High-density lipoprotein is once considering as good cholesterol. Because it performs reverse cholesterol transport and expected to prevent heart disease.
High level of HDL-C indicates low chances for cardiovascular disease. Thus, it got the name good cholesterol (not that much good).
Why HDL is considering as good cholesterol? HDL removes cholesterol from atheroma in arteries. And returns to the liver for excretion or re-utilization thus called as good cholesterol.
HDL transports unused excess cholesterol from the cells to the liver or steroidogenic organs. The steroidogenic organs are adrenals, ovary, and testes. The steroidogenic organs use HDL cholesterol for the synthesis of steroid hormones.
High HDL levels may protect against cardiovascular diseases. In the other hand, low HDL levels may increase the chances of heart disease.
- Optimal more than 60 mg/dL (>1.55 mmol/dl)
- Borderline risk 40 to 60 mg/dL (1.03 to 1.55 mmol/dl)
- High risk less than 40 mg/dL (<1.03 mmol/dl)
Triglycerides in the HDL are not stable; thus degraded by hepatic lipase. These HDL particles become smaller and once again start cholesterol uptake from the cells. HDL cholesterol returned to the liver, excreted into the bile and later to the intestine.
Why people with infection has low HDL-C?
During an emergency (fight or flight), the adrenal gland needs HDL cholesterol to produce cortisone. Critical infection (sepsis) and severe inflammation (rheumatoid arthritis) consume a lot of HDL cholesterol. Thus, people with these condition has low HDL-C levels.
Is HDL Cholesterol Really Good? Not Always, Learn Why!
“Doubt Cast on the ‘Good’ in Good Cholesterol” published in The New York Times, May 16, 2012. The genetic information databases found high HDL-C has not reduced heart disease risk. People who inherit gene gives them natural high HDL-C levels throughout their life. Still, they have no less heart disease compared to others. If HDL-C is protective, then these people should not have heart disease or less heart disease.
High HDL-C levels does not mean enough HDL-P number. For example, larger HDL particle holds excess cholesterol, thus fewer particle numbers.
What is important? HDL cholesterol or particle number
HDL-P (particle number) and HDL-C (quantity of cholesterol) are different things. HDL-C is the cholesterol it contains; measured in milligrams/deciliter (mg/dL) or millimoles/liter (mmol/L). HDL-P is the numbers of HDL particles it contains; measured in a specific volume of blood.
Both HDL-C and HDL-P are important. HLD particle number confirms some particle working to remove unused cholesterol in the cells. HDL cholesterol should transform from small HDL particle to large HDL particle. This transformation confirms proper functioning of reverse transportation of cholesterol.
Transformation from small to large HDL particles confirms proper functioning of reverse cholesterol transport.
No transformation from small to large HDL particles indicates faulty reverse cholesterol transport. Thus, along with some HDL particle, the HDL particle size is also crucial. HDL particles can stay in plasma for about five days to transport cholesterol.
HDL particles number
HDL-P is the total number of HDL particles. HDL-P has a strong link to atherosclerosis & future CVD than HDL-C. Reference: Otvos et al. Circulation. 2006; 113:1556-1563
- Optimal: More than 34.9 µmol/L
- Borderline Risk: 35 to 26.7 µmol/L
- High: Less than 26.7 µmol/L
HDL particle size
HDL particle size is a marker for insulin resistance and metabolic syndrome.
- Optimal: More than 9.6 nm
- Borderline Risk: 9.6 to 8.9 nm
- High risk: Less than 8.9 nm
The large HDL particles number are lower in low HDL cholesterol and hypertriglyceridemia individuals.
- "Alterations of HDL subclasses in hyperlipidemic" published in Clinica Chimica Acta. 2003 Jun;332(1-2):95-102. The study shows HDL particle size in hyperlipidemic subjects shifted towards smaller sizes. This size shift indicates maturation of HDL may be abnormal in hyperlipidemic subjects.
- “Unique lipoprotein phenotype and genotype associated with exceptional longevity” published in the Journal of the American Medical Association 2003; 290: 2030–2040. The study shows individuals with exceptional longevity and their offspring have significantly larger HDL and LDL particles.
The protective effect of large HDL-P might explain by the free cholesterol accepting activity. The increased development of atherosclerosis is due to decrease in HDL particle size. And a general shift in HDL subspecies distribution toward small-size HDL.