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a Palmetto Health Alliance/University of South Carolina, Columbia
Ihab Hajjar, Clinical Assistant Professor, Department of Internal Medicine, Division of Geriatrics, Palmetto Health Alliance/University of South Carolina, 9 Medical Park, Suite 230, Columbia, SC 29203 E-mail: ihab.hajjar{at}palmettohealth.org.
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Abstract |
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Methods. This is a case-control and a retrospective cohort study of a community-based ambulatory primary care geriatric practice. We included a convenience sample of all patients (N = 655, mean age 78.7 ± 0.3 years, 85% Caucasian, 74% women) with hypercholesterolemia or dementia, or using statins. We compared those using statins with those who do not with respect to the clinical diagnosis of dementia and its subtypes and the progression of cognitive impairment.
Results. At the initial visit, 35% had dementia, and 17% were using statins. After covariate adjustments, patients on statins were less likely to have dementia (odds ratio [OR] for dementia based on composite definition = 0.23; 95% confidence interval [CI] [0.1–0.56], p = .001, OR Alzheimer's disease = 0.37; 95% CI [0.19–0.74], p = .005, OR vascular dementia = 0.25; 95% CI [0.08–0.85], p = .027). At follow-up, patients on statins showed an improvement on their Mini-Mental Status Examination score by 0.7 ± 0.4 compared to a decline by 0.5 ± 0.3 in controls, p = .025 (OR for no change or improvement on statins = 2.81; 95% CI [1.02–8.43], p = .045) and scored higher on the Clock Drawing Test (difference of 1.5 ± 0.1, p = .036).
Conclusions. The use of statins is associated with a lower prevalence of dementia and has a positive impact on the progression of cognitive impairment.
MANY studies, both cross-sectional and longitudinal, have found an association between metabolic cardiovascular syndromes and dementia (1)(2)(3)(4)(5)(6). Hyperlipidemia in particular has been identified as a possible risk factor for both vascular dementia and Alzheimer's disease (AD) (5)(7)(8)(9)(10)(11)(12)(13). This risk relationship is supported by animal models and cross-national surveys. For example, mice fed a high-cholesterol diet have a twofold increase in the ß-amyloid protein and an increase in the number and size of amyloid deposits (14). Countries that have high dietary fat consumption tend also to have a higher prevalence of AD (6).
It is theoretically possible then that treatment of hyperlipidemia could lessen the risk of dementia and slow the progression of the disease. In fact, prior preliminary data have shown that individuals treated with 3-hydroxy-3-methylglutaryl-coenzyme-A reductase inhibitors (statins) have a lower prevalence of dementias of both vascular and Alzheimer's types (14)(15). However, data are very sparse concerning the impact of statins on the progression of cognitive impairment in individuals with hyperlipidemia or dementia.
We conducted a retrospective study on the association between statin use and the prevalence of dementia and the progression of cognitive impairment using chart review of elements of a standardized geriatric assessment and medication records of patients of a primary care geriatric practice.
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Methods |
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Patients selected for this study were all those with the diagnosis of hypercholesterolemia or dementia (AD, vascular dementia, mixed-type dementia, or Diffuse Lewy Body disease) or patients using statins. Because the practice was relatively new, all patients enrolled between 1997 and 2001. Data recorded at the initial visit included age, gender, race, smoking history, alcohol consumption, level of education, family history of dementia or AD, clinical diagnosis of hypertension, stroke, transient ischemic attack (TIA), and depression. All patients diagnosed with hypercholesterolemia and dementia were noted. When available, date of onset and type of dementia (AD, vascular dementia, mixed-type dementia, or Diffuse Lewy Body disease) were recorded. Cognitive and mood assessments were performed at baseline and follow-up. The Folstein Mini-Mental Status Examination (MMSE) (16), Clock Drawing Test (CDT) (17), and the Geriatric Depression Scale (GDS) (18)(19) were administered by a trained geriatric social worker to all patients, using a uniform procedure. Two social workers performed all the testing, minimizing interoperator variability. We use the scale of 7 (with 7/7 as the perfect score) for CDT scoring.
Statin use at baseline and duration of use were also recorded. To confirm use of statins, prescriptions written and provided to patients during the period of follow-up were recovered from the charts. In addition, we extracted data on baseline and continuing use of aspirin, donepezil (Aricept), vitamin B12, and vitamin E.
Physical exam information included blood pressure readings and heart rate. We used the higher of the left or right arm while sitting. Laboratory information included total cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and triglyceride (TG). We used only values obtained in our local laboratory to minimize variations. For follow-up examinations, we extracted information on blood pressure, heart rate, cholesterol level, LDL, HDL, and TG from charts as well as medications used, MMSE, CDT, and GDS.
To operationalize the diagnosis of dementia for this study, we developed a composite variable with a positive diagnosis when both a clinical diagnosis of dementia or one of its types were documented in the chart and the patient had a MMSE score less than 24. This cutoff has been shown to improve diagnostic accuracy (20). We performed the analysis using this composite variable, as well as each individual diagnostic criterion (clinical diagnosis and MMSE score). For the longitudinal analysis of cognitive change, we used the absolute change in MMSE score and CDT score between the follow-up cognitive testing and baseline testing at the initial visit.
Practice enrollment data were used for the analysis of dementia/cognitive impairment prevalence. The study of cognitive status change was conducted on patients for whom follow-up cognitive testing data were available. Patients were assigned to the "statin" group (those using statins at the initial visit) or the control group (not using statins). Review of the control charts indicated that none of the patients in this group had been exposed to statins. A chi-square test compared prevalence of dementia in the two groups. Bivariate and multivariate analyses were employed to explore the impact of other potential dementia risk factors. Multiple logistic, linear regression, and stepwise regression techniques were used to develop models, adjusting for multiple covariates. Goodness-of-fit tests were used to select the best-fitted models (21). Covariates included age, gender, race, education, smoking, alcohol, blood pressure, medical diagnoses (stroke or TIA, hypertension, depression), family history of dementia or AD, cholesterol level, LDL, HDL, and TG. Models were tested for the composite variable, clinical diagnosis of dementia, AD, vascular dementia, mixed dementias, MMSE, and CDT. The institutional review board approved the study at the local institution.
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Results |
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All models developed to adjust for covariates showed a persistent association. After adjusting for age, gender, race, education, blood pressure, family history of dementia, cholesterol, LDL and triglyceride levels, clinical diagnosis of stroke, TIA, depression, and hypertension, GDS, use of alcohol and smoking, and medications used, current use of statin was associated with a lower risk of dementia based on all criteria and for both AD and vascular dementia (odds ratio [OR] for dementia based on composite definition = 0.23; 95% confidence interval [CI] [0.1–0.56], p = .001; OR for dementia based on chart diagnosis = 0.16; 95% CI [0.09–0.27], p < .001; OR based on MMSE cutpoint = 0.23; 95% CI [0.1–0.55], p = .001; OR for AD = 0.37; 95% CI [0.19–0.74], p = .005; OR for vascular dementia = 0.25; 95% CI [0.08–0.85], p = .027) (Fig. 1).
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When compared with the cognitive testing at the initial visit, the statin group showed an improvement in their MMSE scores by 0.7 ± 0.4 versus a decline of 0.5 ± 0.3 points in the control group at follow-up (p = .025) (Fig. 2). After covariate adjustments including other medication use, patients on statins were more likely to show improvement or no change as compared to the control group (OR of having an improvement or no change on their MMSE = 2.81; 95% CI [1.02–8.43], p = .045). In addition, at follow-up, the statin group persistently had higher CDT scores as compared with the control group (p = .036) (Table 3 ).
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Discussion |
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There is increasing evidence to suggest an important role of cholesterol in the pathophysiology of dementia and AD (7)(8)(11)(12)(23)(24)(25). For example, Jarvik and colleagues found an increased risk of AD in patients with hypercholesterolemia (8). In the Rotterdam study, hyperlipidemia was found to be associated with vascular dementia and AD (3). Statins lower cholesterol levels by inhibiting cholesterol synthesis, decreasing LDL circulation, and modulating the LDL receptor (26). In addition, statins have an effect on nitric oxide, decrease endothelin, and may have an antioxidant effect (27)(28)(29)(30). The mechanism of the potential effect of statins on dementia and cognitive impairment is unknown. Our study showed an association between the use of statins and dementia, both vascular dementia and AD. This association was persistent even after adjusting for cholesterol, LDL levels, and stroke, suggesting that the effect of statins is independent of their effect on cholesterol and stroke prevention.
One limitation of this study is "bias by indication" (31)(32), which implies that statins are less likely to be prescribed to patients with dementia. Although we understand that this is a major problem of any cross-sectional or retrospective analysis that investigates the impact of an intervention, both the control and the statin groups were similar in many risk factors for dementia. Both groups were similar in education, alcohol consumption, tobacco use, stroke or TIA, and depression. We also performed multivariate analyses controlling for many covariates that could potentially affect the physicians' prescribing of the statin drugs. The impact of statins on dementia prevalence remained after these adjustments, minimizing the impact of this bias. Also, the association was persistent in the longitudinal analysis at follow-up, suggesting that the effect of statins is more likely to be valid and not only due to the bias by indication.
Another limitation of this study is the accuracy of the diagnosis of dementia. We were not able to confirm the diagnosis of dementia or its subtypes in the patients selected. The diagnosis of dementia is mostly a clinical diagnosis that is relatively accurate (33). We used two cognitive measures and developed a composite variable based on the clinical diagnosis and cognitive testing, which should improve diagnostic accuracy. The high rate of concordance between the clinical diagnosis and the cognitive testing results suggests accuracy of the diagnosis of dementia. In our sample, the majority of patients with a clinical diagnosis of dementia had no documented subtype. The impact of statins was true for these patients as well as for the overall sample and for those with either vascular dementia or AD, making the impact of this limitation on our results relatively low.
In part due to the recent growth in patient enrollment, many patients did not have follow-up cognitive testing. This limited our ability to perform subgroup analysis. There were no differences, including in cognitive testing score at baseline or use of statins, between the patients who had documented cognitive testing on follow-up and those who did not. Therefore, missing data from our analysis most likely have little impact on our results.
We had little information on patients' compliance with the use of statins. The finding that the mean cholesterol and LDL of the statin group was lower than the control group suggests that the patients were using the prescribed drugs. Our study was not designed to test the impact of other lipid-lowering agents or to compare the differences between the multiple statin drugs. We did not assess the incidence of adverse drug reaction from statins or the rate of drug withdrawal. A similar percentage of patients was using statins at baseline and at follow-up. We also could not assess the impact of statins on cognition beyond the follow-up period.
Until a randomized trial is performed, evidence concerning the impact of statins on dementia and their potential benefit for cognitive function will depend largely on observational studies. Our study suggests that the use of statins is associated with a lower prevalence of vascular dementia and AD. In addition, we have found a potential benefit of the use of statins on the progression of cognitive impairment in a select group of older patients followed in a community-based primary care geriatric practice. Clinical trials are urgently needed to confirm the positive impact of these drugs on cognitive function and dementia.
Received February 13, 2002
Accepted February 15, 2002
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