is little evidence on the effects of broadband noise on a child’s brain development, the results of this study suggest that this noise can cause more harm than good. The common practice of using broadband noise machines in the bedrooms of newborns and toddlers may seem to improve sleep by naturally reducing their fragmented sleep, but this perceived benefit may disrupt the rapid eye movement (REM) sleep that is critical for their neurodevelopment. More research needs to be done to fully understand the effects of broadband noise on early brain development in infants and children.