Despite some reports that statins might slow or prevent Alzheimer's disease, a new study finds no evidence for the theory. 

While some animal studies have suggested this possibility, whether the same benefit translates to humans hasn't been clear, the researchers said.

"We didn't find a relation between statin use and the risk of Alzheimer's disease or a decline in thinking ability," said lead researcher Dr. Zoe Arvanitakis, an associate professor of neurology at Rush University Medical Center in Chicago.

In addition, brain autopsies found no effect of statins on the two main causes of dementia, Alzheimer's and stroke, Arvanitakis said.Statins (also known as HMG-CoA reductase inhibitors) form a class of hypolipidemic drugs used to lower cholesterol levels in people with or at risk of cardiovascular disease. They lower cholesterol by inhibiting the enzyme HMG-CoA reductase, which is the rate-limiting enzyme of the mevalonate pathway of cholesterol synthesis. Inhibition of this enzyme in the liver stimulates LDL receptors, resulting in an increased clearance of low-density lipoprotein (LDL) from the bloodstream and a decrease in blood cholesterol levels.

In the study, Arvanitakis' team collected data on 929 Catholic clergy who took part in the Religious Orders Study, which looks at aging and Alzheimer's disease. At the start of the study, all the participants were around 75 years old and had no signs of dementia. All had a brain autopsy after death, and each had yearly cognitive exams for up to 12 years.

The findings were published in the Jan. 16 online edition of Neurology.

When the study started, 119 people were taking statins. Over the 12 years of the study, 191 people developed Alzheimer's. Of these, only 16 had been taking statins.

Moreover, brain autopsies on more than 250 people who died during the study failed to find any evidence that taking statins had an effect on pathology of Alzheimer's disease or strokes, the scientists found.

"This study adds to the growing evidence that statins don't lower the risk of Alzheimer's disease," Arvanitakis said.

However, one expert thinks this study is not conclusive, and clinical trials that are under way should provide a definitive answer on the issue. "We will see the results of these trials fairly soon," said William Thies, vice president of medical and scientific affairs for the Alzheimer's Association.

"This finding fits in with a great deal of other work that has been done on statins," said Thies. "Most of these studies show a benefit, but this is not the first one to show there isn't a benefit."

Statins are excellent drugs for lowering cholesterol, Thies said. "But there is no recommendation that you take statins for Alzheimer's disease," he added.

Larry Sparks, director of the Roberts Laboratory for Neurodegenerative Disease Research at the Sun Health Research Institute in Arizona and one of the first to link statins with Alzheimer's prevention, doesn't think the study was large enough to give a definitive result.

In his own work, Sparks has found a benefit from statins in treating patients with mild to moderate Alzheimer's disease. However, he thinks the type of statin makes a difference.

"Research suggests that statins that don't get into the brain may prevent or slow the progression of Alzheimer's," Sparks said. "This is a continuing story."

SOURCES: Zoe Arvanitakis, M.D., associate professor, neurology, Rush University Medical Center, Chicago; William Thies, Ph.D., vice president, medical and scientific affairs, Alzheimer's Association, Chicago; Larry Sparks, Ph.D., director, Roberts Laboratory for Neurodegenerative Disease Research, Sun Health Research Institute, Sun City, Ariz.; Jan. 16, 2008, Neurology online