Fish oil, exercise and doing puzzles may all be good for the brain, but there is no strong evidence that any of these can prevent Alzheimer's disease, an expert panel concluded.
Nor can any other supplements, drugs or social interaction, the independent panel meeting at the National Institutes of Health outside Washington concluded.
The group of experts looked at the dozens of studies that have suggested ways to prevent Alzheimer's - a devastating and incurable breakdown of the brain - and found none were strong enough to constitute proof.
"We wish we could tell people that taking a pill or doing a puzzle every day would prevent this terrible disease, but current evidence doesn't support this," said Dr Martha Daviglus of Northwestern University in Chicago, who chaired the panel.
Most of the studies that have been done show associations, but not cause and effect, Daviglus said.
Specialists discuss dilema
"These associations are examples of the classic chicken or the egg quandary. Are people able to stay mentally sharp over time because they are physically active and socially engaged, or are they simply more likely to stay physically active and socially engaged because they are mentally sharp?" she asked.
The 15 experts met under the NIH's state-of-the-science conference program, which aims to direct future research in an important study area.
They included specialists in geriatrics, long-term care, nursing, psychiatry and other fields. Panelists may not be federal government employees, nor may they have financial stakes in any treatments considered.
The Alzheimer's Association says as many as 5.3 million Americans have Alzheimer's and projects that 16 million may have it by 2050.
The panel found there were inconsistent definitions of what constitutes Alzheimer's disease and the cognitive decline that leads up to it.