Effects of vitamin D on associations between air pollution and mental health outcomes in Korean adults: Results from the Korea National Health and Nutrition Examination Survey (KNHANES)

Background: Evidence suggests that low individual vitamin D levels enhance adverse effects associated with air pollution on mental health conditions. The aim of this study was to identify associations between ambient air pollution exposure, mental health, and serum vitamin D status in the general population of South Korea.Methods: We included national representative data for 29,373 adults in the final analysis. We measured serum 25-hydroxyvitamin D concentrations to assess vitamin D status for each participant. We assessed mental health factors (i.e., perceived stress, depressive symptoms, and suicidal ideation), and analyzed associations between these factors and individuals' annual average exposures to air pollutants, including particulate matter with an aerodynamic diameter <= 10 mu m (PM10), nitrogen dioxide (NO2), sulfur dioxide, and carbon monoxide (CO).Results: Using an adjusted model, we found PM10 affected mental health outcomes, such as perceived stress (odds ratio [OR] = 1.04; 95 % confidence interval [CI] = 1.00-1.09), depression symptoms (OR = 1.12; 95 % CI = 1.06-1.18), and suicidal ideation (OR = 1.11; 95 % CI = 1.05-1.17). Effects of the pollutants NO2 and CO were significant only in the group with perceived stress and depressive symptoms. PM10 and NO2 exposures were significantly associated with increased odds of adverse mental health in participants with vitamin D deficiency. Limitations: Since the cross-sectional design of KNHANES data, it is not possible to evaluate the causal rela-tionship between air pollution exposure, vitamin D status and mental health.Conclusions: This study results suggest that associations between ambient air pollution and mental health out-comes were stronger in participants with vitamin D deficiency.