Body mass index during adolescence, rather than childhood, is critical in determining MS risk

Objective: Obesity in childhood and during adolescence has repeatedly been associated with increased risk of developing multiple sclerosis (MS). We aimed to investigate whether the most critical period occurs during childhood or later, during adolescence. Methods: Using a population-based case-control study (1586 cases and 2800 controls), individuals with different body sizes at age 10 and different body mass indices at age 20 were compared regarding MS risk, by calculating odds ratios with 95% confidence intervals. Potential interactions between HLA-DRB1*15 and absence of HLA-A*02, respectively, and both childhood and adolescent obesity were evaluated by calculating the attributable proportion due to interaction. Results: Regardless of body size at age 10, individuals with adolescent obesity had a 90% increased risk of MS. Among participants who were not obese at age 20, no association was observed between body size at age 10 and subsequent MS risk. An interaction was observed between the HLA MS risk genes and adolescent, but not childhood, obesity. Conclusions: Our results suggest that BMI during adolescence, rather than childhood, is critical in determining MS risk.