Objective To examine the association of body mass index (BMI) and waist-to-hip ratio (WHR) with brain volume.
Methods We used cross-sectional data from the UK Biobank study (n = 9,652, age 55.4 ± 7.5 years, 47.9% men). Measures included BMI, WHR, and total fat mass as ascertained from bioimpedance. Brain images were produced with structural MRI.
Results After adjustment for a range of covariates, higher levels of all obesity measures were related to lower gray matter volume: BMI per 1 SD (β coefficient −4,113, 95% confidence interval [CI] −4,862 to −3,364), WHR (β coefficient −4,272, 95% CI −5,280 to −3,264), and fat mass (β coefficient −4,590, 95% CI −5,386 to −3,793). The combination of overall obesity (BMI ≥30 kg/m2) and central obesity (WHR >0.85 for women, >0.90 for men) was associated with the lowest gray matter compared with that in lean adults. In hypothesis-free testing with a Bonferroni correction, obesity was also related to various regional brain volumes, including caudate, putamen, pallidum, and nucleus accumbens. No associations between obesity and white matter were apparent.
Conclusion The combination of heightened BMI and WHR may be an important risk factor for gray matter atrophy.