Objectives: To assess whether smoking is a risk factor for developing RA, especially for RA patients who are rheumatoid factor-positive (RF+).
Methods: Data Sources: Observational studies that examining the association between smoking history and the risk for developing RA identified through Medline and EMBASE (from 1966 to December 2006), relevant books, and a reference search.
Data extraction: Two authors independently extracted the followings; authors names, publication year, sample size, participant characteristics, odds ratios (OR) or relative risks, adjustment factors, study design, and area where the study was conducted. Data syntheses: Data syntheses were based upon the DerSimonian-Laird random effect model. Summarized syntheses effects were expressed by odds ratios.
Results: Sixteen studies were selected from among 433 retrieved articles. Data syntheses were based on the random effect model. For male, summary ORs for ever, current, and past smokers were 1.89 (95% confidence interval [CI], 1.56-2.28), 1.87(1.49-2.34) and 1.76(1.33-2.31), respectively. For RF+ RA, the summary ORs for ever, current, past smokers were 3.02(2.35-3.88), 3.91(2.78-5.50), and 2.46(1.74-3.47), respectively. Summary OR for 20 or more pack-years of smoking was 2.31(1.55-3.41). For female, summary ORs for ever, current, and past smokers were 1.27(1.12-1.44), 1.31(1.12-1.54) and 1.22(1.06-1.40), respectively. For RF+ RA, the summary ORs for ever,current, and past smokers were 1.34(0.99-1.80), 1.29(0.94-1.77), and 1.21(0.83-1.77). Summary OR for 20 or more pack-years of smoking was 1.75(1.52-2.02).
Conclusions: Smoking is a risk factor for RA for both male and is especially strongly associated with RA for RF+ male and both male and female heavy smokers.
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