Cholesterol is a frequent topic of conversation when it comes to health risks. Oftentimes cholesterol is solely viewed as detrimental to health. The fact is, however, that cholesterol is an absolute requirement for every cell in the body. A number of important molecules in the body are synthesized from the cholesterol molecule including the sex hormones, components of bile and vitamin D. As it pertains to overall health, one of the signature problems with cholesterol arises depending upon how much of it is being transported through the bloodstream by a specific type of carrier complex.
The Body Regularly Synthesizes Cholesterol
As the name indicates, cholesterol is a “sterol,” and is a waxy, fat-like substance. Chemically it is a multi-ringed molecule that is largely insoluble in water. Every cell requires cholesterol as a critical component of the cellular membranes, the cholesterol molecules changing the relative “fluidity” of the membrane. The human body can synthesize a significant fraction of the cholesterol that it requires for optimal functioning, the liver and intestines being major sites of synthesis. However, some cholesterol must be obtained through the diet.
Transport of Cholesterol in the Bloodstream
Given the limited solubility of cholesterol in aqueous solutions (that is water based solutions), it cannot be efficiently transported on its own throughout the body via the circulatory system. The body uses specific carrier complexes containing what are known as “lipoproteins” to transport cholesterol through the blood and to organs that need it. There are several classes of these complexes found in the bloodstream and they are identified based on their density, which reflects the relative proportions of lipids, cholesterol and carrier proteins. These complexes are known as “VLDL” for very low density lipoprotein, “IDL” for intermediate density lipoprotein, “LDL” for low density lipoprotein, and finally “HDL” for high density lipoprotein.
Why is Some Cholesterol “Good” and Some “Bad”
When a person has their serum cholesterol levels measured, different types of values are usually reported. These include total serum cholesterol, LDL cholesterol and HDL cholesterol. For the latter two measurements, LDL is often referred to as “bad” cholesterol while HDL is referred to as “good” cholesterol. Both of these lipoproteins carry cholesterol in the bloodstream. A major difference between them, however, is that they behave very differently when it comes to how and where they deposit the cholesterol molecules they are carrying. HDL, for instance, can transport cholesterol molecules from other organs back to the liver where the cholesterol can be expelled from the body. LDL, on the other hand, can offload its cargo of cholesterol in bad places, such as on the lining of the blood vessels.
The interactions that take place between these carriers of cholesterol and specific cell types are quite numerous. And there is much that is still to be learned about how they behave. What does appear to be relatively clear is that the more LDL cholesterol that is in a person’s blood, the greater chance that they will deposit this cholesterol in plaques found in the arteries. HDL is able to gather cholesterol from cells, delivering it to the liver and also contains specific proteins that can act on lipids in LDL particles to prevent their oxidation. The oxidation of the lipids in LDL particles makes them more likely to stick to and worsen arterial plaques. Clearly, as far as health and cholesterol is concerned more HDL is better. Oftentimes, a physician will report the ratio of total cholesterol to HDL cholesterol to a patient. A ratio of 4 or below is considered optimal.
To learn much more about the biochemistry of cholesterol visit the Medical Biochemistry page. To learn more about ways to increase your levels of “good” HDL cholesterol visit this informative site at the Mayo Clinic.
Kenneth Rosen - I am a medical research doctor with more than 20 years of experience studying how the nervous system and skeletal muscle develop and ...
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