Bad Cholesterol (LDL) And Good Cholesterol (HDL): Learn The Difference
To say that there is good and bad cholesterol is an oversimplification of the role of lipoprotein carriers. Cholesterol builds up in the arteries and promotes the formation of fatty plaques or aneurysms, leading to atherosclerosis.
HDL and LDL cholesterol are the lipoproteins that carry cholesterol in the blood. HDL is high-density lipoprotein (HDL stands for high-density lipoprotein) and LDL is low-density lipoprotein (LDL stands for low-density lipoprotein).
This classification of lipoproteins is due to the technique used to separate them: ultracentrifugation. In this technique, the plasma in a test tube is centrifuged at high speed and separated according to the density of the lipoproteins, leaving the most dense (HDL) at the bottom of the tube and the least dense (LDL and other lipoproteins) floating at different levels in the tube.
Cholesterol is a lipid molecule that is insoluble in water. Lipoproteins are spherical particles composed of proteins and lipids that carry cholesterol and other lipids in the blood. The main lipoproteins transported by cholesterol are HDL and LDL.
What is HDL-cholesterol?
HDL or HDL-cholesterol (HDL-C) are the lipoproteins that transport cholesterol from the cell membranes to the liver. They are also known as good cholesterol, although this is incorrect, as HDL contains more than just cholesterol.
Origin of HDLs
HDLs are derived from the Apo A1 protein, which is synthesized in the extracellular space. This protein circulates through the tissues by capturing cholesterol and phospholipids from the membrane, and once in circulation, it exchanges protein and cholesterol esters with other lipoproteins.
Characteristics of HDL
- A higher percentage of protein than fat.
- Densities between 1,063 and 1,210 g/ml.
- The diameter is between 70 and 120 angstroms, making it the smallest lipoprotein.
Functions of HDL
The main function of all lipoproteins is to dissolve fat in the blood. HDL is the lipoprotein responsible for transporting cholesterol from extrahepatic tissues to the liver. This is called reverse cholesterol transport.
In the liver, cholesterol is converted to bile acids, which are excreted or recycled by the intestines.
HDL values in human blood
High levels of HDL cholesterol are associated with the prevention of cardiovascular disease (CVD). Normal HDL values for adults should be 40-60 mg/dL (SI units of 1.04-1.55 mmol/L). values above 60 mg/dL are recommended for the prevention of CVD. HDL values below 40 mg/dL are a high risk for cardiovascular disease.
What is LDL cholesterol?
LDL or low-density lipoprotein cholesterol (LDL-C) is a lipoprotein that transports cholesterol from the liver to extrahepatic tissues. They are also known as bad cholesterol because high levels of this lipoprotein can be deposited in the arteries and create atherosclerotic plaques.
Sources of LDL
LDLs originate from VLDLs (very low density, bulky, triglyceride-rich lipoproteins) that are formed in the liver. These VLDLs travel through the bloodstream, carrying triglycerides to the tissues, reducing their size and increasing their cholesterol levels until they become LDLs.
Characteristics of LDLs
- A higher percentage of lipids than proteins.
- Densities between 1.019 and 1.063 g/ml.
- Diameter is approximately 250 angstroms.
- The characteristic protein of LDL is Apo lipoprotein B100.
LDL is responsible for transporting cholesterol to the tissues that need it. VLDL, which contains triglycerides and cholesterol, is assembled by the liver. Triglycerides are released as they circulate in the bloodstream. LDLs are the result of a reduction in the size of these VLDLs.
The apo B100 protein of LDLs binds to cellular receptors and enters the cell by endocytosis. The cells can then use the cholesterol to form membranes and other compounds.
LDL values in human blood
High levels of LDL cholesterol are associated with cardiovascular disease (CVD). Optimal LDL values for adults should be less than 100 mg/dl (less than 2.6 mmol/L, SI). Values between 130-159 mg/dl (3.36-4.11 mmol/L, SI) are borderline risk for CVD, while values above 159 mg/dl are extreme risk. This person is at high risk for cardiovascular disease.
Good and bad cholesterol
Cholesterol is an important molecule for the function of cells and animal organisms. This compound is a precursor to steroid hormones, such as sex hormones and corticosteroids. It is also part of the cell membrane, sandwiched between the phospholipids of the lipid bilayer, which regulate membrane fluidity.
To say that there is good and bad cholesterol is an oversimplification of the role of transporting lipoproteins. Cholesterol builds up in the arteries and promotes the formation of fatty plaques or aneurysms, leading to atherosclerosis.
The lipoproteins that transport cholesterol in the arteries (LDL) are misnamed bad cholesterol, while the lipoproteins that take up cholesterol from the membranes (HDL) are nicknamed good cholesterol.