Evidence insufficient on relationship of modifiable factors with risk of Alzheimer's disease

The available evidence is insufficient to draw firm conclusions about the association of modifiable factors and risk of Alzheimer's disease (AD), according to a report posted online today that will appear in the September issue of Archives of Neurology.

Estimates suggest that up to 5.3 million people in this country may have AD, and this number will likely increase as baby boomers grow older. In fact, "age is currently the strongest known risk factor for AD," write the authors. Variation in the apolipoprotein E (APOE) gene is also associated with the risk of developing AD. However, existing research to ascertain other risk factors for the condition has been less conclusive.

From April 26 to 28, 2010, the National Institutes of Health convened a State-of-the-Science Conference to examine studies of potential AD risk factors and possible preventive measures. The conference evaluated existing English-language research found in MEDLINE and the Cochrane Database of Systematic Reviews from 1984 through October 27, 2009, as well as a formal evidence report. Topics considered were nutritional supplements and dietary factors, physical activity, other chronic conditions (diabetes, high cholesterol, high blood pressure), substance use (cigarettes, alcohol), and cognitive engagement. Panelists weighed the level of evidence for each risk factor (low, moderate or high) and rated studies accordingly (low for observational studies vs. high for randomized controlled trials).

Martha L. Daviglus, M.D., Ph.D., from Northwestern University Feinberg School of Medicine, Chicago, and colleagues summarized the panel's findings. The group determined "that currently there is no evidence of even moderate scientific quality supporting the association of any modifiable factor with reduced risk of cognitive decline or AD." While some studies appeared to show an increase or reduction of AD risk or progression, they were not strong enough to draw firm conclusions. The authors call for large-scale, long-term, population-based studies and clinical trials to answer these questions. "It is hoped that the panel's report will instigate rigorous high-quality research that can provide conclusive evidence on this issue," they write. "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."