There is no strong evidence that any dietary or lifestyle changes can reduce a person's risk of developing Alzheimer's disease, a US government panel said on Monday.
Experts called together by the National Institutes of Health examined scores of studies about whether diet, exercise, nutritional supplements and chronic diseases like diabetes or hypertension affect a person's risk of getting the fatal, brain-wasting disease.
They found some signs that diabetes, high cholesterol and smoking could raise the risk of Alzheimer's.
And they found that eating a Mediterranean-type diet -- high in healthy fats, fruits and vegetables -- and taking folic acid, cutting back on alcohol and keeping the brain and body fit appear to lower the risk.
But in every case, the evidence was not strong enough to say for sure, the panel found.
"Although numerous studies have investigated risk factors and potential therapies for Alzheimer's disease, significant gaps in scientific knowledge exist," Dr Martha Daviglus of Northwestern University Feinberg School of Medicine, Chicago, and colleagues wrote in the Archives of Neurology.
"Currently, firm conclusions simply cannot be drawn about the association of any modifiable risk factor with Alzheimer's disease, and there is insufficient evidence to support the use of any lifestyle interventions or dietary supplements to prevent Alzheimer's," the panel wrote.
Old age remains the most reliable known risk factor for the disease, which afflicts 26 million people worldwide.
People with a specific variant of the apolipoprotein E or APOE gene are also at greater risk.
The US panel called for large-scale, long-term, population-based studies and clinical trials to evaluate what, if anything, can be done to slow or stop its progression.
In the meantime, the experts said older people and those with Alzheimer's in their family should keep active and do all they can to maintain good health.
"Until more conclusive results are available, individuals should continue to aim for a physically and mentally active and healthy lifestyle and prevention of the well-known major risk factors for chronic diseases," they wrote.
The Alzheimer's Association said significant increases in federal funding for disease research were needed to conduct the studies called for in the NIH panel's report.
"It is clear that there is a relationship between heart health and brain health, and this relationship needs further research so that we can make definitive recommendations," the group said in a statement.
"Nonetheless, even now with the preliminary evidence that we have, this connection is another good reason to live a healthy lifestyle that is beneficial for your heart health such as controlling your cardiovascular risk factors -- your blood pressure, blood sugar, and body weight."
Policy-makers and drug companies are working furiously to find ways to prevent Alzheimer's as the Baby Boom generation heads into old age.
Of the 5.4 million Americans with the disease, an estimated 4% are under 65, 6% are 65 to 74, 45% are 75 to 84, and 45% are 85 or older.
