Researchers examined data from the University of Michigan's 2018 National Poll on Healthy Aging (NPHA), a nationally-representative survey of adults ages 50 to 80. Overall, 44.3% of respondents said they were at least somewhat likely to develop dementia, and 4.2% said they were very likely to develop dementia.
Just 5.2% of survey participants said they had discussed dementia prevention with their doctor, the study also found.
Nonetheless, 31.6% said they took fish oil or omega-3 fatty acids to help lower their risk, and 39.2% took other vitamins or supplements. More than half of participants also believed doing crossword puzzles could help stave off dementia.
"Given repeated failures of disease-preventing or disease-modifying treatments for dementia, interest in treatment and prevention have shifted earlier in the disease process," study leader Dr. Donovan Maust of the University of Michigan in Ann Arbor and colleagues write in JAMA Neurology.
The authors point out that overestimating one's own risk combined with an embrace of ineffective preventive measures could lead to a lot of wasted spending, even if effective preventive treatments are discovered one day.
"Adults in middle age may not accurately estimate their risk of developing dementia, which could lead to both overuse and underuse if preclinical dementia treatments become available," Maust and colleagues write.
About 1.6% of the U.S. population had Alzheimer's disease and other forms of dementia as of 2014, according to the U.S. Centers for Disease Control and Prevention. By 2060, this will more than double to 3.3% of the population.
Advancing age is the biggest risk factor for dementia, along with family history, being African-American or Hispanic, or having poor cardiovascular health or a traumatic brain injury, according to the CDC.
Normal age-related memory changes can include things like occasionally losing car keys or forgetting the name of an acquaintance, but this might not necessarily lead to dementia. With dementia, people might use unusual words to refer to familiar objects or forget the name of a close friend or loved one.
In the current study, black respondents were 49% less likely than white people to believe they might develop dementia.
And compared to people who rated their physical health as excellent, respondents who rated it as good were 49% more likely to think they might develop dementia and those who rated their health fair or poor were 46% more likely to think they might develop dementia.
Compared to people who rated their mental health as excellent, those who rated it as fair or poor were 2.5 times more likely to think they might develop dementia.
People were more likely to speak to their doctor about dementia if they thought they had a higher likelihood of developing it, the study also found.
The researchers lacked data on whether people actually had signs or symptoms of dementia, or medical records to indicate whether they had any chronic health conditions that might increased their risk.
"While managing chronic medical conditions, such as diabetes or cardiovascular disease, could reduce dementia risk, few respondents appear to have discussed this with their physician," the study team writes. "Physicians should emphasize current evidence-based strategies of managing lifestyle and chronic medical conditions to reduce the risk of dementia."