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ndividuals with multiple sclerosis
are more likely to experience higher levels of disease activity if they also
have food allergies, according to recent research.
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."
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