Older people taking statin drugs are less likely to develop dementia than their counterparts who don’t take the pills, a study in the July 29 Neurology suggests.

While the provocative finding offers hope that the cholesterol-reducing drugs might help against Alzheimer’s disease and other forms of dementia, scientists say this study is unlikely to be the last word on the topic.

Indeed, it may just fuel an already lively debate over statins’ potential effect on dementia. Some research has hinted at benefits, while other studies, particularly in people with clear signs of Alzheimer’s disease, show no effect from the drugs.

In the new study, researchers tracked the health of 1,674 Mexican-Americans age 60 or older in the Sacramento, Calif., area starting in 1998.  Roughly one-fourth took statins during the five-year study, most for more than two years. During the study, 130 participants developed Alzheimer’s disease, other dementia or a pre-dementia condition such as memory loss that could be verified by tests.

Those taking statins were half as likely as those not getting the drugs to develop one of these impairments, says study coauthor Mary Haan, an epidemiologist at the University of Michigan in Ann Arbor.

The groups had similar smoking habits, blood pressure ranges, previous histories of stroke and the presence of a known gene variant linked to Alzheimer’s. The analysis accounted for slight differences between the groups in diabetes, education and age.

Most dementia arises from Alzheimer’s disease or from problems related to blood vessels, including strokes or mini-strokes.

The researchers excluded people who at the outset of the study had any signs of such cognitive impairment or who developed it within the first two years of the study — the latter to eliminate incipient problems that may have originated before the study began.

“This is a reasonable strategy,” says Robert Green, a neurologist and epidemiologist at Boston University. But grouping dementias also makes it difficult to know how the statins work, if they do. ”We could be looking at the impact of statin use on the vascular component rather than Alzheimer’s,” he says.

In any case, observational studies like this one carry less weight in the scientific community than trials in which researchers randomly assign people up front to get one treatment or another — quite often a placebo.

“While this is an intriguing study, the weight of evidence at the present time is still leaning away from statin efficacy” for Alzheimer’s or other dementia, Green says.

The issue is confounded because it remains unclear how drugs that reduce LDL-cholesterol might somehow limit brain damage. One hypothesis holds that the drugs might work by calming inflammation, but research into other anti-inflammatory drugs has failed to show clear benefits against Alzheimer’s.

Statins could have other effects. Gail Li, a psychiatrist at the University of Washington in Seattle, and her colleagues used autopsy data to report last year that the brains of people who had taken statins showed less evidence of tangled tau proteins inside brain cells than those of people who didn’t take statins. The presence of these tangles is a sign of Alzheimer’s disease.

Li says that Alzheimer’s disease may have a 10-year or even 20-year head start before showing symptoms. Giving statins to someone with obvious disease might be too late, she says. Prescribing drugs earlier, or even for young people, could be more effective at fighting the disease. “We might see an age effect,” Li says.

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