Strong modifiable risk factors for AD elusive
MedWire News: Associations between lifestyle factors and the risk for Alzheimer's disease (AD) are based on low-level evidence and are not robust, says an expert panel.
"Although numerous studies have investigated risk factors and potential therapies for AD, significant gaps in scientific knowledge exist," say Martha Daviglus (Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA) and colleagues.
"Currently, firm conclusions simply cannot be drawn about the association of any modifiable risk factor with AD, and there is insufficient evidence to support the use of any lifestyle interventions or dietary supplements to prevent AD."
The independent panel first reported its conclusions at a State-of-the-Science Conference convened by the National Institutes of Health. It has now produced an article, published in the Archives of Neurology, to detail its findings and address the "many concerns" generated by the original report.
The panel assessed cohort studies with at least 300 participants and randomized, controlled trials with at least 50 patients published from 1984 through October 2009. It found that, overall, diabetes mellitus, hyperlipidemia in midlife, and current smoking were associated with an increased risk for AD, whereas a Mediterranean-style diet, sufficient folic acid intake, low or moderate alcohol intake, and pursing cognitive activities and physical activity were all linked to a reduced risk for AD.
However, the level of evidence, according to the Grading of Recommendations Assessment, Development, and Evaluation criteria was low.
Although many of the individual studies assessed were of good quality, almost all were observational, cohort studies, or systematic reviews or meta-analysis of such studies. Research into risk factors such as physical activity and diet generally relied on self-reported measures, which were rarely objectively verified. Many studies did not adjust their findings for potential confounders.
There was much heterogeneity among the studies, so meta-analysis was often impossible. Even for discrete, verifiable risk factors such as diabetes, diagnostic criteria varied among studies, and factors such as duration of diabetes and degree of glycemic control were often not accounted for.
Studies were also compromised by limited knowledge of the natural course of AD, and variable use of consensus-based diagnostic AD criteria.
"It cannot be emphasized enough that while risk factors and preventive measures studied so far have at best been only loosely associated with AD, carefully designed future studies may yet establish significant associations between these same factors with prevention of AD," say Daviglus et al.
"It is hoped that the panel's report will instigate rigorous high-quality research that can provide conclusive evidence on this issue."
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By Eleanor McDermid