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Study confirms link between silica exposure and rheumatoid arthritis

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A large Swedish population based study of silica exposure and its relation to rheumatoid arthritis (RA) will help our understanding of the disease process, say its authors. The results confirm those of previous smaller and less well controlled studies suggesting that silica exposure is a risk factor for RA.

Exposure to silica raised the chance of developing RA twofold for men aged 18–70 years (odds ratio (OR) 2.2) and slightly more for men aged 50–70 (OR 2.7) compared with unexposed matched controls, after adjustment for confounding factors—age, residency, and smoking. Drilling or crushing stone, associated with high silica exposure, increased the chances further (OR 3.0, 3.3, respectively). Smoking raised the chances of RA in men exposed to silica (OR 3.7) and in the controls (OR 1.4) with adjustment for confounders. Its effect might even be synergistic with silica exposure, though confirmation would need more data.

The results are part of the EIRA study—a study of incident cases of RA in men in the general population of one area of Sweden. Self reported data on exposure to silica and smoking habit in 276 men developing clinically diagnosed RA during May 1996–June 2001 and controls from a random stratified sample matched for age, sex, and residency were compared.

Little is known about environmental factors and RA. The authors of this study speculate that inflammatory processes in RA and silicosis may be similar.

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