High density lipoprotein

The high density lipoproteins (HDL, English High density lipoprotein) are those lipoproteins that transport free cholesterol and phospholipids from the body tissues to the liver.

Because HDL can carry out the removal of cholesterol from the arteries and transports it back to the liver for excretion, it is commonly known as good cholesterol or lipoprotein. >, giving a false idea that its high values can prevent certain diseases by itself, something not supported by conclusive scientific studies.

HDL are the smallest and most dense lipoproteins, they are composed of a high proportion of proteins. The liver synthesizes these lipoproteins as empty proteins and, after picking up cholesterol, they increase in size as they circulate through the bloodstream.

In each lipoprotein there are several peripheral apolipoproteins, in the case of HDL the main apolipoproteins are α-lipoproteins designated with the letter A.

Although some epidemiological studies, cited by certain publications and scientific articles, would show that high concentrations of HDL (greater than 60 mg/dL) have a protective character against cardiovascular diseases (such as ischemic heart disease and myocardial infarction); and, contrary to the fact that low HDL concentrations (below 35 mg/dL) would imply an increased risk of these diseases, none of these studies obtained scientifically consistent conclusions to support these statements. HDL level says very little about your health if taken in isolation, according to the same large studies done to date.

HDL levels are related to the degree of expression of the ATP-binding cassette transporter (ABCA1), whose expression is regulated by the action of micro RNAs. Overexpression of these produces a decrease in ABCA1 and consequently, decreased HDL levels.

There are 5 types of HDL subfractions identified. Large (more effective in removing cholesterol) and small (less effective), these types are 2a, 2b, 3a, 3b, and 3c.

Factors

Men tend to have significantly lower HDL levels than women. Physical activity, moderate alcohol consumption (red wine and to a lesser extent beer), estrogen treatments, vitamins E, C, B9 and the minerals Zn, Cu, Mg, and Se, and sexual activity, influence plasma HDL concentration. Hereditary forms such as familial hypercholesterolemia are also known. On the contrary, tobacco and leading a sedentary life decrease it.

Recommended range

The American Heart Association provides recommendations for raising HDL levels and reducing the risk of heart disease.^{[citation needed]}

A 2016 study published in the Science magazine reveals that some people have an alteration in a gene that prevents the functioning of the HDL cholesterol receptor in liver cells. The receptor in question is a protein known as SR-BI and that binds to HDL cholesterol circulating in the blood. People who have the mutation in the gene for this receptor are unable to absorb HDL in the liver, so its level increases a lot in the blood. Despite a high HDL, they have atherosclerosis and increased cardiovascular risk.