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No evidence of even moderate scientific quality links the risk for Alzheimer's disease to any modifiable factor such as diet, drugs, demographics, co-morbidity or environmental exposure, according to a consensus statement.
While promising research is under way on numerous factors, published evidence is weak or inconclusive, according to a consensus statement written by a panel of the National Institutes of Health and published early online by Annals of Internal Medicine.
The panel considered evidence from 127 observational studies, 22 randomized, controlled trials and 16 systematic reviews to draw conclusions and make recommendations for further research.
While some lifestyle factors such as a Mediterranean-style diet, omega-3 fatty acids and physical and leisure activities were associated with a lower risk of cognitive decline, available evidence is too weak to justify strongly recommending them to patients.
No consistent associations were found for other vitamins; fatty acids; metabolic syndrome; blood pressure; plasma homocysteine level; obesity and body mass index; antihypertensive medications; nonsteroidal anti-inflammatory drugs; gonadal steroids; or exposures to solvents, electromagnetic fields, lead or aluminum.
Likewise, some factors, such as the gene marker apolipoprotein E, depression and metabolic syndromes, were associated with a higher risk of cognitive decline, yet evidence was also limited. Stronger evidence showed that people who smoke or have diabetes are at an increased risk for cognitive decline.
While the researchers could not draw firm conclusions about modifiable risk factors, they added that a large amount of promising research on medication, diet, exercise, and cognitive engagement is under way. The panel recommended that future research:
- use rigorous, consensus-based diagnostic criteria; further develop brain imaging techniques to pinpoint pathological changes; and delineate the natural progression of Alzheimer's disease;develop an objective, consensus-based definition of mild cognitive impairment to further aid research;collect data from caregivers in a systematic way;involve large-scale, long-term population-based studies using precise, well-validated exposure and outcome measures to generate strong evidence on biological, behavioral, lifestyle, dietary, socioeconomic, and clinical factors;include women and men from socioeconomically and ethnically diverse populations to examine the incidence and prevalence of Alzheimer's disease and cognitive decline in these groups and specific subgroups; andcreate a large, multicenter registry, following the models of cancer, that would greatly expand opportunities for research and surveillance.