People at high risk for dementia who took cholesterol-lowering statins are half as likely to develop dementia, according to a new study.

The study, which appears in Neurology, consisted of 1,674 older Mexican-Americans in Sacramento, California who were free of dementia at the start of the trial but who suffered from metabolic conditions that put them at risk for developing the condition. 27% of the participants took statins at some point in the study and over the five-year follow up period, 130 participants developed dementia or cognitive impairment.

Researchers adjusted for factors such as education, smoking status, the presence of a particular gene thought to predict dementia, and history of stroke or diabetes. Lead author of the study, Mary Haan, a professor of epidemiology at the University of Michigan’s School of Public Health, said “the bottom line is that if a person takes statins over a course of about 5-7 years, it reduces the risk of dementia by half, and that's a really big change".

Prof Haan said that "in older people you have so many different chronic conditions, especially in this group, that the chance of any intervention having an effect is fairly limited". She added: "Say you're 75 or 80 and you've got six diseases. How much is a treatment really going to help? This showed if you started using statins before the dementia developed you could prevent it in about half of the cases".

It is likely that many people taking statins have already benefited unknowingly from the dementia fighting properties, Prof Haan said, adding that she hopes the study will help fuel randomised trials to test statins and their ability to prevent dementia.

Prof Haan went on to say that "we aren't suggesting that people should take statins for purposes other than what they are indicated for, but hopefully this study and others will open the door to statin testing for dementia and other types of cognitive impairment".

It's not clear exactly how statins work to decrease the development of dementia, though an emerging risk factor is high insulin, she added. One theory is that statins may work on those insulin pathways in a way that lowers the high insulin levels in the brain that can lead to the classic Alzheimer's pathology.
The study was originally funded in 1997 to look at metabolic and vascular conditions like hypertension and diabetes and their effect on the risk of dementia and Alzheimer's disease. Earlier findings by Prof Haan's group established that people with type 2 diabetes are up to three times more likely to develop Alzheimer's.