Contrary to what many think, HDL as well as other lipoproteins are not made up of "pure cholesterol"; in fact, they also contain various specific proteins necessary for their function, ie the transport of some fats in the blood.
There are various types of lipoproteins and they all have a specific metabolic role; none of them can be considered useless or evil, even if alterations of their structure, of their quantity and of their percentage on the total lipoproteins can cause a disease condition and facilitate the onset of other very serious pathologies.
By transporting cholesterol from the periphery to the liver and reducing its deposit in the arteries - a predisposing factor for "atherosclerosis - HDLs are considered beneficial and therefore are referred to as" good cholesterol. "In practice, they act as a" scavenger "of cholesterol.
LDL, on the other hand, by channeling cholesterol towards the peripheries and, if in excess, by promoting its deposit in the arteries - thus raising the risk of atherosclerosis - are potentially harmful and for this reason they are defined as "bad cholesterol".
For further information: VLDL, LDL, HDL: How Many Names Does Cholesterol Have?
HDL is measured by analyzing the relative concentration in the blood serum. They are not all the same and there are different types, which vary in shape, size and chemical composition. The most effective in "cleaning" the arteries are logically the most active in the exchange of lipids with cells and other lipoproteins.
HDL and LDL lipoproteins are considered strong indicators of cardiovascular risk, both individually assessed and in relation to the relationship between them and total blood cholesterol; in fact, the reduction of HDL and the increase of LDL always exert a negative effect.
It is possible to increase HDL and reduce LDL (in an absolute or percentage way) by correcting the diet and increasing physical exercise. The diet, in particular associated with motor activity and possibly certain supplements, allow to significantly modify the lipid profile and the consequent cardiovascular risk.
. Clinically, HDL (High-Density Lipoprotein) are classified as high-density lipoproteins. Lipoproteins are particles containing specific apolipoprotein units, necessary for the exchange and transport of fats (cholesterol, phospholipids, triglycerides, etc.).
There are various types of apolipoproteins; both the number and the type of apolipoprotein distinguish the various lipoproteins. The typical apolipoprotein of HDL is Apo A1.
Lipoproteins have a hydrophilic surface (similar to water) and serve to convey lipids into the blood plasma (aqueous matrix). This function is very important, since fats do not dissolve normally in water and tend to aggregate forming "oily bubbles" (as happens by putting oil in water).
There are 5 different types of lipoproteins, all with different functions and characteristics:
- Chylomicrons: transport fats from the intestine (which absorbs them with digestion) to muscle cells and adipose tissue
- VLDL: mainly carry triglycerides from the liver to adipose tissue
- IDL: they are intermediate between VLDL and LDL (not detectable in healthy subjects)
- LDL: carry cholesterol from the liver to peripheral cells
- HDL: carry cholesterol from peripheral cells to the liver to steroidogenic organs (responsible for the synthesis of steroid hormones, such as cortisol and sex hormones).
The metabolism of HDL is closely correlated with that of LDL, even in the VLDL form.
Each HDL is made up of 80-100 specific proteins, which make it capable of carrying even several hundred fat molecules at a time. The "replenishment" and "unloading at destination" of fats occur through the interaction of HDL with cells and other lipoproteins.
It is a steroid lipid that the organism is able to produce autonomously and to assume through food. Its function in the organism is multiple:
- Structural and vehicle in cell membranes
- Precursor of steroid hormones
- Precursor of vitamin D.
- Ingredient of bile juices, important for digestion.
Cholesterol circulates within the bloodstream in a form linked to lipoproteins; if it were free, it would aggregate forming potentially harmful or lethal thrombus.
The excess of cholesterol in the blood (for genetic or environmental causes) can be harmful, due to the tendency to settle in the arteries; it is the first step towards the formation of an atherosclerotic plaque.
However, it should be remembered that the tendency to deposit varies according to the lipoprotein that transports it: LDLs are the harmful ones (they bring cholesterol to the peripheries), while HDLs are the beneficial ones (they bring cholesterol to the organs that metabolize it).
) from the liver to the tissues.
HDLs are initially very small and carry fat from the periphery to the organs. They increase in size and decrease in density with the incorporation of fats.
Each lipoprotein contains:
- A completely different number and type of Apo Proteins
- An equally different quantity and variety of lipids.
HDLs mostly contain ApoA1. Compared to LDL and VLDL, they are distinguished by:
- Higher percentage of protein
- Lower percentage of cholesterol
- Lower percentage of triglycerides
- Higher percentage of phospholipids.
All these characteristics contribute to determining the higher density of HDLs.
of total cholesterol, LDL and triglycerides, then applying the Friedwald formula:
HDL cholesterol = total cholesterol - [LDL cholesterol + (triglyceridemia / 5)].
For further information: HDL Cholesterol Calculation
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