Exercise may protect brain health by keeping insulin, BMI levels low

• Existing studies show that exercise helps protect brain cells through mechanisms that researchers do not yet fully understand.

• Researchers know that exercise increases brain glucose metabolism, which correlates with improved brain function.

• Studies show that exercise affects insulin resistance and has a complex relationship with body mass index (BMI) levels.

• A new study suggests that exercise plays a role in maintaining insulin and BMI levels, which may help stave off dementia by protecting gray matter volume in the brain.

A new study investigates the mechanisms involved in the relationship between exercise and brain health.

Previous research had shown that larger gray matter volume can help protect against dementia by improving brain function.

The new study shows that insulin resistance and BMI mediate the relationship between larger and smaller brain gray matter volumes (the part of the brain involved in processing information).

The research is published in the April 2022 online issue of Neurology, the medical journal of the American Academy of Neurology.

The corresponding author of the study was Dr. Geraldine Poisnel, of the Inserm Regional Research Center, in Caen, Normandy, France.

Studying glucose metabolism and brain volume

The study involved 134 people with an average age of 69 who had no memory problems. The participants filled out a physical activity survey covering the past 12 months. They also had brain scans to measure glucose metabolism and brain volume.

The metabolism of glucose in the brain provides fuel for the brain by generating adenosine 5′-triphosphate (ATP) — a key molecule for maintaining the health of neurons and other cells. ATP is also key for generating neurotransmitters. Reduced glucose metabolism in the brain can be seen in people with dementia.

Gray matter development peaks at age 2–3 years. It begins to decrease afterward in some areas of the brain, but the density of the gray matter increases. From an evolutionary perspective, the higher processing ability of the human brain and its development are due to this increase in density.

In some studies, larger total brain volume, estimated by magnetic resonance imaging (MRI), has a weak correlation with higher intelligence in men and a very weak correlation in women with the ability to do well in intelligence tests.

In contrast, brain tissue deterioration and loss of volume is a significant contributor to lower cognitive ability later in life.

In the new study, researchers included 134 people with an average age of 69 who had no memory problems. The participants filled out a physical activity survey covering the past 12 months. They also had brain scans to measure glucose metabolism and brain volume.

Body mass index and insulin levels affect brain health

In the new study, researchers gathered formation on cardiovascular risk factors including BMI and insulin levels, as well as cholesterol, blood pressure, and other factors.

The researchers examined the relationship between insulin and cardiovascular disease. The metabolic abnormalities that insulin causes raise the risk of cardiovascular complications, which in turn affect brain function.

Researchers found that insulin and BMI levels did not affect the metabolism of glucose in the brain.

Alzheimer’s disease marker not affected

The research demonstrated that the amount of amyloid plaque in the brain that contributes to Alzheimer’s Disease was not affected by exercise.

Medical News Today contacted Dr. Raeanne Moore, associate adjunct professor of psychiatry at UCSD in La Jolla, CA.

Dr. Moore, who was not involved in the study, was asked about the study results. She shared with MNT:

“This study adds to the growing body of research on the positive benefits of staying active on brain health, especially as we age.”

“[T]here is an urgent need to identify markers of cognitive decline,” added Dr. Moore. “Decreasing insulin levels and losing weight are modifiable factors that can be improved with a healthy diet and exercise.”

She added, “It was not surprising that higher physical activity was not associated with how much amyloid plaque people had in their brains. There is growing evidence that vascular risk factors on cognitive function are mediated by the amount of tau pathology in the brain and not an amyloid burden.”

Takeaway

MNT also spoke with Dr. Sheldon Zablow, assistant professor of medicine at University of California San Diego Medical School in La Jolla, CA. Dr. Zablow shared his comments about this study:

“Exercise has often been called food for the brain with many studies showing the benefit of exercise for improving brain health and reducing the risk of dementia.”

“This current research study states that physical activity improves cognitive brain function by reducing BMI and improving insulin metabolism. Improvement in weight control can limit the rate of brain volume loss, a known risk factor for dementia.”

“This study will help physicians reinforce the importance of regular exercise in reducing BMI as a low-cost means of limiting cognitive decline.”

– Dr. Zablow

Dr. Moore’s final remarks were, “The literature clearly demonstrates that cardiovascular risk factors are associated with cognitive decline and risk for Alzheimer’s disease and related dementias.”

“Studies investigating subtle brain changes prior to the development of dementia are critical to optimizing brain health and staving off cognitive decline.”

Study strengths and limitations

“Strengths of this study include a sample of cognitively normal older adults and the use of multimodal imaging methods to explore the role of CVD risk factors in the association between physical activity and neuroimaging biomarkers,” said Dr. Moore.

“[T]his methodology can move the field forward by helping to identify important markers of risk for cognitive decline.”

“A limitation to the study was the use of a self-report of physical activity […] which the authors acknowledged as a limitation. Self-report of physical activity is prone to retrospective recall bias, and objective tools to measure physical activity, such as fitness trackers, are more accurate.”

“These findings that insulin and BMI fully mediated the relationship between physical activity and whole-brain gray matter volume — and specifically hippocampal gray matter volume — provide further evidence that targeting these modifiable CVD risk factors could improve brain health.”

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