Abdominal obesity and white matter microstructure in midlife

Abstract

The aging US population and the recent rise in the prevalence of obesity are two phenomena of great importance to public health. In addition, research suggests that midlife body mass index (BMI) is a risk factor for dementia, a particularly costly disease, in later life. BMI could influence brain health by adversely impacting cerebral white matter. Recently, greater BMI has been associated with lower white matter fractional anisotropy (FA), an index of tissue microstructure, as measured by diffusion-tensor imaging (DTI) in midlife. The aim of this study was to investigate the role of abdominal obesity, the most metabolically active adipose tissue compartment, and white matter microstructure in midlife. Community dwelling participants (N=168) between the ages of 40 – 62 underwent MRI scanning at 3T and a general health assessment. Inferences were made on whole brain white matter tracts using full-tensor, high-dimension normalization and tract based spatial statistics. Higher waist circumference was associated with higher FA, indicating more directional diffusion in several white matter tracts controlling for age, sex, triglycerides, systolic blood pressure, fasting glucose, and HDL-cholesterol. Post-hoc analysis reveled that greater waist circumference was associated with lower axial diffusivity (AD), indicating lower parallel diffusion; lower radial diffusivity (RD), indicating lower perpendicular diffusion; and lower mean diffusivity (MD), indicating restricted diffusion. This is the first study to report a positive relationship between obesity and FA, indicating a more complicated view of this relationship in the aging brain.

Adipokines contribute to central-obesity related reductions in myelin-sensitive MRI indices in the fornix

“…This observation may explain discrepant findings in the literature, as some studies reported beneficial effects of larger BMI or waist circumference on white matter microstructure (Birdsill et al, 2017), whilst other studies reported adverse effects Kullmann et al, 2015;Ronan et al, 2016). Previously we reported significant correlations between BMI and fornix white matter microstructure in a smaller group of older adults (Metzler-Baddeley et al, 2013), a result that was not replicated here.…”

Inhibitory control mediates a negative relationship between body mass index and intelligence: A neurocognitive investigation

“…The observed positive relationship between FA in the UF and BMI was surprising, considering that previous studies generally find negative associations between white matter structural integrity and measures of obesity. However, indicators of increased weight have previously associated with increased white matter integrity or volume in several regions (Birdsill et al, 2017;Yokum et al, 2012). Moreover, higher FA in the UF has been found to correlate with sensitivity to punishment and reward-related activity in the nucleus accumbens (Camara, Rodriguez-Fornells, & Munte, 2010), further implicating changes in this tract with higher BMI as representative of differences in emotion and reward processing.…”

Allostatic load and disordered white matter microstructure in overweight adults

“…Obesity and TBSS studies have generally described inverse associations between waist circumference (WC) or BMI and FA in tracts involved in reward-seeking (e.g., inferior fronto-occipital fasciculi, corpus callosum, and corticospinal tract) and cognitive control (e.g., inferior and superior longitudinal fasciculi) 23 – 25 . Although contradictory findings do exist 26 , most indicate that the higher the BMI or the WC, the lower the FA 27 – 31 . In addition, studies on physiological markers of stress have found reductions in global and regional FA values 32 – 34 linked to higher cortisol levels.…”