title: Impact of smoking as a risk factor for developing rheumatoid arthritis: a meta-analysis of observational studies.
abstract: OBJECTIVE
  To assess whether smoking is a risk factor for developing rheumatoid arthritis (RA).
  
  
  METHODS
  Meta-analysis.
  
  
  METHODS
  
  
  
  METHODS
  were observational studies that examined the association between smoking history and the risk of developing RA identified through Medline and EMBASE (from 1966 to December 2006), relevant books and a reference search. Two authors independently extracted the following: 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 were based upon random effects model. Summarised syntheses effects were expressed by OR.
  
  
  RESULTS
  Sixteen studies were selected from among 433 articles. For men, summary OR for ever, current and past smokers were 1.89 (95% CI 1.56 to 2.28), 1.87 (1.49 to 2.34) and 1.76 (1.33 to 2.31), respectively. For rheumatoid factor-positive (RF+) RA, summary OR for ever, current and past smokers were 3.02 (2.35 to 3.88), 3.91 (2.78 to 5.50) and 2.46 (1.74 to 3.47), respectively. Summary OR for 20 or more pack-years of smoking was 2.31 (1.55 to 3.41). For women, summary OR for ever, current and past smokers were 1.27 (1.12 to 1.44), 1.31 (1.12 to 1.54) and 1.22 (1.06 to 1.40), respectively. For RF+ RA, summary OR for ever, current and past smokers were 1.34 (0.99 to 1.80), 1.29 (0.94 to 1.77) and 1.21 (0.83 to 1.77). Summary OR for 20 or more pack-years of smoking was 1.75 (1.52 to 2.02).
  
  
  CONCLUSIONS
  Smoking is a risk factor for RA, especially RF+ RA men and heavy smokers.
authors.affiliation: Department of Clinical Pathology and Immunology, Kobe University Graduate Schoolof Medicine, Kobe 650-0017, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Sugiyama
authors.forename: K
authors.initials: K
authors.lastname: Nishimura
authors.forename: K
authors.initials: K
authors.lastname: Tamaki
authors.forename: G
authors.initials: G
authors.lastname: Tsuji
authors.forename: T
authors.initials: T
authors.lastname: Nakazawa
authors.forename: A
authors.initials: A
authors.lastname: Morinobu
authors.forename: S
authors.initials: S
authors.lastname: Kumagai
mesh_terms: D000328:Adult; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000453:epidemiology / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017594:Publication Bias; D012107:Research Design; D012217:Rheumatoid Factor / Q000097:blood; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology
chemical_list: D012217:Rheumatoid Factor