Study examines effect of obesity on the brain at various stages of cognitive health

Multimodal neuroimaging showed varying relationships between indices of obesity and the brain at three different diagnostic stages, including cognitively healthy, mild cognitive impairment and Alzheimer’s disease dementia.

The results were published in Journal of Alzheimer’s Disease Reports.

“Research has shown conflicting evidence surrounding the effects of obesity on the brain across various stages of life and disease,” the researchers wrote. “Given the uncertainty, a characterization of the neural phenotype associated with obesity that can be stratified using cognitive status would be extremely valuable in the management of patient body-fat composition to reduce damage to the brain in clinical settings.”

Manmohi D. Dake, a third-year PhD student in the department of neuroscience at the University of Sheffield in the United Kingdom, and colleagues performed multimodal neuroimaging to “clarify” the link between obesity and MRI-defined neural properties in patients at various stages of cognitive impairment due to AD.

The researchers obtained scans from 47 patients diagnosed with mild AD dementia, 68 patients with mild cognitive impairment and 57 cognitively healthy individuals. They assessed voxel-wise correlations between maps of gray matter volume, white matter integrity and cerebral blood flow and global/visceral obesity.

Dake and colleagues observed no “significant group differences” in age, total intracranial volume and waist circumference. Patients defined as cognitively healthy “ranked the highest” regarding measurements of years of education, Mini-Mental Status Examination, BMI and gray matter volume, while patients with mild cognitive impairment and AD dementia, respectively, ranked lower than cognitively healthy individuals.

Study results demonstrated negative correlations between obesity and white matter integrity, as well as cerebral blood flow, in temporoparietal regions among cognitively healthy individuals. Among patients with mild cognitive impairment, Dake and colleagues observed negative correlations in frontal, temporal and brainstem regions. They also saw a positive correlation between obesity and gray matter volume around the right temporoparietal junction among patients with mild dementia.

The results suggested that “being on the higher end of the obesity spectrum may be detrimental to brain structure,” according to Dake and colleagues.

Additionally, the findings “are of central importance” for classifying and managing patients with AD and, more generally, those referred for a neurological exam, they noted.

“Although obesity is mentioned among the risk factors for AD, its exact effects on the brain are still undetermined. These findings highlight multicomponent mechanisms associated with obesity, involving diagnosis-dependent properties of [gray matter volume], [white matter integrity] and [cerebral blood flow]," the researchers wrote. "This evidence emphasizes the urgent need to introduce early interventions that advocate lifestyle assessment and remediation across the lifespan. It also highlights the importance of primary prevention strategies based on modulation of lifestyle factors such as obesity in midlife as an effective strategy to achieve a reduction of AD-related dementia with advancing age.”