Body size and the risk of multiple sclerosis in Norway and Italy: The EnvIMS study

Background: Obesity may be a risk factor for developing multiple sclerosis (MS). Objective: We examined if body size influences the risk of MS in a population-based, case control study. Methods: A total of 953 cases and 1717 controls from Norway and 707 cases and 1333 controls from Italy reported their body size by choosing a silhouette 1 to 9 (largest) every fifth year from age 5 to 30 and at time of study. The body size-related MS risk was defined by odds ratios (ORs) in logistic regression analyses adjusting for age, smoking and outdoor activity. Results: In Norway a large body size (silhouettes 6-9) compared to silhouette 3 increased the risk of MS, especially at age 25 (OR 2.21; 95% CI 1.09-4.46 for men and OR 1.43; 95% CI 0.90-2.27 for women). When comparing silhouette 9 to 1, we found a significant dose-response from age 10 until age 30 peaking at age 25 (sex-adjusted OR 2.83; 95% CI 1.68-4.78). The association was present for at least 15 years prior to disease onset. No significant associations were found in Italy. Conclusions: Obesity from childhood until young adulthood is a likely risk factor for MS with a seemingly stronger effect in Norway than in Italy.