What are the risk factors for developing rheumatoid arthritis?

There are a number of factors that have been associated with increased risk of developing RA, including female sex, genetics, and environmental factors. Some of the environmental risk factors include a history of smoking, exposure to silica (via dust or occupational exposure) or infectious agents, vitamin D deficiency, and obesity. There is also a significant genetic component to RA. Studies in twins have estimated that RA may have around 60% heritability.^[1] Certain variants of the human leukocyte antigen (HLA) genes, which encode proteins that are important for the function of the immune system, have strong risk associations with RA.