High-density lipoprotein

[1] Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells.

[2] HDL particles are commonly referred to as "good cholesterol", because they transport fat molecules out of artery walls, reduce macrophage accumulation, and thus help prevent or even regress atherosclerosis.

[8][needs update] Higher native HDL levels are correlated with lowered risk of cardiovascular disease in healthy people.

[2] HDL transports cholesterol mostly to the liver or steroidogenic organs such as adrenals, ovary, and testes by both direct and indirect pathways.

[2] Several steps in the metabolism of HDL can participate in the transport of cholesterol from lipid-laden macrophages of atherosclerotic arteries, termed foam cells, to the liver for secretion into the bile.

This pathway has been termed reverse cholesterol transport and is considered as the classical protective function of HDL toward atherosclerosis.

For example, HDL and its protein and lipid constituents help to inhibit oxidation, inflammation, activation of the endothelium, coagulation, and platelet aggregation.

Studies confirm the fact that HDL has a buffering role in balancing the effects of the hypercoagulable state in type 2 diabetics and decreases the high risk of cardiovascular complications in these patients.

Also, the results obtained in this study revealed that there was a significant negative correlation between HDL and activated partial thromboplastin time (APTT).

[citation needed] Epidemiological studies have shown that high concentrations of HDL (over 60 mg/dL) have protective value against cardiovascular diseases such as ischemic stroke and myocardial infarction.

[19][non-primary source needed] Very high HDL-C levels (≥80 mg/dL in men, ≥100 mg/dL in women) appears to be detrimental to cardiovascular outcomes.

Several genetic conditions cause abnormally low or high HDL-C levels, often without the expected change in cardiovascular disease rates.

[29] As technology has reduced costs and clinical trials have continued to demonstrate the importance of HDL,[30] methods for directly measuring HDL concentrations and size (which indicates function) at lower costs have become more widely available and increasingly regarded as important for assessing individual risk for progressive arterial disease and treatment methods.

[31] The HDL particle concentrations are typically categorized by event rate percentiles based on the people participating and being tracked in the MESA[32] trial, a medical research study sponsored by the United States National Heart, Lung, and Blood Institute.

[2] HDL lipoprotein particles that bear apolipoprotein C3 are associated with increased, rather than decreased, risk for coronary heart disease.

As there is some evidence that the HDL reduction is caused by increased reverse cholesterol transport, it is unknown if AR agonists' HDL-lowering effect is pro- or anti-atherogenic.

[63][64] A randomized clinical trial demonstrated that treatment with niacin can significantly reduce atherosclerosis progression and cardiovascular events.

[66] Both fibrates and niacin increase artery toxic homocysteine, an effect that can be counteracted by also consuming a multivitamin with relatively high amounts of the B-vitamins, but multiple European trials of the most popular B-vitamin cocktails, trial showing 30% average reduction in homocysteine, while not showing problems have also not shown any benefit in reducing cardiovascular event rates.

[68] Lovaza has been shown to increase HDL-C.[69] However, the best evidence to date suggests it has no benefit for primary or secondary prevention of cardiovascular disease.