A comprehensive analysis by an independent government panel has found that there is not enough scientific evidence to date to support the advice doctors currently give such as exercising, doing crossword puzzles or eating a Mediterranean-style diet for preventing or controlling symptoms of Alzheimer's disease and dementia.
As rates of age-related dementia and Alzheimer's disease have continued to rise in the U.S. largely because Americans are living longer and the over-65 population has swelled to record highs researchers have worked relentlessly to understand the causes of these mind-robbing diseases and to help prevent or slow their progression. To clarify the state of the current evidence and offer physicians clearer treatment guidelines, the National Institutes of Health (NIH) in early 2009 commissioned a detailed analysis of existing studies, covering 165 papers published between 1984 and 2009.
The resulting analysis of the findings, along with the NIH consensus statement based on the results, published Monday, are somewhat surprisingly and disappointingly contrary to what has become common medical practice for Alzheimer's prevention.
For years, the prevailing hypothesis has been "Use it or lose it" when it comes to avoiding gradual age-related mental decline. Data has associated behaviors such as keeping the mind actively engaged throughout life, staying physically active, eating certain foods and supplementing the diet with specific vitamins and nutrients with lower rates of dementia in old age. These lifestyle factors appeared to limit cognitive decline of various kinds, from occasional "senior moments" to the more serious episodes of cognitive impairment that can be a prelude to Alzheimer's disease.
Now researchers at Duke University report in the current issue of the Annals of Internal Medicine that the data on the preventive effects of lifestyle factors is not as strong as they had thought. Led by Brenda Plassman, a professor of psychiatry and behavioral sciences, the study authors analyzed decades' worth of research, including observational studies in which scientists looked retrospectively at a group of participants to tease out associations between certain behaviors (like exercise) and selected effects (like scores on tests of memory and cognitive skills), as well as the more definitive clinical trials that randomly assign volunteers to intervention or control groups and then assess how the intervention affects cognitive ability.
Overall, the researchers say they were dismayed with the paucity and weakness of the existing evidence. "When we applied rigorous but consistent standards to review all the studies, we found that there was not sufficient evidence to recommend any single activity or factor that was protective of cognitive decline later in life," says Plassman.
However weakly, though, the review did support what doctors know about risk factors for cognitive decline: smoking, diabetes, depression, metabolic syndrome (the constellation of conditions including high blood pressure, obesity and high cholesterol that are associated with heart disease and diabetes) and specific gene variants were all linked with increased risk of developing Alzheimer's disease. In addition, preventive behaviors such as eating a Mediterranean diet (high in fruits and vegetables, omega-3 fatty acids and unsaturated fats), exercising, maintaining cognitive engagement (doing puzzles, learning new things) and fostering extensive social relationships were linked to a lower risk.
The problem is that none of these relationships were particularly robust, the authors say. And none were strong enough to justify recommending the behaviors to people who want to prevent or slow down the onset of dementia.
The findings led the NIH to issue Monday's state-of-the-science statement, in which the agency notes, "Currently, firm conclusions cannot be drawn about the association of any modifiable risk factor with cognitive decline or Alzheimer's disease." Although the statement does not constitute an official policy or government recommendation, it serves as a guideline for doctors advising patients about the best evidence on the role of lifestyle factors in Alzheimer's prevention.
And that evidence, experts say, still suggests there are good reasons for continuing current practices, even if they cannot necessarily be expected to hold off dementia. These behaviors are known to benefit health in many other ways, namely lowering the risk of obesity, diabetes and heart disease and improving mood. And longer-term studies currently under way may eventually provide stronger scientific evidence to show they help prevent dementia and Alzheimer's disease as well. "There are probably physicians who will recommend these activities to promote cognitive health," says Plassman. "Our review suggests that there is currently not a lot of strong evidence to show that they are helpful. But the flip side is that there is little to no risk or harm in doing them either."
The Alzheimer's Association, for its part, will continue advising its members and interested patients to eat a healthy diet and engage in socially and physically rewarding activities. "There are hints in the data that offer hope that by changing lifestyle factors and other things, we can in fact perhaps reduce the risk of dementia in the future," says Dr. Maria Carrillo, senior director of medical and scientific relations at the Alzheimer's Association. "We feel that we are on the right track."
What's needed now, as Plassman's group notes, is more long-term research that documents such benefit. "We need that type of investment in Alzheimer's disease research for the future," says Carrillo.