Heart disease and stroke are the two main causes of disease and death in the developed world, according to Michael Pignone, M.D., chief of the department of medicine at the University of North Carolina. Risks for these two diseases include factors that people can change and those they cannot. The level of lipids, or fat, in the blood is a factor that can be changed, and HDL cholesterol is key in doing so.
Definition
People get their lipids from food, but they are also made in the liver. They are carried throughout the bloodstream inside structures called lipoproteins. Scientists categorize lipoproteins based on their size and their density, or the amount of lipids and proteins they contain. "HDL" is short for "high-density lipoprotein."
Function
High-density lipoproteins are responsible for getting cholesterol from the other lipoproteins and the tissues, then taking the cholesterol to the liver in a process called reverse cholesterol transport. Cholesterol then leaves the liver in a substance called bile.
Significance
HDL is called the "good" cholesterol because it carries cholesterol from the tissues to the liver so it can be removed from the body, as explained in "Harper's Illustrated Biochemistry" by Kathleen Botham, Ph.D. If there are high levels of cholesterol in the bloodstream, the cholesterol will deposit in the walls of the arteries and develop into areas called plaques. Plaques cause atherosclerosis, or the hardening of the arteries, and make the inside of the artery smaller. This makes it hard for the red blood cells to pass through and can lead to stroke. HDL works against this process.
Evaluation
Routine cholesterol screening is recommended for all adults, because high levels of LDL, or low-density lipoprotein, are a major risk factor for heart disease and stroke. Since HDL helps eliminate LDL from the body, high HDL levels -- 40 mg per deciliter or above -- are desirable. A simple blood test can measure HDL, LDL, triglycerides and total cholesterol.
Treatment
Treatment for high cholesterol is based on the level of LDL, or "bad" cholesterol. After high LDL levels have been addressed, the patient can work on increasing HDL levels if necessary. The initial approach is to increase the amount of exercise. If exercise alone is not effective, the physician may prescribe niacin, gemfibrozil or clofibrate.
References
- "Current Medical Diagnosis & Treatment 2011"; Stephen McPhee, M.D., Maxine Papadakis, M.D.; 2011
- "Harper's Illustrated Biochemistry"; Robert Murray, M.D., Ph.D., David Bender, Ph.D., Kathleen Botham, Ph.D. et al.; 2009
- The Merck Manual for Healthcare Professionals: Lipid Disorders
