LDL and HDL Cholesterol

Lipoproteins are the carriers of lipids in the blood. They are named chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) on the basis of their components, size & density.

Low density lipoproteins are also known as "bad cholesterol." High density lipoproteins are sometimes called "good cholesterol." The reasons will become obvious below.

How LDL & HDL are formed

Lipids in the diet are digested & absorbed into the blood in the form of free fatty acids and chylomicrons. Chylomicrons are composed of protein, phospholipid, cholesterol & triglycerides. Liver breaks down the remains of chylomicron & other lipids, to produce VLDL (very low density lipoprotein). 

The VLDL, while circulating loses some of their triglycerides to the fat depots & is ultimately converted into LDL (low density lipoprotein). The LDL’s are again taken up by the lever & degraded. The LDL is also taken up by a kind of defense cells called Macrophages, which are then converted into foam cells and become instrumental for development of clogging of arteries. After degradation of LDL inside the cells, the lipids are packed in HDL.

How dangerous is cholesterol?

Fats including cholesterol cannot dissolve in the blood or water. So they bind to the lipoproteins to travel in the body.

LDL cholesterol is considered as ‘bad’ cholesterol. Because, elevated levels of LDL cholesterol combined with other fats tends to get attached in the inner walls of the arteries which will reduce the inner dimensions of the arteries causing raise in blood pressure in the initial stages. It may clog the whole artery sometimes, making the blood flow almost impossible.

Sometimes, these deposits may get detached from the wall & run in the blood. They get blocked in smaller vessels, completely cutting off the supply to that particular organ. For example, if this plaque blocks the blood flow to the heart, it causes heart attack and failure, when it get blocked in an artery that supplies the brain, ends up in a stroke.

On the other hand, HDL cholesterol is the good variety of fat, as it does not allow adhesion of harmful cholesterol in arteries & reduces the incidences of heart attack & strokes. Having too less of concentration of HDL also increases the risk of heart failure.

Triglycerides: Elevated triglycerides often have a high total cholesterol lever especially high LDL & low HDL concentrations.

Lp (a) cholesterol: It is similar form of LDL cholesterol with significant risks for the development of clogs in the arteries.

Hence, the ratio of LDL & HDL concentration is important to assess the risk of heart & vascular diseases.

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