Is Too Noisy as Bad as Too Quiet? The Inverted U-shaped Relationship between Noise and Sleep Duration

Sleep is a crucial behavioral determinant of physical and psychological well-being. With the rapid urbanization of China, noise pollution has become a growing concern, and its impact on sleep has raised substantial public health attention. This study aims to investigate the potential non-linear relationship between environmental noise and individual sleep duration, and the moderating roles of urban green space and city size.

We conducted a longitudinal analysis using data from the China Health and Retirement Longitudinal Study. City-level noise exposure was quantified using the Baidu Noise Index, a novel approach in this context. Data on urban population and green space coverage were obtained from the National Bureau of Statistics of China. Fixed-effects regression models were employed to estimate the impact of noise on sleep duration, and moderation analysis was applied to explore the roles of green space and city size.

An inverted U-shaped association was observed between noise levels and sleep duration (linear β = 0.746, P < 0.001; quadratic β = -0.955, P < 0.001), with an inflection point at 0.391 [95% confidence interval (CI): [0.320, 0.566]]. Moreover, this inverted U-shaped pattern was attenuated in cities with higher green space coverage (quadratic interaction β = 0.822, P < 0.05) and larger population (quadratic interaction β = 1.072, P < 0.001).

This study underscores the multifaceted relationship between noise exposure and sleep duration, providing a theoretical foundation for urban planning and health policy formulation, particularly in optimizing urban sound environments and promoting green space development.