Smoking and multiple sclerosis: an updated meta-analysis.
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.


RESULTS
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).


CONCLUSIONS
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.
Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom.
Adam E
AE
Handel
Alexander J
AJ
Williamson
Giulio
G
Disanto
Ruth
R
Dobson
Gavin
G
Giovannoni
Sreeram V
SV
Ramagopalan
D018450:Disease Progression; D004198:Disease Susceptibility; D006801:Humans; D009103:Multiple Sclerosis / Q000453:epidemiology / Q000209:etiology; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*
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