High density lipoproteins (HDL) are a class of lipoproteins that carry cholesterol from the body's tissues to the liver.
Because HDL can remove cholesterol from the arteries, and transport it back to the liver for excretion, it is seen as a "good" lipoprotein. When measuring cholesterol, any contained in HDL particles is not a threat to the body's cardiovascular health. (In contrast to "bad" LDL cholesterol.)
HDL are the smallest and densest lipoproteins, and are composed of a high proportion of protein. The liver synthesises these lipoproteins as empty proteins and they pick up cholesterol and increase in size as the circulate through the bloodstream.
Men tend to have noticably lower HDL levels than women (men also have an increased risk of heart disease).
Epidemiological studies show that high concentrations of HDL (over 60 mg/dL) have protective value against cardiovascular diseases (such as ischemic stroke and myocardial infarction). Low concentrations of HDL (below 35mg/dL) are a positive risk factor for these diseases, especially for women.
The American Heart Association provides a set of guidelines for fasting HDL levels and risk for heart disease.
; Less than 40 mg/dL : Low HDL cholesterol, hightened risk for heart disease
; 40 to 59 mg/dL : Medium HDL level
; 60 mg/dL and above : High HDL level, optimal condition considered protective against heart disease