Rheumatoid arthritis affects people of all races and ethnic groups in all countries of the world. In the United States, at least two-and-a-half million people have RA. Worldwide, this disease affects between 1-2% of the total adult population. Its incidence ranges from 0.3 to 1.5% in most populations of the world. Western countries generally see between 1-3% of their populations affected. Some Native American tribes, such as the Yakima, Chippewa and Inuit have higher frequencies of the disease, ranging from 3.5 to 5.4%.

It is hard to predict exactly who will get RA, but years of research have revealed these general risk factors:

Sex. Women are three times more likely to get RA than men. In the US, 71% of all RA patients are women. There are 1.5 million women patients, compared to 600,000 male patients. Women are slightly less likely to get RA if they have been pregnant, but the chances of getting it are increased during the first three months after giving birth. As people age, the ratio of women to men becomes more even, with the incidence becoming almost equal among elderly RA patients.

Researchers are not sure whether males are somehow protected from RA or whether females are just more susceptible to it. It seems probable that females may be susceptible due to hormonal factors, since the incidence of RA among women declines after women reach age 50. Age. RA can strike the very young or the very old. Typically, however, it is a disease of young adulthood and middle age. Most people get RA between the ages of 20 and 45.

Genetics. Rheumatoid arthritis tends to cluster in families, clearly demonstrating that there is genetic susceptibility to this disease. Those who have relatives with RA are at greater risk for the disease. Studies have shown that when a person with RA has an identical twin, both twins will have RA 30% of the time. Among fraternal twins (non-identical), both will have RA only 5% of the time. Genes influencing severity of the disease also play a role. When RA is severe, it is more likely that identical twins will both have the disease.

A gene loci known as HLA-DR4 is common among Caucasian people who have rheumatoid arthritis. Most identical twins with RA have HLA-DR4.

Other Risk Factors. Some studies have identified other factors that may increase a person's risk of getting rheumatoid arthritis. These include:

Smoking

A history of blood transfusions

Obesity

A Dutch study found that people who suffer from hay fever are more likely not to get RA, noting also that RA patients are less likely to get hay fever.

References

First published September 1, 1999
Last updated December 16, 2002
Copyright © 1999 Accordant Health Services, Inc. All Rights Reserved.

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