People who have been exposed to both PFAS and PCBs are more likely to be diagnosed with multiple sclerosis (MS). These new research findings are based on analyses of blood samples from more than 1,800 individuals in Sweden, one of the most comprehensive studies to date on the influence of chemical environmental exposure on the development of MS.
Multiple sclerosis (MS) is an autoimmune disease in which both genetic and environmental factors can contribute to the risk of the disease. In the current study, researchers analysed blood from individuals who had recently been diagnosed with MS to investigate concentrations of the common environmental contaminants PFAS and PCBs.
PFAS and PCBs are collective names for a range of subsidiary groups of environmental toxins. In a first phase, the researchers studied the incidence of 14 different PFAS contaminants and three different substances that arise when PCBs are broken down in the body, called hydroxylated PCB metabolites. For each substance, the link between concentration and the odds of being diagnosed with MS was investigated.
"We saw that several individual substances, such as PFOS and two hydroxylated PCBs, were linked to an increased odds for MS. People with the highest concentrations of PFOS and PCBs had approximately twice as high odds of being diagnosed with MS, compared with those with the lowest concentrations," says Kim Kultima, who led the study.
Blood samples from 1,800 individuals analysed
The study included approximately 900 individuals who had recently been diagnosed with MS. They were compared with a control group consisting of an equal number of people without MS. The individuals with and without MS were drawn from the EIMS cohort, a nationwide collection of samples and data designed to investigate the reasons why people are affected by MS. The researchers then measured the concentrations of environmental toxins in the blood and used statistical methods to study the link between them and the odds of being diagnosed with MS.
Clear relationship seen in actual exposure as well
To better reflect the actual exposure that people experience, the researchers also investigated how the odds was affected when the substances occurred together as a mixture of chemicals.
"We could then see that an increase in total exposure was linked to a higher odds of MS, even after adjusting for previously known lifestyle and genetic risk factors. The results show that when attempting to understand the effects of PFAS and other chemicals on human beings, we need to take mixtures of chemicals into account, not just individual substances, as people are generally exposed to several substances at the same time," says Aina Vaivade, the first author of the study.
Genetic vulnerability influences links
In a final phase, the researchers also studied the relationship between inheritance, chemical exposure and the odds of being diagnosed with MS. Individuals who carry a certain gene variant have a reduced risk of MS. In individuals in the study who carried this gene variant, an unexpected increased odds of getting MS was observed in the case of higher PFOS exposure.
"This indicates that there is a complex interaction between inheritance and environmental exposure linked to the odds of MS. We therefore think it is important to understand how environmental contaminants interact with hereditary factors, as this can provide new knowledge about the genesis of MS and could also be relevant for other diseases," Kultima says.
