Statin drugs, a commonly prescribed class of lipid-lowering drugs that include Lipitor, Zocor and Crestor, do not prevent Alzheimer's disease or dementia, according to a report in the Cochrane Database of Systematic Reviews.

"In late life there is good evidence that statins given to people at vascular risk have no effect in preventing Alzheimer's disease or dementia," Dr. Bernadette McGuinness from Queen's University Belfast, Belfast, UK told Reuters Health. "Statins cannot be recommended for this purpose therefore."

In an earlier review, two clinical reports had described an association between statin therapy and a reduction in the rates of Alzheimer disease by as much as 70 percent, McGuinness and colleagues explain, but there had been no randomized clinical trials performed at that point.

The investigators identified two published trials that included 26,340 participants. One compared simvastatin 40 milligrams with placebo, and the other compared pravastatin 40 milligrams with placebo.

There were no significant differences between any of the treatment groups in the percentage of participants classified as cognitively impaired, the researchers note.

Similarly, further analysis revealed "no significant association between any of the cognitive tests and statin therapy, the investigators say, "confirming the lack of effect of statin therapy on cognition."

"We were a little surprised at the lack of efficacy," McGuinness said, "biologically it seems feasible statins could be effective in preventing dementia due to their role in cholesterol reduction, coupled with the fact the initial observational studies were so promising. It does illustrate the importance of carrying out randomized controlled trials."

"We did demonstrate that statins were not detrimental to cognition, which had been a concern previously also," McGuinness added. "It is still unknown whether statins given for many years from mid-life on may have an effect."