Exposure to cigarette smoke is emerging as an environmental risk factor for multiple sclerosis (MS). We investigated the possible association between environmental tobacco smoke, its cumulative exposure, and MS risk. We used data from the Iranian Multiple Sclerosis Registry to identify a case-control of 662 patients who had MS and a comparison group of 394 patients. Information regarding current smoking status, including the number of cigarettes smoked per day, duration, and smoking pack-years indicative of cumulative dose of tobacco smoked was obtained. We analyzed the incidence of MS among ever-smokers who had been smokers during their disease course and prior to disease onset in comparison with never-smokers who had never been exposed by calculating the odds ratio (OR) with a 95% confidence interval (CI) employing logistic regression. Of the 662 MS patients, there were 523 women (79.0%) and 139 men (21.0%), with a mean age of 31 ± 10.0 years at disease onset. The risk for MS was increased among ever-smokers (OR = 1.78, 95% CI = 1.22-2.59, p = 0.03) compared to never-smokers. As compared with never smokers, the OR for patients with 6-10 pack years was 2.91 for men (95% CI = 1.11-9.47, p = 0.03) and 1.69 for women (95% CI = 1.02-6.45, p = 0.04). Our results demonstrate that cigarette smoking is significantly associated with an increased risk for MS. The risk effects of smoking were more noticeable in male patients and at higher tobacco doses.
Keywords: Case–control; Iran; Multiple sclerosis; Risk factors; Sex ratio; Smoking.
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