Medical science has failed to prove that any treatment, therapy or brain exercise can help prevent dementias such as Alzheimer's disease, an extensive new review has concluded.

No medications, over-the-counter remedies or brain training programs have been proven in solid clinical trials to ward off dementia, researchers with the Minnesota Evidence-Based Practice Center in Minneapolis stated after reviewing dozens of previously published studies.

"The upshot is there isn't a magic bullet," said review co-author Mary Butler, co-director of the center and an assistant professor with the University of Minnesota School of Public Health.

The best evidence the investigators found indicates that healthy living is a person's best defense against dementia, Butler said. That means eat right, exercise, treat health problems such as high blood pressure, and remain socially active.

"Of those interventions we were able to find that were tested, the few that showed potential for benefit or even hinting at benefit are really very similar to the kinds of public health messages we put out there in general about healthy aging," Butler said.

The researchers conducted four side-by-side evidence reviews to test different categories of proposed therapies and treatments for Alzheimer's:

•    Physical activity. Low-strength evidence from 16 trials showed that combining different types of activity -- exercise, diet and cognitive training -- might improve performance on brain tests.

•    Prescription drugs. No medications appeared to protect the brain in data from 51 trials. The drugs studied included those specifically for dementia as well as drugs to treat other health problems of aging, such as diabetes, high blood pressure, elevated cholesterol and ebbing hormone levels.

•     Vitamins and supplements. There's no evidence from 38 trials that any over-the-counter tablets or pills can prevent dementia or Alzheimer's disease. This included omega-3 fatty acids, ginkgo biloba and vitamins B, C, D and E.

•     Cognitive training. Brain exercises did not ward off dementia in 11 clinical trials.

"There is some moderate evidence that cognitive engagement brings some benefits, but those benefits are local," Butler said. "If we train on memory, our memory might improve. If we train on processing, our processing speed might improve. But there isn't any good evidence to directly link that to changes in how many people develop dementia."

Dean Hartley, director of science initiatives at the Alzheimer's Association, said people shouldn't be discouraged by this review. It doesn't rule out any possible treatments for dementia -- it just notes that science hasn't proven that any of them work.

"What we need is more research, and that's what this brings to light," Hartley said.

Further, it's a good sign that some evidence indicates that lifestyle changes like exercise and a healthy diet can help with dementia, Hartley continued.

"We can all be doing these now because they aren't things that are going to hurt us, and will generalize to our health," he said. "A healthy heart is a healthy brain. We will see that benefit to the brain."

Alzheimer's researcher Dr. Luca Giliberto also sees the evidence review as positive, but from a different angle: He hopes the review will shake up the field of research.

"Finally, somebody had the guts to state the fact that we don't understand what's going on with dementia and Alzheimer's," said Giliberto, an assistant professor with the Feinstein Institute for Medical Research in Manhasset, N.Y. "There's nothing we currently are able to do to stop Alzheimer's pathology." Researchers need to return to the basics and focus on figuring out why people develop Alzheimer's before they start testing cures, he said.

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