People with diabetes lack the ability to make or use insulin, a hormone that helps the body to maintain healthy levels of glucose, or blood sugar. Now researchers have found that problems using insulin in the brain may contribute to the memory problems of Alzheimer’s disease.
The findings add to a growing body of research linking diabetes with Alzheimer’s and other forms of dementia. Better understanding of the link between diabetes and Alzheimer’s could lead to better treatments for the devastating disease, the researchers say.
The researchers, from the University of Pennsylvania’s Perelman School of Medicine in Philadelphia, found abnormalities in the way people with Alzheimer’s process insulin in the brain. Insulin is critical for the functioning of tissues throughout the body, including in the brain. None of the study subjects had diabetes, yet their brains showed signs of insulin resistance, or an inability to take up and use insulin properly. The study appeared online in the Journal of Clinical Investigation.
"Our research clearly shows that the brain's ability to respond to insulin, which is important for normal brain function, is going offline at some point,” said Dr. Steven E. Arnold, senior author and a professor of Psychiatry and Neurology at the University of Pennsylvania. “We believe that brain insulin resistance may be an important contributor to the cognitive decline associated with Alzheimer's disease."
He noted that if diabetes drugs that prevent insulin resistance or that resensitize cells to insulin could be effectively delivered to the brain, “we may be able to slow down, prevent or perhaps even improve cognitive decline.”
Three insulin-sensitizing medicines are already approved by the Food and Drug Administration to treat diabetes. All readily cross the blood-brain barrier and may have therapeutic potential to correct insulin resistance in Alzheimer's disease and mild cognitive impairment, or MCI, a serious form of memory loss that often precedes Alzheimer’s.
"Clinical trials would need to be conducted to determine the impact the drugs have on Alzheimer's disease and MCI in non-diabetic patients," said Dr. Arnold.
The findings add to a growing body of evidence showing a link between diabetes and Alzheimer’s disease. People with diabetes are at 50 percent increased risk of developing Alzheimer’s disease. Diabetes damages blood vessels throughout the body, including in the brain, and is a cause of Vascular Dementia, which may also contribute to memory loss of Alzheimer’s.
Last year, researchers noted in a small pilot study that squirting insulin deep into the nose, where it travels to the brain, might help to ward off Alzheimer’s. Those who got the insulin either improved slightly or showed no deterioration in memory and thinking skills. [See the ALZinfo.org story, “Insulin Squirt Helps People With Early Alzheimer’s,” at http://www.alzinfo.org/09/articles/prevention-and-wellness/insulin-squirt-helps-people-early-alzheimers.] A larger study is under way.
It is important to note, however, that having diabetes does not mean that you will develop Alzheimer's as you age. Rather, diabetes may put you at increased risk for developing these conditions. Similarly, many people who develop Alzheimer's do not have diabetes.
But preventing diabetes in the first place may be important for long-term brain health, this and other studies suggest. Keeping weight down, getting regular exercise and eating a diet rich in fresh fruits and vegetables may all help to keep diabetes at bay – and in the process may help to stem the memory loss of Alzheimer’s.
Source: Konrad Talbot, Hoau-Yan Wang, Hala Kazi, et al: “Demonstrated brain insulin resistance in Alzheimer’s disease patients is associated with IGF-1 resistance, IRS-1 dysregulation, and cognitive decline.” The Journal of Clinical Investigation, March 2012.