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Total serum cholesterol and ischemic heart disease risk in clinical trials and observational studies
1Department of Epidemiology, School of Public Health, University of North Carolina, Chapel Hill 27514.
Insights
Aggregated clinical trial data confirm the lipid hypothesis, showing that lowering total cholesterol significantly reduces ischemic heart disease (IHD) risk. This supports cholesterol reduction as a strategy for preventing IHD in middle-aged men.
Area of Science:
- Cardiovascular Medicine
- Epidemiology
- Clinical Trials
Background:
- Elevated plasma cholesterol is causally linked to ischemic heart disease (IHD).
- Individual clinical trials on the lipid hypothesis have yielded inconclusive results.
- Aggregate analysis of trials offers a more robust assessment of cholesterol's role in IHD.
Purpose of the Study:
- To aggregate and analyze clinical trial data to confirm the lipid hypothesis.
- To evaluate the dose-response relationship between cholesterol reduction and IHD risk.
- To validate findings using data from the Lipid Research Clinics Coronary Primary Prevention Trial (LRC-CPPT).
Main Methods:
- Meta-analysis of individual clinical trials on cholesterol-lowering interventions.
- Comparison of cholesterol reduction efficacy with IHD risk reduction.
- Validation against community-based epidemiological data (e.g., Framingham Study).
Main Results:
- A significant dose-response relationship exists between cholesterol lowering and IHD risk reduction.
- The LRC-CPPT trial results quantitatively matched predictions from the aggregate analysis.
- Baseline cholesterol levels accurately predicted IHD events in the LRC-CPPT placebo group, mirroring population studies.
Conclusions:
- Aggregate evidence strongly supports the lipid hypothesis, confirming cholesterol's causal role in IHD.
- Lowering total plasma cholesterol effectively reduces IHD risk in middle-aged hypercholesterolemic men.
- Findings suggest appropriate extrapolation of results to lower cholesterol levels, while emphasizing distinct evidence requirements for treatment programs.
Abstract:
Despite compelling evidence that elevated plasma total and low-density lipoprotein cholesterol plays a causal role in ischemic heart disease (IHD) (evidence derived from molecular biologic, genetic, animal experimental, and human observational studies), the results of individual clinical trials testing the lipid hypothesis have not been regarded as conclusive. Analyzed in aggregate, however, the trials results indicate a dose-response relationship between amount of cholesterol lowering and reduction of ischemic heart disease risk. This summary analysis predicted the quantitative measure of efficacy in the recently completed Lipid Research Clinics Coronary Primary Prevention Trial (LRC-CPPT). There was a quantitatively similar relationship between the amount of IHD risk reduction associated with amount of total plasma cholesterol reduction within the active drug (cholestyramine) treated group. Further, the risk function relating baseline level of total plasma cholesterol to ischemic heart disease incidence in community-based studies such as Framingham was so similar to the risk function of the LRC-CPPT placebo group that it accurately predicted the ischemic heart disease events in the trial. These findings in aggregate provide strong confirmation of the lipid hypothesis, indicate that lowering total plasma cholesterol in middle-aged hypercholesterolemic men will reduce ischemic heart disease risk, and suggest that some extrapolation of the results to lower levels of plasma cholesterol is appropriate. However, aggregate evidence that supports the lipid hypothesis should be distinguished from that required for intervention and treatment programs. Instituting the latter requires the review and evaluation of the evidence relating cholesterol levels and cholesterol reduction not only to ischemic heart disease, but also to other outcomes.(ABSTRACT TRUNCATED AT 250 WORDS)