When cholesterol is discussed, majority of times it is discussed in terms of “good” or “bad”. Common understanding is HDL is "good cholesterol" and LDL is "bad cholesterol". However, cholesterol itself is essential to our life and it is very important to understand what it is and why our body needs it before thinking of "good" or "bad".
Cholesterol is a lipid that is synthesized or created by every cells in our body. Cholesterol is important because it creates foundation of our cells. If you remember from your biology class our cell has something called cell membrane. Cell membrane separates and protects interior of all cells from outside environment. Cell membrane contains cholesterol which keep the cell in fluid like structure rather than a solid block. It also allows transporters to set across the cell, which allows particles such as glucose, ketones, hormones and so on to enter the cell.
Cholesterol is also a precursor to hormones such as testosterone, estrogen, progesterone, cortisol and so on. Bile acid is also a form of cholesterol which is important for our digestion. Therefore, cholesterol is an essential to our body. So, if we didn’t have cholesterol, there won’t be a cell. And without cell, well, we won’t be alive.
However, not all cells can produce enough amount of cholesterol for its need, which is supported by other organs, such as liver, that can produce more cholesterol than it needs and transport it. To transport, our body mainly uses circulatory system (bloodstream), though it is not the only system available to transport.
Although we transport so many things in circulatory system such as, glucose, electrolytes, lactate without difficulty because they are water soluble, and our blood is made of plasma and protein which plasma is mainly water. As mentioned earlier, cholesterol is a lipid or fat which are not water soluble or hydrophobic. When substance is hydrophobic, it cannot transport through water, therefore, the body had to come up with way to transport cholesterol. The name of the vehicle to transport cholesterol is called lipoprotein. Lipoprotein is part protein and part lipid. Lipid side, which is hydrophobic, binds to cholesterol and protein side, which is hydrophilic, would repel water so that it can transport cholesterol through blood.
HDL, LDL, VLDL is not referring to types of cholesterol. They refer to density of the lipoprotein that binds to cholesterol so it can transfer through bloodstream. HDL is high density lipoprotein; LDL is low density lipoprotein and VLDL is very low-density lipoprotein. In other words, cholesterol itself is same, however, the density of the lipoprotein is different.
Therefore, there is no such thing as “good” or “bad” cholesterol. It is the characteristics of HDL, LDL, VLDL that has positive or negative influence over our health.
Kota Shimada
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