Long-term exposure to nitrogen dioxide and natural-cause and cause-specific mortality in Japan.

BACKGROUND

Long-term exposure to air pollution is linked with increased risk of adverse health outcomes, but the evidence for the association between nitrogen dioxide (NO2) and mortality is weak because of the inadequate adjustment of potential confounders and limited spatial resolution of the exposure assessment. Moreover, there are concerns about the independent effects of NO2. Therefore, we examined the association between NO2 long-term exposure and all-cause and cause-specific mortality.

METHODS

We included participants who were enrolled in health checkups in Okayama City, Japan, in 2006 or 2007 and were followed until 2016. We used a land-use regression model to estimate the average NO2 concentrations from 2006 to 2007 and allocated them to the participants. We estimated hazard ratios (HRs) for a 10-μg/m3 increase in NO2 levels for all-cause or cause-specific mortality using Cox proportional hazard models.

RESULTS

After excluding the participants who were assigned with outlier exposures, a total of 73,970 participants were included in the analyses. NO2 exposure was associated with increased risk of mortality and the HRs and their confidence intervals were 1.06 (95% CI: 1.02, 1.11) for all-cause, 1.02 (0.96, 1.09) for cardiopulmonary, and 1.36 (1.14, 1.63) for lung cancer mortality. However, the elevated risks became equivocal after the adjustment for fine particulate matter except lung cancer.

CONCLUSION

Long-term exposure to NO2 was associated with increased risk of all-cause, cardiopulmonary, and lung cancer mortality. The elevated risk for lung cancer was still observable even after adjustment for fine particulate matter.