Being overweight is associated with accelerated grey matter volume loss in the brain, a mark of neurodegeneration, in multiple sclerosis (MS) patients, a five-year observational study shows. But vitamin D levels, often suggested as an MS risk factor, do not seem to affect brain volume over time.
The study, “Higher body mass index, but not vitamin D status, is associated with greater subsequent loss of brain grey matter volume in multiple sclerosis,” was presented by Ellen Mowry, MD, a professor of neurology at Johns Hopkins University. She spoke at the recent 34th Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) in Berlin.
Several environmental risk factors thought to increase the susceptibility of developing MS — and possibly its severity — include smoking, vitamin D deficiency, and obesity.
Vitamin D levels have been associated with the inflammatory response and brain volume changes early in the disease. Some researchers believe that poor exposure to sunlight, which is the natural source of vitamin D, may be the reason why MS occurs more frequently in regions farther from the equator.
Recent research also suggests a possible role of this vitamin in neuroprotection and myelin repair, and several studies are currently underway to determine what other roles played by vitamin D are relevant in MS disease.
Increasing evidence also points to obesity as an important MS risk factor. Several studies have shown that obesity in childhood and adolescence increases the risk of developing MS later in life.
Being overweight may also promote inflammation and worsen disease progression and severity, with obesity-related comorbidities appearing to be linked with the overall morbidity and mortality in MS patients.
To further understand the influence that vitamin D and body weight may play in the course of the disease, a team led by researchers at Johns Hopkins and the University of Southern California investigated if blood levels of vitamin D and body mass index (BMI) were associated with the progression of neurodegeneration in the brain, and the loss of brain volume over time.
Researchers analyzed 469 people with relapsing-remitting MS (RRMS) or clinically isolated syndrome (CIS), who were followed for five years as part of the EPIC study. This is a large observational study at the University of California, ongoing since 2004, which has been carefully monitoring 500 MS patients using MRI scans, blood tests, and clinical evaluations.
In a set of analysis adjusted for age, sex, ethnicity, smoking status, and treatment use, annual levels of vitamin D in the blood (25-hydroxy vitamin D test) and BMI were compared with measures of brain size — namely, the volume of the parenchyma (the neurons and glial cells that make up functional brain tissue), and its grey and white matter.
Results showed that a rise of 1 kg/m2 in BMI was associated with an overall loss of 1.1 milliliters of grey matter volume among MS patients. The brain’s grey matter is where the cell bodies of nerve cells reside, as well as the axon terminals, the tips of nerve fibers that nerve cells use to communicate with each other.
As the disease progresses, nerve cell bodies are damaged, which may underlie the shrinking of grey matter.
Brain parenchyma, which refers to the overall brain mass, also got smaller with increases in BMI. Parenchyma volume was reduced by 1.1 ml per 1 kg/m2 of increase in BMI.
Vitamin D levels, however, showed no significant association with brain volume changes.
“Higher BMI appears to be associated with accelerated reductions in nGMV [normalized grey matter volume] and nBPV [normalized brain parenchyma volume], relevant since in particular nGMV loss portends greater longer-term disability,” the researchers wrote.
Given that obesity is a manageable factor, more studies “should explore these relationships in detail, and evaluating the effect of reducing BMI on imaging and clinical outcomes in MS may be warranted,” they concluded.
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