Exposure to mixture particulate contaminants in the air and the risk of oral cancer: An updated systematic review and meta-analysis

The mixture of contaminants in the air (e.g., PM_2.5, smoke) is a part of air pollutants that has become a hot environmental issue. Previous epidemiological studies have reported the relationship between wood smoke and PM_2.5 exposure and oral cancer, but findings have been inconsistent. Therefore, this work designed to find out the relationship between mixture contaminants in air exposure and oral cancer. Fourteen studies were included through research in three databases before February 2024. Before analysis, the Newcastle-Ottawa Scale was applied to examine the quality of all selected studies. Then, the meta-analysis was carried out by meta-regression analysis, sensitivity analysis and subgroup analysis. The results showed that exposure to PM_2.5 may have a positive association with oral cancer (pooled OR = 1.13, 95 % confidence interval: 1.06, 1.20). In contrast, no significant association was found between indoor air pollution and oral cancer. However, the result of the subgroup analysis indicated there is a significant association of indoor air pollution and oral cancer in developing countries (pooled OR = 2.5, 95 % confidence interval: 1.7, 3.6). In addition, the heterogeneity among studies of indoor air pollution exposure and oral cancer may caused by studies carried out in developed countries according to the subgroup and meta-regression analyses. In conclusion, the studies about indoor air pollution exposure and oral cancer are discrepant. The effects of mixed air contaminants for people's health are not simple and more studies are demanded to find out it in the future.