3D representation of a Cholesterol Molecule

Cholesterol – Function, Production, Statins, & Types

What is Cholesterol?

So what is cholesterol in the first place? Well, cholesterol is a waxy, fat-like substance that is found throughout the body as a major building block of our cells.

Cholesterol is a type of lipid; lipid referring to molecules that are biological in origin and that are also soluble in non-polar solvents, like oil. Lipids are substances like fats, waxes, sterols, fat soluble vitamins, monoglycerides, diglycerides, triglycerides, phospholipids, etc.

Why Do We Need Cholesterol?

Cholesterol is synthesized by the cells of all types of animal, and is an essential structural component of animal cell membranes. The cell membrane is composed of 25-30% cholesterol, and cholesterol maintains the structural integrity and membrane fluidity of a cell for a whole range of temperatures. Notice that because animal cells use cholesterol in their cell membrane, they do not need to build a cell walls like plants and some bacteria to maintain cell structure.

cholesterol packing with phospholipids in cell membrane
Cholesterol molecules packs into cell membranes to reduce permeability to water-soluble molecules.

Cholesterol also reduces the permeability of lipid membranes. Specifically, cholesterol helps to restrict the passage of molecules through the cell membrane by increasing the packing of phospholipids that make up the cell membrane. Cholesterol fits into the spaces between the phospholipids and prevents water-soluble molecules from diffusing across the membrane.

Cholesterol also plays a role in endocytosis, which is a form of active transport where cells transports molecules via engulfing them. One example of active transport is when vesicles transports molecules into and out of cells.

Cholesterol is a required ingredient for the synthesis of vitamin D, bile salts, and all steroid hormones; including (but not limited to) cortisol, aldosterone, progesterone, estrogen, testosterone, and their derivatives.

Cholesterol also assists in the formation of lipid rafts in the plasma membrance. Lipid rafts are responsible for bringing receptor proteins closer in proximity to secondary messenger molecules.

Furthermore, cholesterol and phospholipids are both electrical insulators, and are used as such as major building block for myelin sheaths. The function of a myelin sheath is to increase the transmission speed of electrical signals through nerve fibers. Without myelin sheaths, or when the myelin sheath dysfunctions, you get issues such as multiple sclerosis.

Cholesterol Production & Statins

blood cells floating in vein
Blood plays many roles with Cholesterol. Cholesterol absorbed from food is carried by the blood stream, and cells can absorb cholesterol from the blood. Cholesterol is also required for the produciton of heme, a key component of hemoglobin. Which without, our red blood cells couldn’t carry oxygen through the body.

About 20% of total daily cholesterol is produced in the liver; other sites that produce cholesterol in high amounts includes the intestines, adrenal glands, and reproductive organs.

Cells can obtain cholesterol from 2 sources. Cholesterol can be absorbed from the surrounding environment, and cholesterol can be synthesized from acetyl-CoA through the mevalonate pathway.

We can absorb cholesterol from the food that we eat. Cells may also uptake cholesterol from the blood stream through endocytosis. This is significant because if cholesterol production is halted (through the use of statins for example), then the cells adapt by absorbing cholesterol from the blood.

On the other hand, the synthesis of cholesterol in the body goes through something called the mevalonate pathway, which is a series of biochemical reactions that are required for the production isoprenoids. Example of some isoprenoids includes cholesterol, the heme-A, vitamin K, coenzyme Q10, dolichol, isopentenyl tRNA, ubiquinone and all steroid hormones.

Cholesterol is an essential building block of cell membranes. Heme is required for hemoglobin- for the function of red blood cells to absorb & carry oxygen throughout the body. Vitamin K is required for the blood’s ability to clot and for binding calcium to the bones. And ubiquinone (fully reduced CoQ-10) is required for the proper function of mitochondria, the powerhouse of a cell.

The Consequence of Statin Usage

Understanding the function of the mevalonate pathway is important when trying to lower cholesterol through drugs like statins. Statins lower cholesterol by stopping the production of mevalonate by inhibiting the HMG-CoA reductase enzyme.

10mg Rosuvastatin Crestor brand
By Mk2010 (Own work) [CC BY-SA 4.0], via Wikimedia Commons Statins are double edged swords. Although they may provide cardiovascular protection, they may damage the body in other areas.
Although there is evidence showing that statins are effective for treating and/or preventing cardiovascular disease, statins may pose many serious side effects. Such as increased in muscles pain & muscle damage, and increases risk of developing diabetes mellitus.

And I don’t really understand how statins in the long run benefit cardiovascular diseases if they reduce beneficial substances in the body that directly benefit the cardiovascular system. A good example is ubiquinone, which is the fully reduced form of Coenzyme Q10.

Ubiquinone helps prevent congestive heart failure, heart attacks, and heart arrhythmias. Ubiquinone is required for the proper function of cardiovascular system, and is found in almost every cell in the body.

The reason why ubiquinone is so ubiquitous is because the mitochondria require ubiquinone to function.

Specifically, CoQ-10 is a component of the electron transport chain used by the mitochondria for aerobic cellular respiration, which generates ATP to fuel the cell.

That means that if the body becomes deficient in ubiquinone, then the mitochondria would stop producing energy. Without energy, cells cease to function and eventually die. I think this explains why statins harm the muscle cells the most. That’s because muscles cells are rich with many mitochondria, and therefore ubiquinone, in order to meet the high energy requirements for muscle contractions.

The Different Types of Cholesterol

There are many different types of cholesterol that the body employs. Two such examples are HDL cholesterol and LDL cholesterol. HDL stands for “High Density Lipoprotein” and LDL stands for “Low Density Lipoproteins”.

Lipoproteins are a complex composition of proteins that transports fat molecules (a.k.a. lipids) throughout the body. They also may carry cholesterol molecules.

HDL Cholesterol

High-Density Lipoproteins (HDL) refer to lipoproteins that don’t carry that many fat molecules. That means HDL molecules have a higher ratio of proteins than fat, resulting in a higher “density” given that proteins weigh more than fats at the same volume. Because HDL molecules don’t carry that many lipids, they tend to be smaller in size.

A reason why HDL molecules do not (initially) have many lipids, is because their function is to remove lipids and cholesterol from different parts of your body back to the liver to be recycled and eliminated.

HDL cholesterol is commonly thought to be “good” cholesterol because this is the type that carries cholesterol from all over your body back to the liver to be recycled and eliminated.

LDL Cholesterol

On the other hand, Low-Density Lipoproteins (LDL) refer to lipoproteins that carry a lot of lipids. That means LDL molecules have a higher ratio of fats than proteins, at least compared to HDL cholesterol. The higher ratio of fats is what makes LDL “low” in density. LDL molecules tend to carry a lot more lipids than HDL, and therefore LDL is comparatively bigger in size than HDL molecules.

Now the reason why LDL molecules carry so many lipids is due to its function. The function of LDL is to distribute lipids and cholesterol to different cells throughout the body.

And it is popularly thought that LDL is the “bad” type of cholesterol. That’s because researchers found that high LDL cholesterol levels correlated with the build up of cholesterol in your arteries.

But it isn’t as clear cut as that. To be honest with you, our body uses LDL molecules to move around cholesterol and lipids to the places that they need to go. Our cells do need lipids. Our cells do require cholesterol.

LDL cholesterol only becomes a problem if they get stuck into the blood vessel endothelium and become oxidized. Atherosclerosis may develop, which is the hardening and internal thickening of arteries- such that there is less space for blood to travel through an artery.

And usually high LDL levels correlate with atherosclerosis and other cardiovascular diseases.

Related Links

Books about Cholesterol & Statins


  1. Cellular control of cholesterol by Peter Takizawa of the Department of Cell Biology [PDF]
  2. What Is Cholesterol? [NHLBI]

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