Doctors measure the levels of high-density lipoprotein, or good, cholesterol, and low-density lipoprotein, or bad, cholesterol, in your blood to assess your risk for heart disease. While it is convenient to label HDL and LDL as "good" or "bad," having a high level of HDL in your blood does not necessarily decrease the negative impact of having a high level of LDL. You should consider the ratio of your HDL to LDL levels in addition to other risk factors to accurately assess your risk for heart disease.
Cholesterol and Atherosclerosis
LDL carries cholesterol from your liver out to body tissues for use. HDL does the opposite: It scavenges cholesterol from your body tissues and takes it back to your liver for removal. If your LDL values are high, some of the cholesterol ends up being deposited as plaques in your arteries, causing them to harden. The hardening of arteries is known as atherosclerosis and increases your risk of having a heart attack or stroke.
LDL as the Primary Target
Although high HDL levels protect the heart, treatments for high cholesterol focus primarily on lowering LDL cholesterol. The National Cholesterol Education Program has singled out LDL as the primary target of therapy as both epidemiological and clinical research strongly support its role in development of atherosclerosis. Not all of the protective value of HDL can be accounted for by its role in removing cholesterol from arteries. NCEP reports that 50 percent of variance in HDL levels can be attributed to external factors, such as activity level. Some of the heart protection associated with high HDL levels can be attributed to other beneficial effects of a healthy lifestyle but not the direct action of the molecule itself.
High HDL vs. High LDL
Dr. Peter Cohn writes in "The Clinical Advisor" that the answer to the question of whether a high HDL value counterbalances a high LDL value is not straightforward, as it depends on factors such as whether you have coronary artery disease and your other risk factors. According to a 2002 report from NCEP, smoking, being overweight or obese, having Type 2 diabetes, having a family history of heart disease and eating a diet high in saturated fat all increase your risk of heart disease.
The Ratio of LDL to HDL
A 2008 study published in the "Journal of the American College of Nutrition" details the effectiveness of using a ratio of LDL to HDL as a tool for assessing heart disease risk. The authors note that this ratio is more effective at predicting heart disease risk than LDL alone. The power of the LDL:HDL ratio comes from the fact that it takes into account the two-way traffic of cholesterol in the arteries. There is no current standard for an optimal ratio of LDL to HDL, but the authors conclude that the risk of death from heart disease appears to increase significantly at a ratio 3.5:3.7.
References
- "Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) Final Report"; National Cholesterol Education Program; September 2002
- American Heart Association; Good vs. Bad Cholesterol; Jul. 21, 2010
- "The Clinical Advisor"; Advisor Forum: When to Treat High LDL with High HDL; P. Cohn, Apr. 20, 2009
- "Journal of the American College of Nutrition"; The LDL to HDL Cholesterol Ratio as a Valuable Tool to Evaluate Coronary Heart Disease Risk; N. Fernandez, et al.; February 2008
