Epidemiology of rheumatoid arthritis: determinants of onset, persistence and outcome.

Rheumatoid arthritis (RA) is the most common chronic inflammatory joint disease. There is some evidence that it may have been brought from North America to Europe during the 18th century. Its arrival in rural parts of the developing world is still more recent. The incidence and prevalence of RA appear to have fallen in Europe, North America and Japan in the last 50 years. During this time the peak age of onset has risen. Risk factors for the development of RA include genetic factors, an adverse pregnancy outcome, smoking, obesity and recent infections. The oral contraceptive pill and some dietary constituents may be protective. Older age and female gender are risk factors both for the development of RA and for a worse outcome. This risk factor profile offers some opportunities for primary and secondary prevention. However, treatment is the greatest determinant of RA outcome.