Benefits of hormone replacement therapy in protecting women from Alzheimer's inconclusive

A rigorous evaluation of the scientific literature reveals that the jury is still out when it comes to hormone replacement therapy and a woman's risk for Alzheimer's disease. Alzforum (http://www.alzforum.org) asked prominent scientists to analyze the results of published studies examining the effects of estrogen or estrogen-plus-progesterone therapy on women. Their analysis, reported in the AlzRisk database (http://www.alzrisk.org), discloses that while some studies hint at a possible benefit in protecting women from Alzheimer's, more research is needed before reaching a definitive conclusion. Alzforum writer Madolyn Bowman Rogers summarizes the findings in a story published this week in Alzforum (http://www.alzforum.org/new/detail.asp?id=2954), while leading experts weigh in on the topic.

AlzRisk database curators Jennifer Weuve at Rush University, Chicago, Illinois; Deborah Blacker at Massachusetts General Hospital, Boston; and Jacqueline O'Brien at the Harvard School of Public Health reviewed results from all available observational studies conducted to date that qualified for inclusion in AlzRisk.

Observational studies are less rigorous than randomized trials, which are the gold standard for drawing conclusions about the risks and benefits of medicines. In observational studies, scientists have no control over who is taking the medication and who is not, whereas in randomized controlled trials, each participant is randomly assigned to either a treatment group or a control group before the start of the study, ensuring that equal numbers of people with similar attributes are compared. The AlzRisk database curators excluded from their analysis findings from randomized controlled trials, some of which show, in fact, that estrogen increases the risk for dementia, because none of those studies focused on Alzheimer's disease, looking instead at dementia for all causes more generally. AlzRisk meta-analyzes data for Alzheimer's risk factors specifically.

The AlzRisk database is a rich source of information for scientists, reporters, and the public. It catalogues, compares, and meta-analyzes all epidemiological reports on environmental (i.e., non-genetic) risk factors for Alzheimer's. In essence, it offers a final word on what the available body of literature on a particular risk factor amounts to at the present time. Hormone replacement therapy is the latest addition; other factors reviewed so far include blood pressure, diabetes, homocysteine, antioxidants, physical activity, and inflammation. Sometimes the findings of AlzRisk confirm prevailing opinions about the given risk factor at the time; other times they do not. But in every case, the AlzRisk findings arise from a strict apples-to-apples comparison of the existing literature.