Obesity Linked to Smaller Brain Volume

Fran Lowry

August 10, 2016

A big middle in middle age may mean a smaller brain, new research suggests.

An imaging study that compared white matter volume in obese and lean middle-aged individuals showed that those who were obese had significantly smaller white matter volumes than their lean counterparts.

Importantly, the authors note, this reduced white matter was not associated with a decrease in cognitive function.

"At this point, the implications of these findings are unclear; however, it is important to emphasize that despite significant differences in brain structure between people who are overweight or obese and their lean, age-matched counterparts, we found no significant differences in cognitive abilities between the two groups," lead author Lisa Ronan, MD, Department of Psychiatry, University of Cambridge, United Kingdom, told Medscape Medical News.

The study was published online July 27 in Neurobiology of Aging.

Accelerated Brain Aging?

Dr Ronan explained that the starting point for this analysis was the growing body of literature relating common markers of aging to those observed in obesity, suggesting that obesity may accelerate or advance the onset of brain aging.

The investigators examined the relationship between body mass index (BMI) and brain structure by analyzing MRIs of 473 adults aged 20 to 87 years.

They then contrasted white matter volume between persons who were lean (BMI, 18.5 - 25) and those who were overweight/obese (BMI > 25).

Participants were cognitively healthy. The mean age was 54 years, and the mean BMI was 26 kg/m2 (range, 18.5 - 45.5); 246 persons were lean, 150 were overweight, and 77 were obese.

Results indicated that cerebral white matter volume in overweight and obese individuals was associated with a greater degree of brain atrophy, with maximal effects in middle age corresponding to an estimated 10-year acceleration of brain aging.

A previous diagnosis of an elevation in cholesterol level was also associated with reduced white matter volume over and above the effects of age and BMI, suggesting that some common metabolic comorbidities associated with obesity may have a role in increasing susceptibility to neurodegeneration.

Exercise, income, or education did not affect the BMI-related effects on brain structure.

"The implication of these findings is as yet unclear and requires further analysis," said Dr Ronan.

"Although our results raise the possibility that being overweight or obese may increase the risk for developing age-related disorders linked to neurodegeneration, it is important to acknowledge that we found no such links in our current study, which included only adults who were cognitively healthy at the time of recruitment," she said.

Dr Ronan added that overall, the fact that the world's population is aging makes it critical to understand the full effects of increased body mass on health.

"As such, this study is part of a larger effort to understand the role obesity has on our health. It will be important for future studies to establish whether an increased BMI impacts on brain health, or whether brain changes somehow influence BMI," she said.

Dr Ronan cautioned that the study was exploratory, and as such, "without understanding the mechanism that underpins the observed association between BMI and brain structure, it is too early to give specific advice to patients on the basis of these results."

Noteworthy Study

Commenting on the findings for Medscape Medical News, Dilip V. Jeste, MD, Distinguished Professor of Psychiatry and Neurosciences and director, Sam and Rose Stein Institute for Research on Aging, University of California, San Diego, described the study as "noteworthy" and shows "that at population level, obesity is associated with degenerative changes in the brain white matter.

"Strikingly, the greatest effects of obesity in this report were seen in middle age and corresponded to an estimated acceleration of brain aging by 10 years.

"Notwithstanding the acknowledged study limitations, such as the use of BMI as a measure of adiposity, omission of extremely obese subjects due to scanner limitations, and the cross-sectional nature of the analysis, the take-home message is that planning for successful aging shouldn't start on the 65th birthday. To reduce the risk of accelerated brain aging, we need to maintain healthy body weight through diet and activity, beginning in young adulthood," said Dr Jeste.

The study was supported by the Bernard Wolfe Health Neuroscience Fund and the Wellcome Trust. Dr Ronan and Dr Jeste report no relevant financial relationships.

Neurobiol Aging. Published online July 27, 2016. Full text

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