Cigarette smoking is significantly associated with increased susceptibility to multiple sclerosis (RR 1.48; 95% CI 1.35-1.63; p < 10⁻¹⁵).
Meta-Analysis (n=460,671)
Does cigarette smoking increase multiple sclerosis susceptibility and progression?
Cigarette smoking significantly increases the susceptibility to multiple sclerosis, though its effect on disease progression remains uncertain due to study heterogeneity.
Effect estimate: RR 1.48 (95% CI 1.35-1.63)
p-value: p=< 10⁻¹⁵
BACKGROUND: Multiple sclerosis (MS) is a leading cause of disability in young adults. Susceptibility to MS is determined by environmental exposure on the background of genetic risk factors. A previous meta-analysis suggested that smoking was an important risk factor for MS but many other studies have been published since then. METHODS/PRINCIPAL FINDINGS: We performed a Medline search to identify articles published that investigated MS risk following cigarette smoking. A total of 14 articles were included in this study. This represented data on 3,052 cases and 457,619 controls. We analysed these studies in both a conservative (limiting our analysis to only those where smoking behaviour was described prior to disease onset) and non-conservative manner. Our results show that smoking is associated with MS susceptibility (conservative: risk ratio (RR) 1.48, 95% confidence interval (CI) 1.35-1.63, p < 10⁻¹⁵; non-conservative: RR 1.52, 95% CI 1.39-1.66, p < 10⁻¹⁹). We also analysed 4 studies reporting risk of secondary progression in MS and found that this fell just short of statistical significance with considerable heterogeneity (RR 1.88, 95% CI 0.98-3.61, p = 0.06). DISCUSSION: Our results demonstrate that cigarette smoking is important in determining MS susceptibility but the effect on the progression of disease is less certain. Further work is needed to understand the mechanism behind this association and how smoking integrates with other established risk factors.
Handel et al. (Thu,) conducted a meta-analysis in Multiple sclerosis (n=460,671). Cigarette smoking vs. Non-smoking (controls) was evaluated on MS susceptibility (conservative analysis) (RR 1.48, 95% CI 1.35-1.63, p=< 10⁻¹⁵). Cigarette smoking is significantly associated with increased susceptibility to multiple sclerosis (RR 1.48; 95% CI 1.35-1.63; p < 10⁻¹⁵).