Cadmium, road dust and rheumatoid arthritis: an alternative hypothesis to general air pollution

We read the review "Is air pollution a risk factor for rheumatoid arthritis?"with great interest [1].We agree that air pollution is a potential risk factor for rheumatoid arthritis (RA) in low-and-middle-income countries.As the authors correctly point out, epidemiological studies in high-income countries which have failed to demonstrate a link between air pollution and the risk of RA [2, 3], can not necessarily be generalised to individuals living in lowand-middle-income countries.However, it remains that two large well conducted studies in North America have clearly demonstrated an increased risk of RA in those residing ≤ 50 m from a highway compared with residence > 150 m away [4,5].This finding is not explained by industrial pollution per se as two studies in high income countries found no consistent association between air pollution and an increased RA risk [2,3].If air pollution in high-income countries is not