Noise and Sleep Disruption: WHO Guidelines, EEG Arousal Thresholds, and Masking
WHO Night Noise Guidelines (2009) recommend <40 dB(A) Lnight to prevent sleep disruption; EEG arousals occur reliably at peaks above 35 dB(A) during NREM sleep and at lower thresholds in REM; chronic exposure >55 dB(A) increases cardiovascular disease risk significantly.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| WHO recommended night noise level | 40 | dB(A) Lnight | WHO 2009; annual average outside bedroom window; above 40 is adverse health territory |
| EEG arousal threshold during NREM sleep | 35–40 | dB(A) peak | Muzet 2007; single noise peaks; threshold lower in lighter sleep stages |
| EEG arousal threshold during REM sleep | 20–25 | dB(A) peak | REM is paradoxically more sensitive to meaningful sounds (name-calling, baby crying) |
| Traffic noise cardiovascular disease risk | Significant | association | Halonen et al. 2015; each 10 dB increase above 55 dB Lnight: 6% higher CVD risk |
| White noise sleep latency benefit | 38 | % reduction in sleep onset | Stanchina et al. 2005; white noise reduces arousal probability from noise spikes |
How Sound Disturbs Sleep
The sleeping brain does not fully disconnect from auditory input. Sound is processed hierarchically:
- Physical acoustic energy → cochlea → auditory nerve
- Thalamic gating: During NREM, thalamic reticular nucleus generates sleep spindles that partially block thalamocortical relay
- Primary auditory cortex: Still responds to sound during sleep (reduced amplitude)
- Arousal system: Locus coeruleus and reticular activating system can be recruited by loud or meaningful sounds
Sleep Stage Vulnerability
| Stage | Arousal threshold | Notes |
|---|---|---|
| N1 | Very low (~20 dB) | Lightest sleep; barely consolidated |
| N2 | Moderate (~35 dB) | Spindles provide partial protection |
| N3 | Highest (~45 dB) | Most resistant; spindles + slow oscillations |
| REM | Variable | Physically resistant to motor noise; semantically sensitive |
REM paradox: During REM sleep, people are harder to arouse with white noise but more sensitive to meaningful stimuli (own name, baby cry). This reflects higher-order cortical processing continuing during REM.
Health Consequences of Chronic Night Noise
Cardiovascular Pathway
Basner et al. (2014) synthesized the mechanistic chain: noise arousal → cortisol/catecholamine release → elevated blood pressure → endothelial dysfunction → atherosclerosis acceleration. Chronic rather than acute exposure drives population-level risk. Halonen et al. (2015) found each 10 dB increase in road traffic noise above 55 dB was associated with ~6% higher cardiovascular morbidity in a London cohort.
Sleep Architecture Effects
Muzet (2007) review: chronic noise exposure above WHO limits consistently reduces:
- SWS proportion (most vulnerable to fragmentation)
- Total sleep time (-20–40 min/night)
- Self-reported sleep quality
- Next-day cognitive performance and mood
Noise Mitigation Strategies
| Strategy | Effectiveness | Notes |
|---|---|---|
| Earplugs (NRR 25–33) | High | Reduces peak exposure by 15–25 dB; discomfort limits use |
| White/pink noise masking | Moderate | Best in variable-noise environments |
| Double-pane windows | High | 20–30 dB reduction for traffic noise |
| Heavy curtains/carpets | Low–moderate | 3–5 dB reduction |
| Room relocation | High | Face bedroom away from traffic sources |
Related Pages
Sources
- WHO — Night Noise Guidelines for Europe. WHO Regional Office for Europe (2009)
- Muzet A — Environmental noise, sleep and health. Sleep Med Rev (2007)
- Basner M et al. — Auditory and non-auditory effects of noise on health. Lancet (2014)
- Halonen JI et al. — Road traffic noise is associated with increased cardiovascular morbidity. Eur Heart J (2015)
Frequently Asked Questions
Does the brain fully tune out noise during deep sleep?
No. The sleeping brain continues to process sound throughout the night. During NREM sleep, the auditory cortex shows attenuated but present responses to stimuli. Sleep spindles — 12–15 Hz bursts during N2 — serve as an endogenous noise gate that reduces thalamocortical relay of external noise, helping maintain sleep. However, this protection is incomplete: EEG arousals from noise peaks above 35–40 dB occur even in N3, and during REM sleep, the brain may actually be more sensitive to semantically significant sounds (a sleeping parent responds to their baby's cry but not louder traffic). Habituation to chronic noise is behavioral, not physiological — arousals continue even when people report not noticing the noise.
Does white or pink noise actually help sleep?
Masking noise works by raising the ambient noise floor, reducing the contrast between background and noise spikes. A sudden 70 dB car horn against a 30 dB bedroom is more arousing than against a 50 dB white noise background. Studies show white noise reduces sleep-onset latency ~38% in noisy environments, and reduces nocturnal awakenings. Pink noise (weighted toward lower frequencies) shows additional EEG effects — enhanced slow-wave oscillations in some studies. However, effectiveness depends on the noise environment; in already-quiet rooms, adding noise is counterproductive. Fan noise (narrow frequency range) is less effective as a masker than broadband white/pink noise.