August 8, 2005
Elevated levels of insulin, the hormone that regulates blood sugar and is vital for normal body function, may lead to inflammation and play a role in the onset of Alzheimer's, researchers report. Excess insulin may also be associated with high levels of beta amyloid, the toxic protein that builds up in the brains of those with the disease. Scientists hope that better understanding of the role of insulin in the development of Alzheimer's may lead to new therapies to control or even prevent the mind-ravaging disease.
Produced by the pancreas, insulin regulates the uptake of blood sugar (glucose) by muscle and fat and is vital for normal body functioning. People who have diabetes must regularly inject themselves with a drug form of insulin because their bodies either do not make enough of the hormone or do not respond to it properly. In addition to those with diabetes, many people who are overweight or have high blood pressure or heart disease do not process insulin properly.
In the current study, scientists at the University of Washington in Seattle raised blood insulin levels moderately in 16 healthy adults aged 55 to 81 while maintaining their blood sugar levels in a normal range. The researchers then measured levels of proteins in the blood and the cerebrospinal fluid (CSF), the fluid that bathes the spinal cord and brain.
The doctors found that elevated levels of insulin led to an increase in proteins associated with inflammation. Mounting evidence suggests that inflammation damages blood vessels, leading to cardiovascular disease. Inflammation may also contribute to the onset of Alzheimer's disease.
High insulin was also linked to high levels of beta amyloid. The buildup of toxic forms of beta amyloid in the brain is thought by many experts to play a key role in the development of Alzheimer's.
Millions of Americans have high insulin levels because of diabetes or as a result of a related metabolic condition. People who are overweight or have heart disease or high blood pressure also tend to produce greater amounts of insulin. As our population ages, more people are expected to suffer from these ailments, as well as from Alzheimer's disease. The researchers write, "the Alzheimer's-insulin link may lead to novel and more effective strategies for treating, delaying, or even preventing this challenging disease."
Numerous studies have shown possible links between diabetes and heart disease and the onset of Alzheimer's disease. Other studies support the role of losing weight and maintaining a heart-healthy lifestyle in preventing the onset of the illness. Because diabetes, heart disease, and obesity are so common in our society, greater understanding of these ailments and insulin's role in the development of Alzheimer's is critical.
The study was posted online in the August Archives of Neurology, a research journal from the American Medical Association. The article will appear in the October print version of the journal. For more on the causes and prevention of Alzheimer's disease, visit www.ALZinfo.org.
Source: Archives of Neurology, August 8, 2005:62; 1-6, special on-line publication.