Impaired memory and thinking are the most common symptoms associated with a dementia diagnosis. "You can have many of these other precursors but not have any cognitive symptoms," said Timothy Chang, an associate professor of neurology at UCLA. Of course, experts caution that having early symptoms linked to an increased risk of Alzheimer's does not mean you'll necessarily develop dementia, and about 45 percent of dementia cases are preventable with lifestyle changes. It's both a risk factor for dementia and a potential early warning sign that can appear about a decade before cognitive symptoms begin. How to reduce your dementia riskThere's a genetic component to dementia risk, but there are also many ways we can reduce our risk.