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Cholesterol is usually divided into good and bad varieties, with bad one linked to high risk of heart problems. New data suggest that the picture is more complex, and good cholesterol can be converted into an abnormal variety capable of damaging heart.

We all heard about cholesterol. Most people are well aware of connection between high level of cholesterol and heart problems. Cardiovascular diseases are the single largest cause of mortality in Western world, and most of these diseases are closely connected with the dis-balance of cholesterol in the body.

Cholesterol is not necessarily bad. After all, this is one of the major components of our cell membranes. Our body simply won’t be able to function without cholesterol. Every day our body produces, on average, 1g of cholesterol to cover its needs in this biochemical compound.  Problems come with the excess level of this essential biochemical in the blood. 

High level of blood cholesterol is traditionally considered as a risk factor for the development of various heart problems and problems with blood vessels elsewhere in the body.

Essentials of cholesterol metabolism

Cholesterol in our body originates from two major sources. It is produced by various organs and tissues in our body (for example, liver), and it also comes from our food. In people with healthy diet, food contributes to around 20% of all cholesterol. Obviously, unhealthy diet has a potential of increasing the cholesterol intake rather significantly. But what actually happens when the blood cholesterol rises to the dangerous levels?

Cholesterol is needed by each and every cell in the body. This means that it has to be delivered to all these cells from where it is produced or ingested. Also, the excess of cholesterol should be properly removed (this task is fulfilled by the liver as well) and disposed of. Cholesterol molecules must be able to travel around the body.

There is one problem here, however. Cholesterol is not soluble in water. If you take chemically pure solid cholesterol and try to mix it in a glass of water, it will simply precipitate to the bottom of the glass. Insolubility of cholesterol means that it is also not soluble in blood. And this creates problems with its transportation around the body.

Our body solved the problem by providing cholesterol with special carrier proteins in the blood plasma. These proteins are capable of binding cholesterol molecules on their surface and transporting them in the blood around the body. The binding is reversible, and cholesterol molecules can be released when they reach their destination.

“Good” cholesterol and “bad” cholesterol

Many of us heard of so-called good and bad cholesterol. Well, the names are slightly confusing. There is no chemical difference between these two types of cholesterol, both are exactly the same compound. The difference is in the type of carrier protein to which cholesterol is bound. Our blood contains two major type of cholesterol transporter – High Density Lipoproteins (HDL) and Low Density Lipoproteins (LDL).

Cholesterol bound to the HDLs is considered good, and cholesterol bound to the LDLs is regarded as bad.

Why? Because HDL binds cholesterol quite tightly which enables it to be successfully delivered to its destination, while LDLs are not very good at keeping cholesterol molecules and tend to lose them during transportation. Once free cholesterol is released from LDL, it becomes insoluble and precipitates on the walls of blood vessels.

For some reason, the precipitation of cholesterol is particularly active on the walls of blood vessels supplying our heart. It can also be deposited on the walls of aorta and in the blood vessels of the brain. Deposits of cholesterol are known as cholesterol plaques. Over time, these plaques grow and start to block the affected blood vessels. This eventually leads to the lack of blood supply to various tissues and organs, which start to suffer from the lack of oxygen and nutrients. Ischemic heart disease, aortic aneurism, stroke and myocardial infarction are all caused by formation of cholesterol plaques. LDL-bound “bad” cholesterol is considered the major villain in their development.

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