The main confirmed risk factors for the illness are sex, ethnicity, and genes.
Women tend to be more affected by MS than men, as are people of European descent and those with a genetic predisposition.
While these are factors outside of our control, some studies have also pointed to other "changeable" risk factors, such as being exposed to toxic substances and having too much salt in our diet.
These are things we can all change or avoid. New research adds to the evidence that exposure to solvents is indeed a significant risk factor for developing MS, and that smoking — another changeable factor — amplifies this risk considerably.
Dr. Anna Hedström — from the Karolinska Institutet in Stockholm, Sweden — is the lead author of the new study. The findings were published in the journal Neurology.
Risk raised by genes, smoking, and solvents
Dr. Hedström and colleagues started from the assumption that lung irritation caused by different sources may trigger an immune response that would ultimately lead to MS in people who were already genetically predisposed.
To examine whether this was true, the researchers looked at a sample of 2,042 Swedish people who had received an MS diagnosis and compared them with a control sample of 2,947 sex- and age-matched people.
Blood tests revealed if the participants were genetically prone to developing MS — that is, whether they had a so-called human leukocyte antigen gene variant.
Also, the participants were asked whether they smoke or used to smoke, and whether they had been exposed to paint, varnish, or organic solvents.
Avoid smoking and exposure to solvents
The study found 139 people with MS and 525 MS-free participants in the group that did not have the MS genes, did not smoke, and had not been exposed to solvents.
In the group that had people with genetic predisposition to MS and solvent exposure but did not have any people who smoked, 34 developed MS and 19 were MS-free.
And, in the group that had all three risk factors, 40 individuals were diagnosed with MS and five were not.
Overall, based on the above, Dr. Hedström and team concluded that MS genes combined with solvent exposure accounted for around 60 percent of the risk of developing the condition.
More specifically, exposure to solvents put people at a 50 percent higher risk of MS compared with people who have not been exposed to such substances — and if we add the genetic predisposition to this, the likelihood becomes seven times higher.
Importantly, adding smoking to this already dangerous "cocktail" makes the risk soar. Compared with people who have none of the three risk factors, having all three puts a person at a 30-fold higher risk of developing MS.
"These are significant interactions where the factors have a much greater effect in combination than they do on their own," explains Dr. Hedström.
"More research is needed to understand how these factors interact to create this risk," she adds. "It's possible that exposure to solvents, and smoking may both involve lung inflammation and irritation that leads to an immune reaction in the lungs."
In an accompanying editorial, Dr. Gabriele C. DeLuca — of the University of Oxford in the United Kingdom — says, "How this cocktail of MS genes, organic solvents, and smoking contributes so significantly to MS risk warrants investigation."
"In the meantime, avoiding cigarette smoke and unnecessary exposure to organic solvents, particularly in combination with each other, would seem reasonable lifestyle changes people can take to reduce the risk of MS, especially in people with a family history of the disease."
Dr. Gabriele C. DeLuca