Environmental risk factors for rheumatoid arthritis.

In this review we examine the association between rheumatoid arthritis (RA) and exposure to silica and other environmental toxicants. We performed a series of meta-analyses of peer-reviewed studies, using 10 studies for silica, and 5 studies for other exposures published between 1986 and 2001. Before the meta-analyses, all studies were reviewed and evaluated for heterogeneity and publication bias. We detected a significant heterogeneity among studies on silica and calculated a combined estimator of relative risk (RR), using the random effect model. Most studies reported consistent elevation in the risk of RA with exposure to silica. The combined RR for silica exposure was 3.43 195% confidence interval (95% CI) 2.25-5.22] for all studies, and 4.45 (95% CI 2.24-8.86) for male cohorts. The combined RR for male farmers was 1.40 [95% CI 1.18-1.66] and was 1.29 [95% CI 0.84-1.97] for pesticide exposure. The combined RR for hair dressers was 1.52 [95% CI 1.04-2.20]. The findings of this study suggest a significant elevation in the risk of RA from exposure to silica. Further studies assessing the dose-response effect would greatly aid in determining whether the observed association is causal.