36% the over 50s in Ireland are obese based on body mass index (BMI: reflective of fat store peripherally) while 52% are ‘centrally obese’ based on waist circumference (indicative of fat located viscerally).(1) Visceral fat is thought to be a major site for inflammatory cytokine production and has been linked to other vascular risk factors such as hypertension and diabetes,(2) potentially providing a mechanism for brain atrophy.(3) The aim of the present work was to examine associations between obesity and grey matter (GM)/white matter (WM) perfusion as measured using pseudo-continuous arterial spin labelling (pCASL) MRI.

This study was embedded within the Irish Longitudinal Study on Ageing (TILDA), a nationally representative sample of > 8,000 older adults.(4) At wave three, 561 participants underwent brain MRI using a 3T scanner (Achieva, Philips, Netherlands); after exclusions, 484 participants data were included for this analysis. Cerebral blood flow (CBF [ml/100g/min]) values were calculated and their associations with BMI and waist-to-hip ratio (WHR) measures modelled using multiple linear regression. We also examined 6 groups: ‘normal’, ‘overweight’, and ‘obese’ as defined by BMI, with and without central obesity, as defined by WHR.(5) Models were adjusted for age, sex, smoking, alcohol consumption, physical activity, education, heart disease, hypertension, anti-hypertensive use, and depression.

The mean age was 69 years (± 7.2 years); 52% were female. Higher BMI and WHR were both related to lower GM and WM CBF: BMI per 1 SD (GM: β:-1.451, 95%CI:-2.300 to -0.607, P < 0.001; WM: β:-0. 575, 95%CI:-0. 939 to -0.210, P = 0.002) and WHR (GM: β:−1.667, 95%CI:−2.856 to −0.477, P = 0.006; WM: β:−0.688, 95%CI:−1.178 to −0.197, P = 0.006). The combination of overall obesity (BMI ≥ 30 kg/m2) and central obesity (WHR > 0.85[female], > 0.90[male]) was associated with lower CBF (GM: β:-4.303, 95%CI:-7.015 to -1.591, P = 0.002; WM: β:-2.029, 95%CI:-3.185 to -0.873, P < 0.001) compared to subjects without central obesity (GM: β:-0.959, 95%CI:-6.490 to 4.572, P = 0.733; WM:β:-0.051, 95%CI:-2.060 to 1.958, P = 0.960).

Our results show that central adiposity is a risk factor for impaired cerebral perfusion independent of BMI. Recent studies have shown that accumulation of fat in this area is a risk factor for cognitive impairment(6) and thus this study could partly explain the vascular origins.