Competing physiological pathways link individual differences in weight and abdominal adiposity to white matter microstructure

Being overweight or obese is associated with reduced white matter integrity throughout the brain. It is not yet clear which physiological systems mediate the association between inter-individual variation in adiposity and white matter. We tested whether composite indicators of cardiovascular, lipid, glucose, and inflammatory factors would mediate the adiposity-related variation in white matter microstructure, measured with diffusion tensor imaging on a group of neurologically healthy adults (N=155). A composite factor representing adiposity (comprised of body mass index and waist circumference) was associated with smaller fractional anisotropy and greater radial diffusivity throughout the brain, a pattern previously linked to myelin structure changes in non-human animal models. A similar global negative association was found for factors representing inflammation and, to a lesser extent, glucose regulation. In contrast, factors for blood pressure and dyslipidemia had positive associations with white matter in isolated brain regions. Taken together, these competing influences on the diffusion signal were significant mediators linking adiposity to white matter and explained up to fifty-percent of the adiposity-white matter variance. These results provide the first evidence for contrasting physiological pathways, a globally distributed immunity-linked negative component and a more localized vascular-linked positive component, that associate adiposity to individual differences in the microstructure of white matter tracts in otherwise healthy adults.