Background/Purpose:

Previous reports suggest smoking may be a risk factor for developing systemic lupus erythematosus (SLE), however the significance of this relationship varies among studies. This study explores the impact of smoking and exposure to secondhand tobacco smoke on SLE compared to controls and on disease characteristics among patients.

Methods:

Data from a longitudinal cohort of SLE patients, related controls and unrelated controls was utilized. All controls were African American (AA), therefore all comparisons between patients and controls excluded non-AA patients.  Medical history, smoking and secondhand smoke exposure history, SLE Disease Activity Index (SLEDAI) and SLICC-Damage Index (SDI) scores were collected at an in-person enrollment visit and confirmed by chart review.  Active disease was defined as a SLEDAI ≥6 and disease damage was defined as SDI >0. Statistical analysis used chi square testing for proportions and multivariate logistic regression to compare groups while adjusting for covariates. 

Results:

There were 545 SLE patients and 386 controls with data available for analysis (Table). At enrollment, the mean age was 37.6 +/- 14.7 years for patients and 42.0 +/- 15.4 years for controls. Mean disease duration at enrollment was 7.0 +/- 7.5 years for patients.  Patients were 91.6% female, related controls (n=222) were 76.6% female and unrelated controls (n=164) were 86.0% female. Differences between current and never smokers (p=0.51) and ever and never smokers (p=0.70) were not significantly different between patients and controls. Compared to unrelated controls, AA patients were significantly more likely to be exposed in the home to secondhand smoke before the age of 18, adjusting for age, education level, and gender (OR 1.81, 95% CI 1.13-2.89).

SDI scores were available for 423 of the patients. Damage by SDI was significantly associated with ever smoking (OR 3.08, 95% CI 1.4-6.6), current smoking (OR 3.17, 95% CI 1.1-9.1), and secondhand smoke exposure in childhood (OR 1.91, 95% CI 1.0-3.6), adjusting for disease duration, ethnicity, baseline age, SLEDAI, hydroxychloroquine use, education level and gender.  No significant relationship was found between smoking status and either active disease at enrollment or presence of dsDNA autoantibodies. A history of discoid rash was significantly associated with ever smoking (OR 2.74, 95% CI 1.5-5.1) and current smoking (OR 4.85, 95% CI 2.2-10.5), but not with secondhand smoke exposure, adjusting for disease duration, ethnicity, baseline age, hydroxychloroquine use, education level and gender. 

Conclusion:

Our study suggests that secondhand smoke during childhood may be an important risk factor for SLE.  Secondhand smoke during childhood, in addition to current smoking and past smoking, contributes significantly to disease damage among patients with established SLE.