STOCKHOLM, Sweden, Dec. 14 (UPI) -- More than one-third of cases of the most severe and common form of rheumatoid arthritis are linked to smoking, researchers in Sweden say.
Study author Henrik Kallberg of the Institute of Environmental Medicine at Karolinska Institute in Stockholm, Sweden, says smoking accounts for more than half of cases of people who are genetically susceptible to development of the disease.
The study involved more than 1,200 people with rheumatoid arthritis and 871 people -- ages 18-70 -- matched for age and sex, but free of the disease, Kallberg says.
Blood samples found 61 percent of those with rheumatoid arthritis had the most severe form of the disease, which is also the most common form, as judged by testing positive for anticitrullinated protein/peptide antibody.
The study, published in the Annals of the Rheumatic Diseases, found those who were the heaviest smokers -- 20 cigarettes a day for at least 20 years -- were more than 2.5 times as likely as others to test positive for anticitrullinated protein/peptide antibody. The risk dropped for ex-smokers, the longer they had given up smoking, but among the heaviest smokers, the risk was still relatively high, even 20 years of quitting smoking.
