Body mass index, but not vitamin D status, is associated with brain volume change in MS

To determine whether body mass index (BMI) or vitamin D status is associated with MRI measures of neurodegeneration in a cohort of individuals with relapsing-remitting multiple sclerosis (RRMS) or clinically isolated syndrome (CIS).

Expression, Proteomics, Imaging, Clinical (EPIC) is a longitudinal multiple sclerosis (MS) cohort study at the University of California, San Francisco. Participants had clinical evaluations, brain MRI, and blood draws annually. We evaluated patients with CIS or RRMS at baseline. In multivariate repeated-measures analyses adjusted for age, sex, ethnicity, smoking status, and use of MS treatments, annual 25-hydroxyvitamin D levels and BMI were evaluated for their association with subsequent brain volumes (normalized gray matter [nGMV], brain parenchymal [nBPV], and white matter volumes, as determined by Structural Image Evaluation using Normalization of Atrophy-X).

Among 469 participants, each 1-kg/m² higher BMI was independently associated with reduced nGMV in multivariate models (-1.1 mL, 95% confidence interval [CI] -1.8 to -0.5, p = 0.001). BMI was likewise independently associated with nBPV (nBPV per 1-kg/m² greater BMI: -1.1 mL, 95% CI -2.1 to -0.05, p = 0.039). Vitamin D levels did not appear to be meaningfully associated with brain volumes.

Higher BMI appears to be associated with greater reductions in nGMV and nBPV, which is relevant because, in particular, nGMV loss portends greater longer-term disability. Because obesity is modifiable, further studies should explore these relationships in detail, and evaluating the effect of reducing BMI on imaging and clinical outcomes in MS may be warranted.