Multiple sclerosis, or SEPmainly affects young adults, between 20 and 40 years old, and concerns nearly 2.9 million people worldwide, including around 110,000 in France. We already knew that smoking, obesity in adolescence, low vitamin D levels or infection with the Epstein Barr virus increase the risk of developing this autoimmune disease, but another risk factor has just been revealed.
PFAS, PCB: “eternal” pollutants that enter the brain
In our pots, our clothes or our tap water, “eternal pollutants” accumulate silently.
- THE PFAS are compounds used to make materials non-stick or water-repellent: stoves, textiles, fire-fighting foams, food packaging. Very stable, they persist for years in the environment and in the blood;
- THE PCBformer industrial fluids now banned in many countries, degrade into hydroxylated metabolites (OH-PCB), often more toxic and capable of crossing the blood-brain barrier.
In several European countries, including France, certain uses of PFAS are now restricted, but these compounds remain detectable in drinking water and food. A Swedish team wanted to know if these substances could be found more often in the blood of people suffering from
multiple sclerosis than in healthy volunteers.
Increased exposure to these pollutants linked to increased likelihood of multiple sclerosis
The Uppsala researchers analyzed the serum of 907 people recently diagnosed with MS and 907 controls matched on age, sex and region. Thirty-one compounds were measured, including 24 PFAS and 7 OH-PCBs, then integrated into statistical models adjusted for body mass index, smoking, sun exposure, history of mononucleosis and certain HLA genes. Witness to the persistence of these compounds, the Swedish study confirmed that despite the drop in emissions since the 2000s, blood concentrations increase with age, a sign of accumulation over time.
But the most disturbing result comes from the analysis by exposure levels. “We found that several individual substances, such as PFOS (perfluorooctanesulfonic acid) and two hydroxylated PCBs, were linked to an increased risk of multiple sclerosis. People with the highest concentrations of PFOS and PCBs were approximately twice as likely to be diagnosed with multiple sclerosis as those with the lowest concentrations.
Each doubling of the concentrations of two PCB-OHs (4-OH-CB187 and 3-OH-CB153) increased the risks of MS by 8.1% and 5.5%, respectively. The researchers also showed that a mixture of PFAS and OH-PCBs, closer to actual exposure, remained linked to increased risk, even after accounting for known risk factors.
“These results show that to understand the effects of PFAS and other chemicals on humans, it is necessary to consider mixtures of substances, not just individual substances, because individuals are typically exposed to multiple substances simultaneously.”explains Aina Vaivade, first author of the study.
A complex puzzle between genetics, pollution and infection
Followed for up to 18 years in the national registry, some patients with high levels of long-chain PFAS (like PFOA, PFOS, or PFDA) had somewhat slower progression of disability, while OH-PCB 3-OH-CB153 was associated with faster degradation, especially in men. The authors discuss possible explanations, ranging from lifestyle differences to vitamin D status, without seeing a protective property of these pollutants.
In a final phase of their study, the researchers investigated the link between heredity, chemical exposure and the risk of developing multiple sclerosis (MS). People who carry a certain genetic variant have a reduced risk of MS. In study participants carrying this genetic variant, an unexpected increase in MS risk was observed with greater PFOS exposure.
“This indicates a complex interaction between heredity and environmental exposure, linked to multiple sclerosis risks. We therefore believe that it is important to understand how environmental contaminants interact with hereditary factors, as this may provide new insights into the genesis of multiple sclerosis and could also be relevant for other diseases.“, explains Kultima.
These pollutants are classified as endocrine disruptors and it is known that the same types of receptors that govern the endocrine system also affect immune function. We can therefore logically think that these substances could affect immune function and promote the risk of developing MS. however, a single study that relies on a single measurement at the time of diagnosis does not allow us to assert that this association is causal. While waiting for additional work, limiting tobacco, monitoring your weight, correcting a vitamin D deficiency and reducing your exposure to PFAS and PCBs in water, cooking or textiles as much as possible remain common sense actions.