Pink Noise May Reduce Restorative REM Sleep, Earplugs More Effective Against Noise

A new study published in the journal Sleep by the University of Pennsylvania Perelman School of Medicine indicates that pink noise, often used for sleep promotion, may reduce restorative REM sleep. The research also found that earplugs demonstrated greater effectiveness in protecting sleep against traffic noise compared to pink noise.

The findings from the study may challenge the common use of ambient sound machines and applications marketed as sleep aids.

Dr. Mathias Basner, MD, PhD, a professor of Sleep and Chronobiology in Psychiatry and the study's lead author, noted that REM sleep is important for memory consolidation, emotional regulation, and brain development.

The study's results suggest that playing broadband noise during sleep could have implications, particularly for children, whose brains are still developing and who spend more time in REM sleep than adults.

Study Methodology

Researchers observed 25 healthy adults, aged 21 to 41, in a sleep laboratory over seven consecutive nights, providing eight-hour sleep opportunities. Participants reported no prior use of noise as a sleep aid or any existing sleep disorders.

Subjects slept under various controlled conditions, including:

• Exposure to aircraft noise
• Exposure to pink noise
• Exposure to aircraft noise combined with pink noise
• Exposure to aircraft noise with earplugs

Each morning, participants completed tests and surveys designed to assess sleep quality, alertness, and other health effects.

Understanding Sleep Stages and Pink Noise

During sleep, individuals cycle through periods of deep sleep and REM (Rapid Eye Movement) sleep.

• Deep Sleep (N3 Stage): Important for physical restoration, memory consolidation, and the clearance of brain toxins.
• REM Sleep (Dream Sleep): Contributes to emotional regulation, motor skills, and brain development. Both stages are complementary and considered crucial for restorative sleep.

Pink noise is a type of broadband noise, characterized as a continuous sound distributed across a broad frequency range, often described as static-like. Broadband noise encompasses white noise and other noise colors, such as brown and blue noise, which vary in their energy content across the audible spectrum, influencing their perceived pitch. Natural sounds, like ocean waves or rainfall, as well as household appliances, such as air conditioning units and fans, also produce broadband sounds.

Key Findings

The study yielded several key findings regarding sleep duration and quality under different noise conditions:

• Aircraft Noise: Exposure to aircraft noise alone was associated with approximately 23 fewer minutes per night spent in N3, the deepest sleep stage, when compared to no noise. Earplugs largely mitigated this reduction in deep sleep.
• Pink Noise Alone: Pink noise alone, at 50 decibels (a level comparable to moderate rainfall), was associated with a nearly 19-minute decrease in REM sleep.
• Combined Noise: When pink noise was combined with aircraft noise, both deep sleep and REM sleep durations were significantly shorter compared to noise-free control nights. Additionally, time spent awake increased by 15 minutes, an effect not observed during nights with only aircraft noise or only pink noise.
• Subjective Sleep Quality: Participants reported lighter sleep, more frequent awakenings, and poorer overall sleep quality when exposed to aircraft noise or pink noise, unless earplugs were used.

Implications for Sleep Habits

The study's results suggest that earplugs, which are used by a significant percentage of Americans for sleep, are effective. Conversely, the overall health effects of pink noise and other types of broadband noise marketed as sleep aids require more comprehensive study. Millions of people utilize broadband noise during sleep nightly through various platforms, including streaming services like Spotify and YouTube; however, research on the effects of broadband noise on sleep remains limited and inconclusive.

Disruption of REM sleep is a characteristic associated with conditions such as depression, anxiety, and Parkinson's disease. Dr. Basner highlighted that young children, who spend considerably more time in REM sleep than adults, may be particularly susceptible to potential negative effects of pink noise. He noted that it is a common practice for parents to place sound machines near newborns or toddlers with the intention of aiding sleep.

"Overall, our results caution against the use of broadband noise, especially for newborns and toddlers, and indicate that we need more research in vulnerable populations, on long-term use, on the different colors of broadband noise, and on safe broadband noise levels in relation to sleep."

Funding

This research received funding from the U.S. Federal Aviation Administration Office of Environment and Energy through ASCENT, the FAA Center of Excellence for Alternative Jet Fuels and the Environment. Specific funding details include project 86 through FAA Award Number 13-C-AJFE-UPENN, conducted under the supervision of Susumu Shirayama. A disclaimer stated that the opinions, findings, conclusions, or recommendations expressed in this material are those of the investigators and do not necessarily reflect the views of the FAA.