Low lifelong exposure to cigarette smoking associated with RA risk

Lifelong cigarette smoking was associated with the risk for developing rheumatoid arthritis, with an increased risk even at a low level of exposure and a plateau at 20 pack-years, according to recent study results.

Daniela Di Giuseppe, PhD student, division of nutritional epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, and colleagues conducted a search of Medline and Embase for relevant studies published from 1966 to October 2013. A dose-response, random-effects, meta-regression analysis was conducted on studies reporting relative risks or odds ratio estimates for the association between pack-years of cigarette smoking and rheumatoid arthritis (RA).

Daniela DiGiuseppe MD 

Daniela Di Giuseppe

Three prospective cohort studies and seven case-control studies, including 4,552 RA cases, were analyzed. Heterogeneity was not indicated in the studies (P=.32), and results were not affected by publication bias. People who smoked 1 to 10 pack-years of cigarettes had a relative risk of 1.26 (95% CI, 1.14-1.39) for RA compared with never smokers, while smokers with 21 to 30 pack-years had an RR of 1.94 (95% CI, 1.65-2.27). No significantly greater risk for higher smoking exposure levels was observed.

Rheumatoid factor (RF)-positive RA cases had a significantly greater risk for RA (RR=2.47; 95% CI, 2.02-3.02) than RF-negative cases (RR=1.58; 95% CI, 1.15-2.18), when highest vs. lowest categories of pack-years for individual studies were compared.

“Our study showed some evidence of a nonlinear dose-response relationship between lifelong smoking and risk of RA,” the researchers concluded. “The risk increased already at a relatively low level of lifelong exposure to smoking [≤10 pack-years] and stabilized to approximately a double risk for a smoking exposure higher than 20 pack-years.”

Disclosure: The researchers report no relevant financial disclosures.