Smoking linked to rheumatoid arthritis in blacks

Quitting or avoiding smoking could prevent about one-in-six of rheumatoid arthritis cases that occur in African-Americans, new study findings suggest.

U.S. researchers have linked smoking with the development of the disease in this population for the first time in a study published online in Arthritis & Rheumatism.

Although previous epidemiologic studies involving European populations have demonstrated the association between smoking and rheumatoid arthritis (RA), little was understood concerning this link in African-Americans – a population less likely to carry HLA-DBR alleles, a known RA genetic risk factor.

Among the more than 800 African-American patients (n=605) and controls (n=255) who participated in the study, those with RA were considerably more likely to be current smokers (OR= 1.56; 95% CI: 1.56-2.26) than never smokers, with the strongest link between the habit and RA established among heavy smokers with a ten or more pack-year history of smoking (OR= 2.37; 95% CI: 1.56-3.60).

“In light of reports suggesting that smoking is on the rise among African-Americans, our results suggest that [RA] incidence and disease burden may increase in this population over the next decade,” study researcher Ted R. Mikuls, MD, of the University of Nebraska in Omaha, and colleagues wrote.

Although few African-Americans who participated in the study had shared epitope HLA-DBR alleles, more than half were positive for the autoantibodies rheumatoid factor (76%) and anti-cyclic citrullinated peptide (anti-CCP; 67%).

Furthermore, the association between smoking and RA remained among both antibody-positive and antibody-negative African-American patients, despite earlier study findings suggesting an association among those European patients with only antibody-positive RA:

• Anti-CCP positive patients had a 2.35 OR (95% CI: 1.55-3.58) vs. anti-CCP negative patients with a 2.16 OR (95% CI: 1.33-3.50)
• Rheumatoid factor positive patients had a 2.43 OR (95% CI: 1.62-3.66) vs. rheumatoid factor negative patients with a 2.07 OR (95% CI: 1.23-3.50).

“The reasons for this apparent discrepancy are unknown but it is possible that there are other genetic and/or environmental factors that could mediate the effect of smoking in autoantibody negative [RA] and the prevalence of these as yet undefined factors could vary markedly in prevalence based on race/ethnicity,” the researchers wrote.