Obesity is associated with reduced cerebral blood flow – modified by physical activity

•Increased BMI, WHR, and waist size associated with lower cerebral blood flow.•Waist size +1cm associated with same reduction in cerebral blood flow as +1year age.•Higher levels of physical activity shown to potentially modify these associations. This study examined the associations of body mass index (BMI), waist-to-hip ratio (WHR), waist circumference (WC), and physical activity (PA) with gray matter cerebral blood flow (CBFGM) in older adults. Cross-sectional data was used from the Irish Longitudinal Study on Ageing (n = 495, age 69.0 ±7.4 years, 52.1% female). Whole-brain CBFGM was quantified using arterial spin labeling MRI. Results from multivariable regression analysis revealed that an increase in BMI of 0.43 kg/m2, WHR of 0.01, or WC of 1.3 cm were associated with the same reduction in CBFGM as 1 year of advancing age. Participants overweight by BMI or with high WHR/WC reporting low/moderate PA had up to 3 ml/100g/min lower CBFGM (p ≤ .011); there was no significant reduction for those reporting high PA. Since PA could potentially moderate obesity/CBF associations, this may be a cost-effective and relatively easy way to help mitigate the negative impact of obesity in an older population, such as cerebral hypoperfusion, which is an early mechanism in vascular dementia and Alzheimer’s disease. [Display omitted]