The first clue is high blood sugar, not just diabetes, may increase the risk of getting the disease.
Researchers from the University of Washington studied more than 2,000 people and found those with higher glucose levels over five years had an 18 percent greater risk of dementia.
"The mechanism question is fascinating, and we don't know why," said Paul Crane, Associate Professor of Internal Medicine at the University of Washington.
High systolic blood pressure may also be a factor.
Another study found middle-aged people with high systolic blood pressure were more likely to have biomarkers of Alzheimer's disease in their spinal fluid. Every 10-point rise in pressure caused the average level of a protein, called tau, to increase.
Another clue to Alzheimer's disease may be how you walk.
Mayo Clinic scientists found a slowed walking pace and shortened stride were associated with a decline in mental skills and memory.
Depression is also linked, especially if you have both depression and diabetes.
"That dramatically increases your risk by over two-fold," Wayne Katon, Professor and Vice Chair of the Department of Psychiatry at the University of Washington Medical School.