Many older American adults may inaccurately estimate their chances for developing dementia and do useless things to prevent it, new research suggests.

Almost half of adults surveyed believed they were likely to develop dementia. The results suggest many didn’t understand the connection between physical health and brain health and how racial differences can affect dementia risk.

Substantial numbers of people who rated their health as fair or poor thought their dementia chances were low. At the same time, many who said they were in excellent health said they were likely to develop the memory robbing disease.

Many said they tried at least one of four unproven memory-protecting methods, including taking supplements like fish oil and ginkgo. The most popular strategy was doing crossword puzzles. Mental stimulation is thought to help, but there’s stronger evidence for more challenging activities than puzzles — things like playing chess, taking a class, reading about unfamiliar topics, said Keith Fargo, who oversees research and outreach programs at the Alzheimer’s Association. He was not involved in the study.

Research has shown that regular exercise, a good diet, limiting alcohol and not smoking make dementia less likely. Supplements have not been shown to help.

“We really haven’t done a good job of getting the word out that there really are things you can do to lower your risk,” said Dr. Donovan Maust, the study’s lead author and a geriatric psychiatrist at the University of Michigan.

The study was published online Friday in JAMA Neurology. It’s based on a nationally representative health survey of 1,000 adults aged 50 to 64.

The survey asked people to assess their likelihood of developing dementia and whether they had ever discussed ways to prevent it with their doctor. Few people said they had, regardless of their self-rated risk for dementia.

The results raise concerns because doctors can help people manage conditions such as high blood pressure and diabetes that have been linked with dementia risk, Maust, said.