1. In this update to the World Health Organization (WHO) systematic review and meta-analysis, evening transport noises have a negative effect on sleep quality.

2. Additionally, pre-existing WHO recommendations on sound thresholds at night, including 45 dB for road traffic, 44 dB for rail traffic, and 40 dB for air traffic, remain adequate targets to prevent sleep disturbances.

Evidence Rating Level: 1 (Excellent)

Sleep is an important component to physical and mental health and well-being. Environmental noises have been linked to a significant burden of disease with regards to sleep. The World Health Organization (WHO) has published guidelines for protecting human health from exposure to environmental noise, including recommendations for target nighttime noise levels to mitigate the effects of traffic noise on sleep. However, these guidelines were based off a 2015 systematic review and meta-analysis and have not been updated since.

This systematic review and meta-analysis aimed to update the data and evidence behind these recommendations by including studies published up to 2021. Eligible studies include assessment of self-reported sleep disturbances. This study added 11 additional studies to the pre-existing 25 studies from the original systematic review. The study included only primary investigations in humans exposed to environmental noise from aircraft, road, and rail traffic at home, with sound pressure levels measured or predicted at the participant’s home. The study excluded those with subjective evaluations of noise levels and those that did not specify noise levels at the participant’s home address. The systematic review was prepared using the PRISMA guidelines. Primary outcomes assessed included sleep disturbance, awakenings, and falling asleep.

The study found that there was a significant probability of being highly sleep disturbed by nocturnal noise from aircraft, road, and railway. Additionally, the exposure-response relationships studied in this systematic review and meta-analysis closely agreed with the previous study at low sound levels across all traffic types, though greater disparity was noted at higher levels with aircraft noise.  The quality of evidence for these outcomes and assessment of risk of bias was moderate. However, this study was limited by potential exposure misclassification in modelling noise levels at the most exposed side of a home rather than at the bedroom. Additionally, the meta-analysis did not adjust for age, sex, socioeconomic status, and pre-existing sleep disorders. Nonetheless, this study provides confirmation that the WHO guidelines are beneficial in avoiding sleep disturbances.

Click to read the study in Environmental Health Perspectives

Image: PD

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