How Diabetes Affects Your Brain

Medically Reviewed By William C. Lloyd III, MD, FACS

Diabetes can have an impact on your whole body. Your brain is no exception. Recent studies have linked type 2 diabetes to a slowdown in mental functioning and an increased risk of Alzheimer’s disease. The chance of brain complications is just one more reason to keep your diabetes under control.

Diabetes on the Brain

Scientists are still unsure exactly how type 2 diabetes might affect the brain. However, multiple factors are probably involved.

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“High blood sugar may directly affect either nerve cells or support cells in the nervous system,” says Alan Jacobson, M.D., emeritus professor of psychiatry at Harvard Medical School. “It can also lead to damage in both large and small blood vessels.” This, in turn, reduces the amount of oxygen reaching the brain. Plus, it increases the risk of having a stroke, which can kill brain cells.

In addition, type 2 diabetes usually begins with insulin resistance, in which fat, muscle, and liver cells aren’t able to use insulin effectively. At first, the pancreas responds by pumping out more insulin. The same enzyme that breaks down insulin also breaks down a protein called beta-amyloid, which builds up abnormally in the brains of people with Alzheimer’s disease. With so much of the enzyme at work breaking down insulin, beta-amyloid might have more chance to accumulate.

Effect on Mental Processing

Research has linked type 2 diabetes to a decline in mental functioning. One study looked at which mental abilities were hardest hit in middle-aged and older adults with diabetes. The results pointed to neurocognitive speed and executive functioning. “These are thought to be major components of cognitive health,” says researcher Roger Dixon, Ph.D., a psychology professor at the University of Alberta.

Neurocognitive speed refers to how quickly and accurately you respond to situations. It’s a useful gauge of overall brain health. Executive functioning refers to the planning, control, and monitoring of your own mental activities. “It’s crucial to success in everyday life,” says Dr. Dixon.

The good news is that the deficits seen in this study were mild. And it’s possible they might be preventable. Dr. Dixon says, “By controlling diabetes through medication and lifestyle changes, people may be able to control or limit its effects on the health of their brains.”

Higher Risk for Alzheimer’s Disease

Other research has linked type 2 diabetes to Alzheimer’s disease. One study of Swedish twins found an increased risk of Alzheimer’s later in life among people who had diabetes by middle age. The effect wasn’t as strong in those who got diabetes after age 65. “It seems that the longer you have diabetes, the greater the Alzheimer’s risk,” says researcher Margaret Gatz, Ph.D., a psychology professor at the University of Southern California.

Studies have found a similar link between midlife high blood pressure or obesity and later Alzheimer’s. With blood pressure, at least, “controlling it brings the risk back down,” Dr. Gatz says. The implication: Getting healthier doesn’t just benefit you today. It may also help protect your brain for decades in the future.

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  1. “Exploring Effects of Type 2 Diabetes on Cognitive Functioning in Older Adults.” S.E. Yeung et al. Neuropsychology, 2009, vol. 23, pp. 1-9. 

  2. “Mid- and Late-Life Diabetes in Relation to the Risk of Dementia: A Population-Based Twin Study.” W. Xu et al. Diabetes, 2009, vol. 58, pp. 71-77. 
  3. Alan Jacobson, MD; Emeritus Professor of Psychiatry, Harvard Medical School; Chief Research Officer; Winthrop-University Hospital; Mineola, NY. Interview. 

  4. Margaret Gatz, Ph.D.; Professor of Psychology, Gerontology and Preventive Medicine, University fo Southern California; Los Angeles, CA. Interview. 

  5. Roger Dixon, PhD; Canada Research Chair in Cognition and Aging, Professor of Psychology. University of Alberta; Edmonton, AB, Canada. Interview.
  6. National Institute of Diabetes and Digestive and Kidney Diseases.
Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jul 30
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