That news comes from a Swedish study of more than 2,200 men followed for up to 35 years, starting at age 50.
"Our results suggest a link between insulin problems and the origins of Alzheimer's disease and emphasize the importance of insulin in normal brain function," Elina Ronnemaa, MD, of Sweden's Uppsala University, says in a news release. "It's possible that insulin problems damage blood vessels in the brain, which leads to memory problems and Alzheimer's disease, but more research is needed to identify the exact mechanisms."
When the Swedish study started, the men took fasting glucose tests to show how well their body used insulin, a hormone that controls blood sugar.
Men who had a weaker insulin response to that test were 31% more likely to be diagnosed with Alzheimer's disease later in life, regardless of other factors such as age, BMI (body mass index), and education level.
That pattern applied to men with and without diabetes; it was strongest among men without the Alzheimer's-related APOE4 gene variation.
The findings, published in today's online edition of Neurology, follow a study released in 2007 linking poorly controlled diabetes to Alzheimer's disease and other research on the link between diabetes and Alzheimer's disease.
However, there are other risk factors for Alzheimer's disease, and as the Swedish researchers point out, it will take more work to put together all the pieces of the puzzle.