The lifetime risk of developing rheumatoid arthritis and six other autoimmune rheumatic diseases for both men and women has been determined by scientists.
"We estimated the lifetime risk for rheumatic disease for both sexes, something that had not been done before - separately or collectively," said first author and biostatistician at Mayo Clinic, Cynthia Crowson.
"Prevalence and incidence rates existed, but prevalence figures underestimate individual risk and incidence rates express only a yearly estimate," she added.
The researchers were looking for an accurate basis to offer an easy-to-understand average risk over a person's lifetime, knowing that risk changes at almost every age.
They used data from the Rochester Epidemiology Project, a long-term epidemiology resource based on patients in Olmsted County, Minn.
The cohort of 1,179, consisting of patients diagnosed between 1955 and 2007, allowed the team to extrapolate the nationwide estimates.
The adult lifetime risk in the US of having some kind of inflammatory autoimmune disease is 8.4 percent for women and 5.1 percent for men.
Based on year 2000 population figures, that means one woman in 12 and one man in 20 will develop one of the conditions in their lifetime.
The authors considered that a substantial risk and said their findings should encourage more research on the value of early diagnosis and intervention for people with increased genetic risk of arthritis.
They hope the new figures would help in counselling patients and in fundraising efforts to find improved treatments.
The findings appear online in Arthritis and Rheumatism.