Insulin resistance is associated with diabetes, obesity, hypertension, and cancer. More mysterious is how insulin affects the brain.
In the October issue of Archives of Neurology, Suzanne Craft at the Veterans Affairs Puget Sound Health Care System in Seattle and colleagues demonstrate that an abnormally high level of insulin triggers the release of beta-amyloid protein and likely increases the risk of Alzheimer’s disease.
People with insulin resistance have a higher risk of Alzheimer’s disease, but why that is true has not been clear. To find out, Craft’s team gave healthy volunteers either saline or insulin intravenously for 105 minutes and then took blood and cerebral spinal fluid samples.
During insulin infusions, researchers recreated the physiological impact of insulin resistance by also giving volunteers dextrose so the extra insulin would not deplete their blood sugar.
The amount of beta-amyloid was higher in both the cerebral spinal fluid and plasma after treatment with insulin, as were inflammatory proteins that are also associated with increased risk of Alzheimer’s disease. The effect was exaggerated in volunteers who had a higher body mass index or who were older.
Although the study does not show what would happen in people who are exposed to excess insulin for years, it does indicate that elevated insulin can induce expression of proteins associated with brain degeneration.
“The good news is that it also suggests that treating insulin resistance might reduce the risk of Alzheimer’s disease or delay its onset,” Craft says.