The influence of early life factors on the risk of developing rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic inflammatory disease that develops as a result of the interaction between genetic and environmental risk factors. Although increasing evidence shows the importance of genes in determining the risk of RA, it is clear that environmental factors also have a vital role. Studies to date have tended to concentrate on environmental influences around the time of disease onset. However, a number of pieces of evidence, including the fact that autoantibodies, such as rheumatoid factor (RF), can develop several years before the onset of clinical disease, suggest that environmental factors may influence disease susceptibility during early life. Several recent studies lend weight to this possibility, with an increased risk of RA in the offspring of mothers who smoked during pregnancy and in those with higher birth weight. There has also been a suggestion that the risk of RA is reduced in breast-fed infants. We describe the evidence surrounding the effect of early life factors on the risk of developing RA and possible mechanisms by which they may act.