Long-term exposure to nitrogen dioxide and mortality: A prospective cohort study in urban and rural regions of China

Abstract

BACKGROUND AND AIM: Several epidemiology studies found nitrogen dioxide (NO2) to be linked to increased mortality. We aim to better understand the concentration-response relationship between NO2 and mortality in China. METHODS: We used Chinese Longitudinal Healthy Longevity Study (CLHLS) data. The participants were enrolled in 2008 or 2009 and followed up to 2019 roughly every two years. We obtained annual nitrogen dioxide (NO2) concentration at 1km spatial resolution using a previously validated model. We used Cox proportional hazards model to examine the association between one-five years average NO2 exposure and all-cause mortality, adjusted for demographics and lifestyle factors. We used the restricted cubic spline to describe the concentration-response relationship. Possible effect modifiers were tested. RESULTS:Our study included 13,398 individuals. We had 62,524 person-year follow-ups and 9309 mortality events. The average exposure of NO2 in the mortality year was 9.81 ppb (SD:7.29), which was higher in urban, northern and eastern regions of China. Higher NO2 was associated with higher risk for mortality, and HR (95% CI) for per ppb increase were 1.012 (1.009, 1.015), 1.008 (1.005, 1.011), 1.004 (1.001, 1.007), 1.004 (1, 1.007), and 1.004 (1.001, 1.008) for one to five years average NO2 respectively. Compared to the lowest quartile of mortality year average NO2, higher quartiles had higher risk for mortality [HR (95% CI): 1.03 (0.971, 1.093) for quartile 2; 1.223 (1.155, 1.296) for quartile 3; 1.319 (1.24, 1.404) for quartile 4]. The spline fit for NO2 was supralinear, which indicated that marginal changes in risk was larger for low concentrations compared with higher values. We also found the effect of NO2 was stronger in rural areas, younger participants, and those with less education. CONCLUSIONS:We found an association that higher NO2 exposure is associated with higher mortality. The association was stronger within lower range concentrations and rural areas. KEYWORDS: NO2, nitric oxide, traffic, mortality, longevity, China