A recent study indicates that pink noise, often believed to aid sleep, may actually impair sleep quality. Pink noise is characterized by having all audible frequencies but with lower frequencies more pronounced, distinguishing it from white noise, which plays all frequencies at equal intensity. Sounds are categorized by color based on their noise spectrum, with pink noise likened to the sounds of rain or ocean waves. Research into its benefits for sleep and memory has shown mixed results.
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Conducted by researchers at the University of Pennsylvania, the study involved 25 healthy adults, primarily young women, over a seven-night sleep lab assessment. Participants, who did not have sleep disorders and were not habitual users of sound machines, were monitored under various conditions: with no noise, only environmental noise, only pink noise, a mixture of pink and environmental noise at different volumes, and environmental noise combined with earplugs. Environmental noise included sounds such as traffic and sonic booms, with participants kept in darkness from 11 p.m. to 7 a.m.
The findings, published in the journal Sleep, showed that environmental noise significantly disrupted Stage 3 sleep, which is the deepest phase, by reducing it by an average of 23.4 minutes. Pink noise also diminished the time spent in REM sleep by 18.6 minutes, a vital stage for mood regulation and cognitive focus. Dr. Mathias Basner, the study’s lead author and a professor of psychiatry at the University of Pennsylvania, noted that he did not anticipate pink noise would disrupt sleep to such an extent. Previous studies had hinted at REM sleep reduction but had not been extensively examined.
Before and after each night, the participants underwent physiological and cognitive evaluations to assess the effects of the various noise conditions. Basner warned that losing even small amounts of REM sleep can accumulate, potentially impacting overall health. While the study focused on adults, Basner expressed concern that the effects on infants and children could be more pronounced, stressing caution with noise machines for younger populations.
Although pink noise helped some participants manage external sounds, earplugs proved more effective for blocking noise. The researchers did note some limitations in the study, including a small sample size and the short duration of observation. It is possible that participants might adjust to pink noise over an extended period.
Dr. Rafael Pelayo, a clinical professor in the division of sleep medicine at Stanford University, cautioned that because the study took place in a lab setting, the results might not reflect home sleep conditions. He suggested that if a sound machine enhances sleep, it should be used at a lower volume and with a timer to prevent all-night exposure.