Palacios et al. Smoking and increased risk of multiple sclerosis: parallel trends in the sex ratio reinforce the evidence. Ann Epidemiol. 2011 Jul;21(7):536-42. Epub 2011 May 7.
Background: Smoking behavior in industrialized nations has changed markedly over the second half of the 20th century, with diverging patterns in male and female smoking rates. We examined whether the female/male incidence of MS changed concomitantly with smoking, as would be expected if smoking truly increased MS risk.
Methods: These researchers identified relevant studies reporting male and female age-specific incidence of MS throughout the world using within-country birth cohorts as units of observation. They then correlated the male/female ratio of MS incidence in each birth cohort with the corresponding male/female ratios in smoking behavior obtained from national statistics. They also examined in depth the within-country trends of smoking and MS in Canada and Denmark, two populations in which statistics on MS are readily available.
Results: The gender ratio of MS is correlated with the gender ratio of smoking (r = 0.16; 95% confidence interval [CI]: 0.06, 0.26; p = 0.002). Additionally, they estimated an overall incidence rate ratio of 1.50 (95% CI: 1.17, 2.01) of MS for ever-smokers as compared with never-smokers. The trend in the gender ratio of smoking, however, was driven by a decline in smoking among men, rather than by an increase in women as observed for MS incidence.
Conclusions: These results are consistent with the hypothesis that smoking increases the risk of MS and explains in part the divergence in MS incidence rates in men and women. However, some other factor must account for the increasing MS incidence among women.
"Interesting that MS incidence may be declining in men, relative to woman, due to the reduction in rates of smoking. Pity young girls don't understand what risks they are taking when they light up."
"The million dollar question is whether or not smoking is causal or simply associated with MS. For example, are smokers more likely to be exposed to another risk factor as a result of their behaviour compared to non-smokers? Immunologists believe that smoking damages proteins in the body, which then trigger autoimmune diseases."
"Watch this space! We need to know how smoking is related to MS."
Related posts of interest:
11 Jun 2011
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12 Apr 2011
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