Greater body mass index (BMI) and weight circumference are strongly associated with cortical thinning and reduced gray matter, as seen on magnetic resonance imaging (MRI), according to study results published in Neurology.

Previous studies examining measures of obesity and brain structure have mainly focused on markers of cerebral small vessel disease and volumetric measures of brain structure, and few epidemiologic studies have examined the association of obesity with cortical thickness. The goal of this study was to examine the associations between obesity measure — including BMI, weight circumference, and waist-to-hip ratio — in middle to early old age with later life markers of brain aging on MRI scans.

The researchers analyzed data from the Northern Manhattan Study (NOMAS), an ongoing longitudinal cohort study of older adults with no history of clinical stroke. Additionally, they examined how associations varied by age, sex, and race/ethnicity. The primary outcomes of interest included total cerebral volume, cortical thickness, white matter hyperintensity volume, and subclinical brain infarcts.

The study included 1289 participants (mean age 64 years; 60% women; 66% Hispanic/Latino).

Greater BMI and greater weight circumference were associated with smaller total cerebral volume, and the strength of these associations remained consistent after adjustment for vascular risk factors. Lower adiponectin levels were associated with smaller cerebral volumes; relative to the first quartile of adiponectin concentration, those with adiponectin concentrations in the 2nd quartile exhibited greater total cerebral volume (β=0.063; 95% CI, 0.001, 0.125).

In fully adjusted models, greater BMI was significantly associated with thinner cortices (β=-0.086; 95% CI, -0.145 to -0.026), as was greater weight circumference (β=-0.103; 95% CI, -0.169 to -0.037). Compared with those with BMI <25, obese participants (BMI ≥30) exhibited smaller cortical thickness (β=−0.207; 95% CI, -0.374 to −0.041). Associations between cortical thickness and other obesity markers did not reach statistical significance in adjusted models.

Greater weight circumference was related to thinner cortices in adults aged <65 years (β=-0.168; 95% CI, -0.243 to -0.093) but not in older participants.

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The researchers noted several limitations of the study, including the cross-sectional design, possible survival bias because of the aging cohort, missing data, as well as additional residual and unmeasured confounders.

“Overall, this is among the largest studies to examine several measures of obesity with MRI metrics of brain aging and also represents data from an urban race-ethnic diverse population,” the researchers concluded. They emphasize that, “greater BMI, obesity, and greater weight circumference are related to reduced gray matter in this sample.”

Reference

Caunca MR, Gardener H, Simonetto M, et al. Measures of obesity are associated with MRI markers of brain aging: The Northern Manhattan Study. (published online July 24, 2019). Neurology. doi:10.1212/WNL.0000000000007966.