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A lipoprotein is often a combination of lipids (fats) and proteins, and one example of these is high-density lipoprotein (HDL). These work to transport cholesterol and are also called good cholesterol due to their properties. Higher amounts of high-density lipoprotein frequently correspond to a reduced incidence of cardiac disease, while lower amounts have been associated with greater likelihood of certain cardiac diseases occurring.
In humans, the most desirable high-density lipoprotein is above 60 milligrams per deciliter (mg/dL). Anything below 40 mg/dL is likely to increase the chances that people will develop some sort of heart disease. The issue of density typically refers to amount of protein in each molecule. A denser molecule has higher protein levels. In contrast, low-density lipoprotein (LDL) means a much smaller amount of protein in the molecule, and this deficit may be part of why LDL is called the "bad cholesterol."
HDL tends to be directly involved in removal of cholesterol to the liver and a few other areas for processing. Higher amounts of high-density lipoprotein can thus explain its use in reducing cardiac risk. Quicker removal of cholesterol to the liver means less likelihood that cholesterol will attach to the insides of blood vessels, building up plaque and eventually causing conditions like atherosclerosis.
From the outside of the body, it’s very hard to tell the levels of high-density lipoprotein, though a strong guess might be made that levels are low if a person has diagnosed conditions like atherosclerosis. Usually, real testing must occur by analyzing blood, since this where HDL is located. Taking cholesterol levels with a simple blood test may measure HDL, LDL, triglycerides and total cholesterol. Low levels of HDL almost always have correspondingly higher levels of LDL, and it's believed HDL helps to reduce LDL. This is another reason why high-density lipoprotein is considered “good.”
If a cholesterol test does show less than desirable amounts of high-density lipoprotein, people may be given advice on how to increase levels. These could include changing to a healthier diet, getting plenty of exercise, losing weight, and ceasing smoking. Certain foods should be avoided, such as any foods with trans fats.
If total cholesterol levels do not improve, doctors might consider asking people to take medications that are cholesterol reducers. Sometimes people have a higher inherited risk of having high cholesterol. They won’t respond to basic lifestyle interventions and might only raise HDL levels through drugs targeted at lowering all cholesterol levels or at lowering LDL.