Cigarettes, not snuff, increase multiple sclerosis risk

EU-funded researchers in Sweden have discovered that while tobacco smoking raises the risk of multiple sclerosis (MS), snuff does not. The findings are published in the journal Neurology.

The research is part of the NEUROPROMISE (’Neuroprotective strategies for multiple sclerosis’) project, supported under the ‘Life sciences, genomics and biotechnology for health’ Thematic area of the EU’s Sixth Framework Programme (FP6).

Scheduled to end in 2010, NEUROPROMISE seeks to identify the major genes and critical pathways associated with MS and inflammatory neurodegeneration, as well as to elucidate the key immunopathological mechanisms of neurodegeneration. The project also aims to develop novel neuroprotective drugs based on targets validated in animal models.

MS is a chronic neurological disease affecting about 1.2% to 1.6% of Swedes. Data also show that more women suffer from MS than men. While researchers have found a genetic component in the disease, environmental factors such as smoking also play a role in increasing the risk of MS.

While eight out of nine studies investigating smoking and MS risk have shown that smokers have a greater chance of developing MS, only one study assessed ‘cumulative dose’ or the length of time people smoked, and MS risk.

The Swedish study, led by Dr Anna K. Hedström of the Karolinska Institutet, investigated whether the use of Swedish snuff affects a person’s chances of developing MS. According to Dr Hedström, Swedish snuff is different from US snuff in that it is a moist powder and usually does not involve any spitting by the user.

‘While tobacco cigarettes increased a person’s risk of developing MS, our research found that using Swedish snuff was not associated with an elevated risk for MS,’ Dr Hedström explained. ‘These results could mean that nicotine is not the substance responsible for the increased risk of MS among smokers.’

Users place the snuff under the upper lip and absorb large amounts of nicotine in the process, according to the researchers.

The team used a 2,757-strong sample comprising 902 people diagnosed with MS and 1,855 people without MS. The ages of the Swedish subjects ranged from 16 to 70. Each participant completed a questionnaire about tobacco cigarettes and snuff use.

The researchers found that for men, smokers had a 1.8-times-higher chance of having MS than non-smokers, and for women, smokers were 1.4 times more likely to have MS than non-smokers. Even moderate smokers of both sexes are at greater risk, the data showed.

Also, even if a person were to stop smoking, the risk for being diagnosed with MS remains high for up to five years, according to the study. But the researchers also discovered that taking Swedish snuff for more than 15 years decreased the risk of developing MS. It should be noted that no significant effect was found for snuff use of less than 15 years.

‘Taking snuff, however, may have other harmful effects, and our findings should not be interpreted to mean that Swedish snuff is recommended to prevent disease,’ Dr Hedström pointed out.

‘More research is needed to better understand the mechanisms behind the findings. Theories are that smoking may raise the risk of MS by increasing the frequency and persistence of respiratory infections, or by causing autoimmune reactions in genetically susceptible people.’

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