New research finds that the impact of MS is twice as high among people with food allergies.
Previous studies have proposed that allergy could have a role in multiple sclerosis (MS).
However, while they have mentioned potential candidates, such as pollen, grass, pets, drugs, and various foods, the studies have been largely inconclusive.
Now, researchers from the Partners MS Center at Brigham and Women's Hospital (BWH) in Boston, MA have conducted a study looking more closely at links between allergy and MS disease activity.
They used data on 1,349 people with MS from a study called the Comprehensive Longitudinal Investigation of Multiple Sclerosis at the Brigham and Women's Hospital (CLIMB).
CLIMB gave them survey data about "environmental, food, and drug allergies" and on disease activity from clinical questionnaires and MRI scans. The data covered the period 2011–2015.
The team reports the findings in a paper that features in the Journal of Neurology, Neurosurgery & Psychiatry.
An inflammatory, unpredictable disease
MS is an unpredictable, long-term disease that affects the central nervous system (CNS), which includes the brain, spinal cord, and optic nerves.
Experts believe that MS is an autoimmune disease, that is, one in which the immune system launches inflammatory attacks on healthy tissue as if it were a threat.
In the case of MS, the inflammatory attacks damage the fatty myelin coating that protects nerve fibers and the electrical signals they carry.
The attacks can also damage the nerve fibers themselves and the cells that make the myelin.
MS symptoms can persist and gradually get worse, or they can come and go. Although the disease can strike at any age, most people are aged 20–50 years when they find out that they have MS.
The symptoms can vary widely, depending on the extent and location of CNS damage. They can range, for example, from vision disturbances, extreme fatigue, movement difficulties, and memory and concentration problems, to tremors, slurred speech, numbness, blindness, paralysis, and more.
While it is not clear what course the disease will take in any one person, doctors recognize four main types of MS. The types vary, according to the pattern and severity of symptoms.
MS organizations suggest that there are around 2.3 million people worldwide living with the disease.
The structure of the study
Using the self-reported data, the BWH team arranged the 1,349 CLIMB individuals in four groups: environmental, food, drug, or "no known allergies."
Of the total, 586 reported having an environmental allergy, 238 said that they had a food allergy, and 574 a drug allergy. The number reporting no known allergies was 427.
The researchers then assessed MS disease activity in each of the groups. For the assessment, they used a number of "clinical and radiological variables."
The clinical variables included the number of MS attacks, or relapses, and scores on severity and disability questionnaires that the individuals had completed in the most recent clinic visit.
The radiological variables came from MRI scans on which it was possible to detect the presence and number of active lesions.
The team used data from the scans taken at the most recent visit to the clinic.
The scans came from a type of MRI that uses a contrast agent to highlight areas of active inflammation in the brain and spinal cord.
The contrast agent is a large molecule containing the element gadolinium, which cannot usually cross the blood-brain barrier that exists between the bloodstream and the CNS.
However, the contrast agent is able to cross the blood-brain barrier during active MS disease because inflammation weakens it.
Food allergy tied to double rate of active disease
A first analysis found that, compared to having no known allergies, having any allergy was associated with a 22 percent higher rate of cumulative MS attacks.
However, when the analysis ran again, this time accounting for other potential influencing factors, the link disappeared.
When the team drilled down to specific allergies, there was a different story.
Compared with having no known allergy, having a food allergy was tied to a 27 percent higher cumulative rate of MS attacks, even after accounting for potential influencing factors.
The link between active disease and allergy was even more striking. The odds that the MRI scans would show evidence of active disease was higher for any allergy, compared with no known allergies.
However, the odds that the food allergy group would show MRI evidence of active disease was double that of the no known allergies group.
The team found no links between scores of severity or disability and any form of allergy.
Further studies need to confirm findings
Because the study looked at a snapshot of the disease at a certain point in time, the analysis cannot examine cause and effect.
The researchers could not, therefore, conclude whether having allergies causes or worsens MS, and neither could they say whether having MS causes or worsens allergies.
Other studies have suggested, however, that allergies may aggravate inflammation in MS and that this might be linked to genetic factors that MS and other autoimmune diseases have in common.
Another potential explanation could be that, through their influence on gut bacteria, food allergies might alter chemicals that affect the CNS.
Another factor that limits the recent investigation is that much of the data came from self-administered surveys. This emphasizes the need for further studies to confirm the results.
The authors conclude:
"Our findings suggest that MS patients with allergies have more active disease than those without, and that this effect is driven by food allergies."