Background Fine particulate matter (PM_2.5) is a serious air pollutant associated with elevated levels of C-reactive protein (CRP), an inflammatory indicator.

Objective To assess the potential impacts of long-term exposure to PM_2.5 on CRP levels based on previous epidemiological studies.

Methods PubMed, Embase, Web of Science, CNKI, and Wanfang databases were searched to screen the cohort studies published from January 1, 2000 to January 1, 2022 on the effects of long-term exposure to PM_2.5 on CRP levels. "Fine Particulate Matter", "PM_2.5", "Particulate Air Pollutants", "Ambient Particulate Matter", "CRP", "C-reactive Protein", and "High Sensitivity C-reactive Protein" in English or Chinese were the key words used in the search. The percentage change in CRP level per 10 μg·m⁻³ increase in PM_2.5 concentration in each study was extracted, followed by meta-analysis, subgroup analysis, and sensitivity analysis.

Results A total of 1241 articles were retrieved, and 7 articles were included. Random-effects models were used to merge the included data, and it was found that the percentage of CRP level increased by 10.41% (95%CI: 2.24%-18.57%, P<0.05), when PM_2.5 concentration increased by 10 μg·m⁻³, І²=84.2%. The subgroup analysis conducted with grouping based on the annual mean concentration of PM_2.5 long-term exposure showed that the intra-group heterogeneity was significantly reduced in the <15 μg·m⁻³ and the 15- μg·m⁻³ groups, and the subgroup forest analysis showed differences between the two groups. The results of sensitivity analysis showed that there was a high degree of heterogeneity among the 7 studies, and the 2 papers with the highest annual average PM_2.5 concentration were the sources of heterogeneity. The Egger test and the funnel plot indicated that no obvious publication bias was found.

Conclusion Long-term exposure to PM_2.5 can raise levels of CRP in human body.