Smoking, obesity interact to drive faster MS progression, study finds
Data analyzed from more than 3,300 patients to observe 'synergistic effect'
Smoking and obesity are both independently associated with faster disease progression in multiple sclerosis (MS), but when both risk factors are present together, a synergistic effect results in faster disease progression than can be explained by either alone.
“Smoking and obesity significantly interacted to increase the risk of disability worsening and cognitive decline in MS,” wrote the researchers in the study, “Smoking and Obesity Interact to Adversely Affect Disease Progression and Cognitive Performance in Multiple Sclerosis,” which was published in the European Journal of Neurology. “The significant additive interactions observed across most outcomes suggest that smoking and obesity may partly share common biological pathways contributing to MS progression.”
MS is caused by inflammation in the brain and spinal cord that drives worsening physical disability and cognitive impairment over time. Studies show that MS progression tends to be faster in people who smoke or are obese, likely because the two risk factors are tied to chronic inflammation.
Studies in other conditions, such as diabetes and heart disease, suggest obesity and smoking can interact to lead to more disease worsening than with either factor alone. Here, researchers analyzed data from more than 3,300 MS patients followed through a Swedish registry to see if this synergistic effect was also observed in MS. The patients had completed a standardized questionnaire about environmental exposures and lifestyle habits.
Increasing the risk of disease progression
Consistent with previous research, results showed that both smoking and obesity are independently associated with faster disease progression, as assessed with the Expanded Disability Status Scale (EDSS), a measure of disability, and the physical component of the MS Impact Scale 29, which assesses how MS impacts physical functioning.
Smoking, but not obesity, was also independently associated with an increased risk of cognitive issues. The effects of smoking and obesity on most of these measures are amplified when both risk factors are present at the same time, the results also suggested.
As an example, the odds of patients reaching an EDSS score of 4, which represented significant disability but without walking problems, was increased by 21% among non-obese patients who smoked and by 33% among obese patients who didn’t smoke. For obese smokers, the odds increased by 86%. Similar differences were seen for other measures of physical disability as well as cognitive tests.
“Our findings indicate that smoking and obesity interacted on the additive scale to increase the risk of disability progression in MS across most outcomes, with each factor individually contributing to increased risk and an amplified effect when both exposures were present,” the researchers wrote.
Statistical analyses suggested obesity amplifies the negative impact of smoking, not the other way around. The researchers said this is likely because obesity doesn’t change on a day-by-day basis, whereas the amount a person smokes can vary substantially over short stretches of time.
“These results highlight a complex interplay between these exposures, where persistent inflammation from obesity may enhance the detrimental effects of intermittent or sustained smoking,” the researchers wrote.
About the Author
