Although an increasing number of studies show that elevated serum cholesterol levels might be part of the cause of Alzheimer, a review of studies concludes that statin medications (SMs) will not help prevent Alzheimer’s.
SMs lower cholesterol by inhibiting a key enzyme used by the body to make it, which decreases cholesterol formation and helps reduce the amount of LDL cholesterol.
The image depicts a normal brain on top and an Alzheimer’s brain below.
Biomedical and epidemiological studies showing the relationship between elevated cholesterol and Alzheimer’s have caused scientists to wonder if these medications could lower the risk of developing Alzheimer’s, which is the most common cause of dementia. For example, in studies using animals, the expression of Alzheimer’s symptoms slowed with lowered cholesterol, giving hope that the same might be true for humans.
“From these trials, which contained very large numbers and were the gold standard, it appears that SMs given in late life to individuals at risk of vascular disease do not prevent against dementia and Alzheimer’s,” said lead study author Bernadette McGuinness. “I feel the follow-up time was sufficient to allow for an effect to appear,” she added.
The review, an update to an earlier review completed in 2001, comprised 26,340 participants in two major studies. One study, the Medical Research Council/British Heart Foundation Heart Protection Study (HPS), looked at simvastatin (Zocor) use in 20,536 patients and followed them for five years. The other study, the PROSPER trial, looked at pravastatin use in 5,804 patients, with an average follow-up of 3.2 years.
Both studies were double-blind randomized, placebo-controlled studies of SMs in individuals at risk for dementia and Alzheimer’s. Taken together, the studies comprised adults between the ages of 40 and 82.
While the review showed no evidence that SMs were harmful to cognition, the review authors found no difference between patients receiving the medications and patients receiving placebo medications when it came to incidence of dementia, cognitive function or performance on specific neuropsychological tests, such as a picture word learning test.
“SMs have a range of mechanisms that could help or hurt cognition,” said Beatrice Golomb of the department of family and preventive medicine at the University of California, San Diego. “Regarding SMs as preventive medicines, there are a number of individual cases in case reports and case series where cognition is clearly and reproducibly adversely affected by SMs.”
Golomb also said that some randomized trials have shown that the net effect of SMs was significantly adverse and others that have shown it was neutral, but that none has shown statin use to be favorable for cognition.
McGuinness said that while the two large trials showed that SMs given later in life do not protect against dementia or Alzheimer’s, “it is unclear, however, if SMs given in middle age for many years can protect against dementia in later life, as the studies did not address this.”
She noted that neither study aimed to assess the prevention of dementia primarily; in fact, dementia was at most a secondary outcome in the studies. As a result, “some people with dementia may not have been picked up by the screening, especially in HPS, but it is difficult to know.”
Patients taking SMs might not take them reliably if they’ve developed cognitive problems or side effects, Golomb said. “That is, the very patients who develop cognitive problems or adverse effects as a result of SMs will be less compliant on SMs, the literature says, and then may be selectively excluded from the study.” As a result, the study could portray unrepresentatively favorable results where cognitive function is concerned, she said. “However, the conclusion, an important one, remains largely correct.”
References:
1. McGuinness B, et al. Statins for the prevention of dementia. Cochrane Database of Systematic Reviews 2009, Issue 2.
