Occupational exposure to paint, varnish, and other organic solvents and exposure to cigarette smoke increased the risk of people developing multiple sclerosis (MS) by 50 percent. The risk was even greater among those with a genetic predisposition to MS. These are the findings of a Swedish population-based, case-control study published online in Neurology on July 3.
More than 400,000 people in the United States and 2.1 million worldwide have MS, an autoimmune disease of the central nervous system that damages the myelin sheath, a fatty coating that protects the nerves. It can also damage the nerve fiber itself. The disease may be linked to specific genes and environmental triggers, including infection from the Epstein-Barr virus, a vitamin D deficiency, sun exposure, adolescent obesity, and smoking.
Several studies, including a 2011 study published in the journal Brain, found that smokers with a genetic predisposition to MS had a higher risk of developing MS.
In addition, exposure to organic solvents such as paint and varnish, which, like smoking, are sources of lung irritation and inflammation, is considered a risk factor for autoimmune diseases such as MS.
To test their hypothesis that lung irritation and inflammation from environmental sources can trigger an immune response that may lead to MS in genetically predisposed people, a team of Swedish researchers recruited 2,042 Swedes with MS and 2,947 healthy controls matched by sex and age between April 2005 and December 2013.
Participants completed questionnaires asking about exposure to environmental toxins such as cigarette smoke, organic solvents, painting products, and varnish. The researchers also collected blood samples to identify participants who carried one of two MS-related genes.
After the researchers analyzed participants' answers on the questionnaires regarding environmental exposure and lifestyle factors, and reviewed their blood samples, they found the risk of developing MS is seven times higher in those exposed to organic solvents with a family history of MS. People who are exposed to organic solvents, have a history of smoking, and a family history of MS, are 30 times more likely to develop the condition.
The results demonstrate that the combination of exposure to organic solvents and smoking—two sources of lung irritation and inflammation—and a genetic predisposition to MS increases the risk of developing MS more than each of these factors do separately.
The researchers suspect the immune response from lung irritation is what results in MS, especially in those with a genetic susceptibility to the disease.
Additional research with a larger data set is needed to investigate the interaction between organic solvents, smoking, and genetic risk factors for MS among women and men, according to the study authors.
The researchers emphasize that their study does not prove a cause and effect relationship as the exact cause of MS still remains unclear.