A US study that followed over 1,500 older Mexican Americans for 5 years found that statin users
were about half as likely to develop dementia, or to have cognitive impairment without dementia, as
those who did not use statins. Statins are normally prescribed for lowering LDL or "bad" cholesterol.
The study is published in the 29th July online issue of Neurology and was the work of researchers at the University of Michigan, Ann Arbor, led by Mary Haan, epidemiology professor at the University's School of Public Health.
Previous research has shown mixed results about the effect of cholesterol lowering drugs on cognitive function. For this longitudinal study, the researchers tested the link between statins and incidence of dementia and cognitive impairment without dementia over 5 years of follow up.
The participants were 1,789 older Mexican Americans in Sacramento, California, who suffered from metabolic conditions such as high cholesterol, type 2 diabetes and high blood pressure, that put them at higher risk of developing dementia, Alzheimer's Disease, or cognitive impairment without dementia.
The participants underwent cognitive and clinical evaluations every 12 to 15 months such that those who fell below a specific threshold on the cognitive tests had clinical tests. Diagnoses of dementia were independently confirmed by an adjudication team.
The results showed that:
- 452 (27 per cent) of the 1,674 participants free of dementia at the start of the study took statins at some point during the study.
- Over 5 years of follow up, 130 participants (8 per cent) developed dementia or cognitive impairment without dementia.
- After adjusting for education, smoking status, inherited factors, and history of stroke or diabetes at the start of the study, participants who used statins were about half as likely as those who did not use them to develop dementia or cognitive impairment without dementia. (Cox proportional hazard ratio = 0.52; 95 per cent confidence interval = 0.34 to 0.80).
"Statin users were less likely to have incident dementia/cognitive impairment without dementia during a 5-year follow-up."
They suggested that their findings added to the emerging evidence of a "protective effect of statin use on cognitive outcomes".
In a separate statement, Haan said that:
"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."
She also emphasized that the study looked at statins as a preventative, not a treatment for existing dementia.
In earlier research on this cohort, which was originally recruited in 1997 to investigate the risk on dementia and Alzheimer's of metabolic and vascular conditions like high blood pressure and diabetes, Haan and colleagues found people with certain metabolic conditions were at higher risk of Alzheimer's and dementia. For example, they found that people with type 2 diabetes were nearly three times more likely to develop Alzheimer's.
Haan explained the potential impact of using statins earlier rather than later, in a high risk group:
"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."
"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," she added.
The researchers suggest that many people on statins don't realize that they are possibly protecting themselves from dementia, and hope their findings will prompt others to set up randomized trials to test the effectiveness of statins at preventing dementia.
Haan said people should not use these findings as a reason to start taking statins for anything other than what they are indicated for, but she hoped that these findings will:
"Open the door to statin testing for dementia and other types of cognitive impairment."
Haan said it was not clear how statins worked to protect against dementia and cognitive impairment, but one emerging risk factor is high insulin, and perhaps statins lower insulin levels in the brain, since high levels of brain insulin have been linked to Alzheimer's symptoms. Further research is planned to find out exactly what happens at the biochemical level.
"Use of statins and incidence of dementia and cognitive impairment without dementia in a cohort study."
Cramer, C., Haan, M. N., Galea, S., Langa, K. M., Kalbfleisch, J. D.
Neurology 2008; 71: 344-350
Published online, July 29 2008, Volume 71, Issue 5
Click here for Abstract.
Source: University of Michigan, journal abstract.
Written by: Catharine Paddock, PhD