Young adults at age 20 who are obese and smoke are not only at a higher risk of developing relapsing multiple sclerosis — those who become MS patients after age 20 are also more likely to advance to secondary progressive MS more quickly, researchers in Sweden report.
But the link seen between obesity, defined as a body mass index greater than 30, and secondary progressive multiple sclerosis (SPMS) did not hold in MS patients who were not tobacco smokers, the researchers noted, an observation that “may give insight to disease driving mechanisms.”
Their study, “Association of Pre-Disease Body Mass Index With Multiple Sclerosis Prognosis,” and was published in the journal Frontiers in Neurology.
About 15% of MS patients are diagnosed with the primary progressive disease form (PPMS), characterized by steady worsening of neurologic symptoms from disease onset without a relapsing-remitting phase. Secondary progressive MS (SPMS) follows a course of relapsing-remitting MS (RRMS) — the most commonly diagnosed disease form — and is marked by steady symptom and disability worsening. About 70% of RRMS patients undergo conversion to SPMS.
A high body mass index (BMI; weight to height ratio) during childhood and adolescence is associated with MS development. But its impact on the conversion to the progressive disease form is not well understood.
Researchers analyzed data involving 5,598 Swedish patients (1,453 men and 4,145 women) diagnosed with MS after the age of 20, and assessed BMI data to investigate its possible link to disease progression. Because changes in BMI can be related to smoking, and an earlier study showed that smoking post-diagnosis increased the risk of faster progression to SPMS, patients’ smoking history was also considered in the analysis.
Patient data was obtained from the Genes and Environment in Multiple Sclerosis study and the Epidemiological Investigation of Multiple Sclerosis study, both part of the Swedish MS registry.
Patients were divided into three categories based on body mass: low weight (BMI under 18.5), normal to overweight (BMI of 18.5 to 30), and obese (BMI greater than 30).
The median pack years smoked before SPMS onset was 7.00 for the 688 low-weight patients; 5.50 and 5.95 for the 4,772 people normal and overweight, respectively; and 4.93 for the 158 patients in the obese group.
Researchers found that those patients who were obese at the age of 20 developed SPMS sooner (around age 51) compared to patients in the other two groups, who progressed around age 57.
Obesity at the age of 20 increased the risk of SPMS development in people who smoked before the onset of their disease. This association between adolescent obesity and increased SPMS risk was not observed in non-smokers.
Overall, these findings contribute to knowledge about risk factors associated with MS disease progression.
“BMI has been identified as a factor which not only increases the risk of developing MS but also of progressing to the SP stage, thereby offering clues as to the disease driving process,” the researchers wrote.