High density lipoprotein overview
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High Density Lipoprotein Microchapters |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aarti Narayan, M.B.B.S [2]; Raviteja Guddeti, M.B.B.S. [3]
Overview
High-density lipoproteins form a class of lipoproteins, varying somewhat in their size (8–11 nm in diameter), that carry cholesterol from the body's tissues to the liver. About thirty percent of blood cholesterol is carried by HDL.[1]
It is hypothesized that HDL can remove cholesterol from atheroma within arteries and transport it back to the liver for excretion or re-utilization— which is the main reason why HDL-bound cholesterol is sometimes called "good cholesterol", or HDL-C. A high level of HDL-C seems to protect against cardiovascular diseases, and low HDL cholesterol levels (less than 40 mg/dL) increase the risk for heart disease. When measuring cholesterol, any contained in HDL particles is considered as protection to the body's cardiovascular health, in contrast to "bad" LDL cholesterol.
Most clinical trials on prevention of coronary artery disease focus on lowering the levels of LDL cholesterol in the blood using statins and other lipid lowering drugs. These have shown improved clinical outcomes and reduction in mortality.
However, a causal relationship between low HDL cholesterol levels and development of significant coronary artery disease has not been established. There is a lack of evidence for proving that raising HDL levels can reduce cardiovascular events in those with coronary artery disease. Statins are used in treatment of patients with low HDL levels to reduce the levels of "bad" LDL cholesterol in the blood [2] [3].
Causes
High density lipoprotein (HDL) is considered "good cholesterol" as its levels are inversely proportional to CAD. It is regarded a positive cardiac risk factorif the levels are below 35 mg/dL or total cholesterol to HDL ratio in > 5.0 (in men) or total cholesterol to HDL ratio in > 4.5 (in women). When the levels are above 60 mg/dL it is considered negative cardiac risk factor.
Epidemiology and Demographics
Epidemiological studies have shown that high concentrations of HDL (over 60 mg/dL) have protective value against cardiovascular diseases such as ischemicstroke and myocardial infarction. Low concentrations of HDL (below 40 mg/dL for men, below 50 mg/dL for women) are a positive risk factor for these atherosclerotic diseases.
Data from the landmark Framingham Heart Study showed that for a given level of LDL, the risk of heart disease increases 10-fold as the HDL varies from high to low. Conversely, for a fixed level of HDL, the risk increases 3-fold as LDL varies from low to high.
Low HDL and Cardiovascular Risk
The plasma levels of HDL are inversely proportional to the development of coronary artery disease (CAD) making HDL a negative cardiac risk factor.[4] Low serum HDL-cholesterol can be an isolated abnormality or can be associated with hypercholesterolemia. Patients with premature coronary artery disease, defined as CAD in men less than 55 to 60 years of age and women less than 65 years of age, have a primary reduction in HDL-cholesterol. Studies have shown that low HDL risk is independent of the risk attributed to elevated LDL-cholesterol (low density lipoprotein) in the serum. Findings from large scale prospective studies indicate that for every 1 mg/dL rise in serum HDL levels the risk of CAD reduces by 2% to 3% in men and women respectively.
References
- ↑ http://www.americanheart.org/presenter.jhtml?identifier=180
- ↑ Rubenfire M, Brook RD (2013). "HDL cholesterol and cardiovascular outcomes: what is the evidence?". Current Cardiology Reports. 15 (4): 349. doi:10.1007/s11886-013-0349-3. PMID 23420445. Unknown parameter
|month=ignored (help) - ↑ Ginter E, Simko V (2013). "New promising potential in fighting atherosclerosis: HDL and reverse cholesterol transport". Bratislavské Lekárske Listy. 114 (3): 172–6. PMID 23406187.
- ↑ Rajagopal G, Suresh V, Sachan A (2012). "High-density lipoprotein cholesterol: How High". Indian J Endocrinol Metab. 16 (Suppl 2): S236–8. doi:10.4103/2230-8210.104048. PMC 3603035. PMID 23565387. Unknown parameter
|month=ignored (help)