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Many older people try to keep their brains sharp by exercising, staying mentally active and watching their diets. Yesterday, a panel convened by the National Institutes of Health warned the public that it is not clear that any of these measures can prevent Alzheimer's disease or other forms of mental decline.

NPR's Jon Hamilton says many scientists are still optimistic about prevention, partly because they're also considering research done on animals.

JON HAMILTON: At about the time the panel was releasing its report, a 78-year-old senator was doing something he hopes is good for his brain.

Unidentified Man: And here comes Senator Richard Lugar, 29 times in a row.

(Soundbite of cheering and applause)

Unidentified Man: Running strong after 29 years.

HAMILTON: Lugar was competing in an annual charity race a few miles from Capitol Hill. He's been a runner since grade school and thinks exercise helps him remember a lot of stuff.

Senator RICHARD LUGAR (Republican, Indiana): The names and places of thousands of people and events that I bring up frequently in the course of debate. It's very helpful to have that kind of historical knowledge of my constituency, as well as of the world.

HAMILTON: The panel convened by the NIH wasn't so sure that's why people like Lugar remain sharp into their 70's and 80's. And they wanted to make sure the public wasn't being misled about the benefits of this or any other strategy for preventing Alzheimer's. So the panel looked only at studies in humans, and they found some studies of exercise in people have found a benefit, while others haven't.

Arthur Kramer, a neuroscientist from the University of Illinois, wasn't on the panel, though he was invited to speak to the group. He says the panel is right to be cautious. But he says there are reasons researchers talk about the potential of exercise.

Professor ARTHUR KRAMER (Neuroscientist, University of Illinois): The benefits tend to be on the order of a 20 to 30 percent reduction in being diagnosed with Alzheimer's disease and other such diseases. Then again, this isn't universal, but this is found in increasing number of studies.

HAMILTON: Kramer says researchers also tend to consider studies that show what exercise does for animals.

Prof. KRAMER: There are improvements in the chemistry of the brain, in terms of the molecules that protect the brain, increases in the number of connections between neurons, and even the birth of new neurons in one region of the brain that supports memory.

HAMILTON: Mental exercise is another strategy that seems like a good idea to many Alzheimer's researchers. After all, it appears to increase connections in the brain and make the brain more resilient - in animals, and perhaps in people.

But Neil Buckholtz from the National Institute on Aging says the panel would need a lot more than that to recommend a specific activity to the public.

Dr. NEIL BUCKHOLTZ (National Institute on Aging): Doing crossword puzzles or Sudoku, those kinds of things. They're interesting, but the evidence is not available at this point that they actually have an effect.

HAMILTON: The panel seemed most skeptical about studies of drugs, diets and nutritional supplements. Members found some evidence of benefit from Omega-3 fatty acids, like those in fish. But it found no convincing studies in people that anti-oxidants like Vitamin E could make a difference.

Martha Clare Morris is less skeptical. She's a nutritional epidemiologist at Rush University Medical School in Chicago, who was invited to speak to the panel. Morris says there is good evidence that some anti-oxidants work in animals.

Dr. MARTHA CLARE MORRIS (Nutritional Epidemiologist, Rush University Medical School): There's a very broad base of animal models to show that Vitamin E protects the brain from neuron loss, from DNA damage, from oxidative damage.

HAMILTON: Panel members say they'll consider changing their position on Vitamin E and other popular prevention strategies when researchers show they work in people.

Jon Hamilton, NPR News.

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