Systematic review and meta-analysis of epidemiological studies on the association of occupational exposure to free crystalline silica and systemic lupus erythematosus

Objectives. Some evidence suggests that exposure to free crystalline silica may contribute to the risk of developing SLE. A systematic search was carried out for all published epidemiological studies concerning this association. A meta-analysis was conducted on relevant studies. Methods. We searched PubMed and EMBASE databases for original articles published from 1960 to November 2019 in any language. In addition, we also searched the reference lists of included studies manually for additional relevant articles. Finally, seven studies were included in the systematic review and six studies in the meta-analysis (four case-control and two cohort studies). The odds ratio and 95% CI were calculated using a random effect meta-analysis. Results. The meta-analysis of the studies, applying a random effect model, yielded an overall odds ratio of 3.49 (95% CI, 1.24, 9.83), with I-2 = 92.36% (pronounced heterogeneity). We also stratified the meta-analysis by study design; case-control studies: odds ratio 1.85 (95% CI, 0.96, 3.59) with I-2 = 75.92%; and cohort studies (cases with silicosis): odds ratio 9.71 (95% CI, 1.13, 83.58) with I-2 = 72.65%. Conclusions. The obtained results support the hypothesis of a possible association between occupational exposure to free crystalline silica and SLE, in particular at higher exposure levels, known to induce silicosis. The studies that have investigated this association are still scarce and the heterogeneity between the studies remains high. New studies are deemed necessary to confirm the association.