An independent panel convened this week by the National Institutes of Health (NIH) concluded that the value of preventive strategies—such as mental stimulation, exercise, or dietary supplements—for delaying the onset or reduction in the severity of decline of Alzheimer's disease has not been demonstrated in rigorous studies.
"Alzheimer's disease is a feared and heart breaking disease," said Martha L. Daviglus, MD, conference panel chair and professor of preventive medicine and medicine at Northwestern University, Chicago. "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."
The panel said that its assessment this week of available evidence revealed that progress to understand how the onset of these conditions might be delayed—or prevented—is limited by inconsistent definitions of what actually constitutes Alzheimer's disease and cognitive decline.
Other factors were related to incomplete understanding of the natural history of the disease or limited understanding of the aging process in general. The panel recommended that the research community and clinicians collaborate to develop, test, and adopt objective measures of baseline cognitive function and changes over time.
Although various risk factors were examined, age was found to be the strongest known risk factor for Alzheimer's disease. Also, a genetic variant of a cholesterol ferrying protein—apolipoprotein E—had strong evidence in association with the risk for developing Alzheimer's disease.
In its review, the panel could determined no evidence that even any modifiable factors—such as use of dietary supplements, use of prescription or non prescription drugs, diet, exercise, or social engagement—was associated with a reduced risk of Alzheimer's disease.
However, they noted that although little evidence exists that these interventions lessen cognitive decline, some are not necessarily harmful and may confer other benefits.
"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?" Daviglus said.
The panel also found that certain chronic diseases—such as diabetes and depression—and risk factors such as smoking may be associated with increased risk of both Alzheimer's disease and cognitive decline. However, those studies have not yet showed that these medical or lifestyle factors actually cause or prevent Alzheimer's disease or cognitive decline.
To obtain stronger information, the panel called for more research—especially into areas that characterize the natural history and progression of these diseases in the community. They also recommended the establishment of registries for Alzheimer's disease and cognitive decline, modeled on existing registries for cancer.