Cigarette Smoking and the Risk of Systemic Lupus Erythematosus: A Meta-Analysis

Objective. Existing studies present conflicting evidence for the role of cigarette smoking as a risk factor in the development of systemic lupus erythematosus (SLE). We performed an extensive search of the medical literature for all studies examining this relationship, and performed a meta-analysis to arrive at a more precise estimate of effect. Methods. We performed a computerized literature search for all studies (in all languages), using Medline and EMBASE (1966 to present) and the Cochrane Collaboration database, and completed hand searches of relevant bibliographies and abstracts of conference proceedings. Several investigators systematically extracted data from the relevant studies. Unpublished data were obtained from the author of one abstract. Studies were examined in aggregate for heterogeneity and publication bias. The relationships of current smoking and past smoking (prior to the onset of SLE) to development of SLE were analyzed separately. Results. Fifty-two studies were identified and chosen for detailed review. Of these, 9 (7 case-control and 2 cohort studies) were appropriate for inclusion in our meta-analyses. For current smokers compared with nonsmokers, the odds ratio (OR) for development of SLE was significantly elevated (OR 1.50, 95% confidence interval [95% CI] 1.09-2.08). Former smokers, compared with nonsmokers, did not demonstrate an increased risk of SLE (OR 0.98, 95% CI 0.75-1.27). Several subgroups were also analyzed. Conclusion. Our meta-analysis of the 7 existing case-control and 2 cohort studies revealed a small but statistically significant association between current smoking and development of SLE. However, no association between past smoking and development of SLE was observed.