Cigarette Smoking and the Risk of Multiple Sclerosis: A Sibling Case-Control Study in Isfahan, Iran

Abstract

Aims: We aimed to study the smoking habits of multiple sclerosis (MS) patients and their healthy siblings in Isfahan province in Iran. Methods: MS patients registered with the Isfahan MS society database were compared to their healthy siblings who served as controls. Data regarding the smoking habits of patients and their siblings were collected using a specially designed questionnaire. Conditional logistic regression was adopted to analyze the association of smoking with the risk of MS, adjusting for age and sex. Results: There were 1,606 participants with 516 cases and 1,090 controls. After adjustments for age and sex, subjects who were ever-smokers had a significant risk of developing MS [odds ratio (OR) 2.67; 95% confidence interval (CI) 1.70–4.21; p <0.001]. Past smokers (OR 8.83; 95% CI 3.98–19.60; p < 0.001) and current smokers (OR 1.84; 95% CI 1.10–3.10; p = 0.021) had a significant risk for developing MS. Disease progression (current expanded disability status scale/disease duration) was not different between smokers and nonsmokers (0.54 ±0.42 vs. 0.49 ±0.48; p = 0.61). Conclusion: Using a sibling pair method our data confirm the association between smoking and MS. A degree of confounding due to overmatching between siblings was unavoidable, but any bias would be conservative and should have lessened the effect of smoking.