Both high body mass index (BMI) and smoking tobacco are known risk factors for developing multiple sclerosis (MS). However, it is unclear whether BMI, like smoking, is a risk factor for the secondary progressive MS (SPMS) course.
Using data from MS patients with BMI and smoking information available, they examined relapsing onset patients with MS onset after 20 years of age.
Comparisons were made between smokers and non-smokers, with BMI as the main exposure. In total, 5,598 relapsing onset MS patients were included. The models demonstrated that BMI of 30 or more was associated to increased risk of SPMS in smokers. However, this association of obesity at age 20 with increased risk of SPMS was not observed in non-smokers.
Researchers concluded that since the risk is confined to smokers, the interaction observed may give insight to disease driving mechanisms.