The influence of mixed environmental air pollution on deliberate self-harm among university students: evidence from...

While people are exposed to various air pollutants, limited research exists on the combined effects of multiple pollutants on mental health, and no studies have explored the social and behavioral mechanisms of mental health issues in real-world settings. This study aimed to evaluate the association between mixed air pollutants and deliberate self-harm (DSH), as well as the potential social and behavioral mechanisms underlying these associations.

The study involved 5,025 university students, selected through a multistage survey sampling process from 22 universities in 20 cities. Participants provided information on socioeconomic characteristics and DSH via a standardized questionnaire. Regional socioeconomic status and air pollution data were obtained from a national database. Multilevel logistic regression models were used to assess the association between mixed air pollution and DSH, and a structural equation model was used to explore underlying social mechanisms.

The multilevel logistic regression model revealed that the mixed air pollution index, exposure to secondhand smoke (SHS), and the number of air pollution days were significantly associated with the likelihood of DSH, with odds ratios (OR) of 2.78 (95% CI: 1.22, 6.31) and 3.30 (95% CI: 1.67, 6.52), respectively. Significant quantitative correlations were found between the number of air pollution days and the likelihood of DSH (r = 0.5553, p < 0.0001). Structural equation modeling revealed that SHS exposure had a significant direct effect on DSH (β' = 0.7458, p < 0 0.001). In contrast, air pollution days demonstrated both a direct effect (β' = 0.3323, p < 0.001) and an indirect effect on DSH through a mediating pathway (β' = 0.054, p < 0.001).

Using nationally representative data from 20 cities in China, this study provides compelling evidence of the detrimental impact of environmental air pollution on DSH. It underscores the urgent need for stronger environmental protection policies and the development of effective mental health strategies to reduce DSH and alleviate environmental strain on mental health.