A 2016 Cochrane systematic review identified 2 double-blind RCTs that evaluated statins for preventing cognitive decline and dementia in patients with either risk factors or a history of vascular disease.1 The authors couldn’t perform a meta-analysis because of heterogeneity.
Statins don’t prevent dementia
The first RCT found that 5804 patients (70-82 years old with pre-existing vascular disease or increased risk because of smoking, hypertension, or diabetes) manifested equivalent cognitive decline at 3.5 years after random assignment to pravastatin 40 mg/d or placebo.2 Investigators measured cognition with the Mini-Mental State Exam (MMSE), which scores cognitive function on a scale of 0 to 30, with higher numbers indicating better function (mean difference [MD] at follow-up=0.06 points; 95% confidence interval [CI], −0.04 to 0.16).
A second RCT evaluated simvastatin 40 mg/d or placebo for as long as 5 years in 20,536 patients 40 to 80 years of age with a history of coronary artery disease or diabetes.3 The study excluded patients with dementia at baseline. The odds of developing dementia didn’t differ between groups (odds ratio=1.0; 95% CI, 0.61-1.65).
Both studies were originally designed to measure cardiovascular outcomes. The authors rated both as high quality with a low risk of bias.
A contrast to earlier, lower-quality studies
These results contrast with an earlier meta-analysis based on one of the previously described RCTs and lower-quality evidence (16 cohort studies and 3 case-control studies) that found using statins to be associated with lower relative risk (RR) of dementia than not using a statin (all-type dementia RR=0.82; 95% CI, 0.69-0.97; Alzheimer’s disease RR=0.70; 95% CI, 0.60-0.83).3,4
The total patient population was more than 2 million and varied widely. Duration of statin use and type of statin (simvastatin, atorvastatin, fluvastatin, pravastatin, rosuvastatin) also varied. The authors noted potential bias in results for 2 reasons: Cross-sectional studies included patients with impaired cognition who were less likely to be prescribed statins, and statin use was determined by patient self-report.
Statins don’t treat dementia
A Cochrane review that included 4 RCTs with 1154 patients, 50 to 90 years old, assessed the effect of ≥6 months of statin therapy (atorvastatin 80 mg/d or simvastatin 40-80 mg/d) on the course of Alzheimer’s disease and vascular dementia.5 Most patients had mild to moderate dementia and most were also taking an anticholinesterase inhibitor.
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