Cholesterol-lowering drugs known as statins may help reduce a person's risk of contracting Alzheimer's disease, according to a study published in the journal Jama Neurology on Monday (Dec 12).

An analysis of 400,000 Americans who took statins for at least two years found that high use of the drugs was associated with a lower risk for Alzheimer's disease.

But this benefit depends on the specific type of statin, and the gender and race or ethnicity of the person taking it.

For example, black men appeared to gain no benefit from taking any statin, while white women may lower their risk regardless of which statin they take, HealthDay News quoted the researchers.

The study found high exposure, defined as taking statins for at least six months in a given year during the study period, was associated with a 15 per cent decreased risk of Alzheimer's disease for women and a 12 per cent reduced risk for men, compared to those also prescribed statins but who took them more sporadically.

According to British newspaper The Telegraph, the link may be explained by an interplay between cholesterol, which is regulated by the drug, and beta-amyloid, which plays a role in dementia, or that an anti-inflammatory property of statins themselves could be protecting against the disease.

Professor Julie Zissimopoulos, who led the research, said: "The right statin type for the right person at the right time may provide a relatively inexpensive means to lessen the burden of Alzheimer's."

Dr Doug Brown, director of research and development at Alzheimer's Society, told The Telegraph: "Previous research has attempted to find out whether using statins to lower cholesterol can alter a person's risk of developing dementia but these studies have produced mixed findings.

"This new study goes some way towards clearing up this confusion by analysing large amounts of existing data of people who use different types of statins over a long period of time.

"Their refreshing approach highlights that 'one size fits all' is not always a suitable approach to healthcare and this is likely to be the case when it comes to ways people can reduce their risk of dementia."

HealthDay News quoted Dr Gail Li, an associate professor in the department of psychiatry and behavioral sciences at the University of Washington in Seattle who was not involved with the new study, as saying that statins do not seem to help patients who already have Alzheimer's.