Overweight and Obesity Linked to Lower Brain Volume

Caroline Cassels

August 28, 2009

August 28, 2009 — Overweight and obese individuals have significantly lower brain volume than their normal-weight counterparts, a finding researchers say puts these individuals at much greater risk for dementia, including Alzheimer's disease.

Results from a new imaging study reveal that, on average, obese subjects had 8% lower brain volume than normal-weight subjects and overweight subjects had 4% lower brain volume.

"That's a big loss of tissue and it depletes your cognitive reserves, putting you at much greater risk of Alzheimer's and other diseases that attack the brain," principal investigator Paul M. Thompson, PhD, from the Lab of Neuro Imaging, UCLA School of Medicine, in Los Angeles, California, said in a statement.

The study was published online August 6 in Human Brain Mapping.

Worldwide Problem

It is well known that obesity increases the risk for cardiovascular illness, including diabetes, hypertension, and stroke, all of which increase the risk for cognitive decline and dementia. However, the authors point out, it is not known whether these factors, specifically obesity and type 2 diabetes, are associated with specific patterns of brain atrophy.

The authors note that there are currently more than 1 billion overweight and 300 million obese individuals worldwide. In addition, 40% of men and 45% of women older than 70 years are either obese or have type 2 diabetes.

To examine gray- and white-matter volume differences in elderly subjects, the researchers used tensor-based morphometry to examine gray- and white-matter volume differences in 94 elderly subjects who remained cognitively normal for a minimum of 5 years after their scan.

Researchers used participants in the Cardiovascular Health Study (CHS) Cognition Study, a continuation of the CHS Dementia Study, which began in 2002/2003, to determine the incidence of dementia and mild cognitive impairment in a population of normal and mild cognitive-impairment-subjects identified in 1998/1999.

To define weight categories, they used the body mass index (BMI). Normal weight was defined as a BMI of 18.5 to 25.0 kg/m2; overweight was defined as a BMI of 25 to 30 kg/m2, and obese was defined as a BMI greater than 30 kg/m2. Subjects were classified as having type 2 diabetes if they met any 1 of the standard criteria for the disease.

Of the total study sample, 29 participants were normal weight, 51 were overweight, and 14 were obese.

Aging Effect

Multiple regression analyses revealed that BMI was negatively correlated with brain atrophy, and that type 2 diabetes and fasting plasma insulin levels were not. Specifically, the investigators found that a higher level of body tissue was associated with brain-tissue loss in the frontal and temporal lobes, the anterior cingulate gyrus, the hippocampus, and the basal ganglia.

Overweight individuals had brain loss in the basal ganglia, the corona radiate, and the parietal lobe. The authors report that negative correlations between body-tissue fat and brain structure were strongest in obese people, but were also seen in overweight people.

"The brains of obese people looked 16 years older than the brains of those who were lean, and in overweight people they looked 8 years older," said Dr. Thompson.

"It seems that, along with increased risk for health problems such as such type 2 diabetes and heart disease, obesity is bad for your brain. We have linked it to the shrinkage of brain areas that are targeted by Alzheimer's disease," study investigator Cyrus A. Raji, MD, from the University of Pittsburgh School of Medicine in Pennsylvania, said in a statement. "But that could mean that exercising, eating right, and keeping weight under control can maintain brain health with aging and potentially lower the risk for Alzheimer's and other dementias."

The researchers have disclosed no relevant financial relationships.

Hum Brain Mapp. Published online before print August 6, 2009. Abstract


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