January 25, 2023 | News | Living with MS MS Research

Does obesity worsen MS?

A new study in Germany has examined whether people with MS who are obese do worse than those without obesity (Lutfullin and colleagues. J Neurol Neurosurg Psychiatry 2023;94:57-61). Obesity was defined as a body-mass index (BMI) of 30 or higher. This corresponds to a body weight of about 80 kg (175 lbs) for a woman who is 162 cm (5 foot 4 inches) or 102 kg (225 lbs) for a man who is 183 cm (6 feet).

The study included 1066 people with an average age of 33 years. Fifteen percent were obese at the start; of these, 6% had other medical conditions related to their obesity (e.g. high blood pressure, type 2 diabetes). Over a six-year period, people who were obese at the outset had a higher risk of developing mild disability, defined as some degree of impairment but walking ability was unaffected. The median time to develop mild disability was about 12 months in people with obesity compared to 17 months in non-obese people. Overall, about one-third of people with obesity reached a level of mild disability in the first six years compared to 14% of non-obese people. This translates to a two-fold increased risk of early disability for people who are obese.

The researchers concluded that for people newly-diagnosed with MS, those who are obese have a higher risk of early disability. But this conclusion may overstate the issue and requires some qualifications.

One theory about the role of obesity in MS is that fat tissue promotes a more inflammatory environment in the body, which can worsen the inflammation that occurs in MS. However, the German study did not find this. Obesity was not associated with more frequent symptoms and signs of MS-related inflammation (i.e. relapses and new MRI lesions). Access to an MS medication (which reduce inflammation) did not appear to play a role – about 70% of people in both groups were not on an MS therapy. Other obesity factors, such as high blood pressure or type 2 diabetes, also did not appear to worsen outcomes.

The researchers acknowledged that a limitation of the study was that BMI was only evaluated at the beginning. Body weight can fluctuate, and it would have been helpful to know if people in the obese and non-obese groups were still in their original groups six years later. A second concern is with the use of BMI itself. A BMI cut-off of 30 to distinguish those who are obese (BMI 30 or more) from those who are overweight (BMI between 25 and 30) is somewhat arbitrary. (The actual difference between being categorized as ‘overweight’ vs. ‘obese’ is 0.5 kg [1 lb].) Indeed, this study showed that being overweight was not associated with a higher risk of early disability.

It may be that obesity is associated with various genetic, metabolic or biochemical changes that can make MS worse. However, a recent study found that people with MS who had risk factors for cardiovascular disease (high blood pressure, type 2 diabetes, smoking, cholesterol level) did not have an increased risk of early disability (Arroyo-Pereiro and colleagues. Eur Neurol, epublished December 5, 2022). This was also seen in the German study: obesity-associated conditions and smoking did not appear to be contributing to the disability risk. So if obesity does directly impact MS, it may be via a more subtle mechanism that will require further research.

Another explanation is that obesity is a marker of general health or of a person’s health behaviours. Obesity may be an indicator of other factors – poor diet, lack of exercise, smoking – that may have a more direct bearing on the state of a person’s MS. If obesity does influence disability, its impact was rather small in the German study. So rather than narrowly focussing on body weight, it may be more helpful to think more positively about how to improve overall wellness in your daily life.

Watch for a review of the new generation of obesity medications in an upcoming issue of MSology.

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