In this article I will discuss the basics about cholesterol and the other cholesterol. We will make the distinction between the molecule cholesterol and cholesterol in the sense that most people know it, what traits of cholesterol are most relevant for maintaining optimal health and how you affect your cholesterol. This article will be part 1 of a two-part series, the second part going into more depth about atherosclerosis and how lipoproteins play a role in cardiovascular disease.
The information in this article comes mainly from this interview by Rhonda Patrick, PhD, with Dr. Ronald Krauss, MD. Dr. Krauss discusses his experience with research into cholesterol, lipoproteins, nutrition and cardiovascular disease. This is a conversation between professional and very in-depth as such. Here, I have summarized the essential message into figures and a brief description.
What is cholesterol?
The term cholesterol can mean 1 of 2 things: 1) the molecule cholesterol or 2) the carriers of cholesterol in the blood, lipoproteins. The make a clear distinction, I will use ‘cholesterol’ to refer to the molecule and ‘lipoproteins’ to refer to HDL, LDL and such.
Cholesterol as a molecule is a fat-soluble compound that the body can manufacture or absorb from food. Cholesterol is the raw material many hormones are made from and is a structural component of cell membranes and neurons.
Cholesterol is commonly used to refer to HDL or LDL, the cholesterol-carrying structures found in the blood. Using medical jargon, HDL and LDL are categorized as lipoproteins = fat proteins.
Lipoproteins can be subdivided into many categories and subcategories. More on that later.
Function Of Cholesterol
I already mentioned that the body can make cholesterol and this will happen especially when little cholesterol is gained through nutrition. Keep in mind: Cholesterol is an essential resource in the body!
Cholesterol is needed to maintain healthy cell membranes in all cells, but it’s especially important for the production of myelin. Myelin is the isolation material that protects neurons and improves their function. The largest quantity of cholesterol can be found in the brain for this very reason.
Cholesterol is also the base from which many hormones are made, such as sex hormones (testosteron, estrogen), cortisol (a stress hormone), aldosteron (involved with blood pressure) and vitamin D (for calcium balance, a.o.).
Finally, cholesterol is crucial for the digestion and absorption of fats. Cholesterol is made into bile salts or is added to bile as-is. Bile acids and bile cholesterol aid suspending fats in digestive juices (see this post about fat digestion for more information).
Luckily for us, the body can make it’s own cholesterol to provide for all the needs, but it is much easier to get some cholesterol from food or to recycle cholesterol from the excreted bile. On top of that, Dr. Krauss remarked that the intake of cholesterol through food has a negligible effect on total cholesterol in blood (remember: cholesterol molecules, not LDL/HDL). Should cholesterol intake exceed the needs of the body, cholesterol (re-)uptake is simply lowered or the output through bile is increased. So no need to worry about having an egg or two for breakfast once in a while ;-).
Lipoproteins: What Are They
The literal translation of lipoprotein means fatprotein, which also covers the structure these particles are made off. Lipoproteins are droplets of fat and fat-soluble compounds, like cholesterol, held together by a coating of large proteins. The protein coating makes the fats water-soluble and transportable by blood.
There are many type of lipoproteins, differentiated by protein coating, the fat droplet composition, but also density and size. The most well-known characterization is based on density:
- VLDL: Very Low Density Lipoprotein – contain a relatively high amount of fats (triglycerides).
- IDL: Intermediate Density Lipoprotein – contain fewer fats and more cholesterol than VLDL.
- LDL: Low Density Lipoprotein – contain the highest proportion of cholesterol relative to triglycerides compared to VLDL and IDL.
- HDL: High Density Lipoprotein – have the highest density of all lipoproteins, but contains the least amount of fats and cholesterol relatively speaking.
- Chylomicron: A lipoprotein made by the gastrointestinal tract cells from newly-absorbed fats from food.
VLDL en HDL worden gemaakt door de lever. VLDL verandert van IDL naar LDL gedurende zijn reis door het lichaam, waarbij steeds meer vet wordt afgegeven en er dus relatief veel cholesterol overblijft. LDL wordt uiteindelijk weer opgenomen door de lever en gerecycled.
VLDL and HDL are made by the liver. VLDL transforms from IDL into LDL during its journey through the body, during which the lipoprotein loses more and more triglycerides and becomes enriched in cholesterol as a result. LDL eventually returns to the liver to be recycled.
Function of lipoproteins
By far the most important function of lipoproteins is triglyceride (fat) transport to all tissues in the body. Chylomicrons transport fats newly absorbed from food to tissues and the liver. The liver repackages triglycerides into VLDLs. VLDLs provide triglycerides to other tissues, transforming the VLDL into IDL and LDL.
Along with fats, lipoproteins also carry fat-soluble nutrients such as vitamins, cholesterol and phospholipids (cell membrane fats). Keep in mind that while lipoproteins do transport cholesterol, this is not their primary function.
The liver also produces HDL particles, whose most important function is to transport excess cholesterol from tissues to the liver. HDL will take cholesterol straight from the tissues to the liver or transfers its cholesterol load to VLDL, IDL or LDL particles for liver recycling. HDL also carries fat-soluble vitamins.
To briefly summarize, these are the take-home messages:
- Cholesterol is een belangrijke bouwstof in het lichaam en de hoeveelheid cholesterol in het lichaam is nauwelijks afhankelijk van hoeveel cholesterol je eet.
- De lipoproteïnes VLDL, IDL, LDL en chylomicrons vervoeren vetten naar weefsels.
- Het lipoproteïne HDL vervoert overmatig cholesterol vanuit het lichaam af naar de lever voor recycling.
- Levergemaakte lipoproteïnes vervoeren ook en cholesterol en vetoplosbare vitamines.
- Cholesterol is an important resource in the body and the amount of cholesterol in your body is not really influenced by how much cholesterol you eat.
- The lipoproteins VLDL, IDL, LDL and chylomicrons transport fats to tissues.
- The lipoprotein HDL transports excess cholesterol from your tissues to the liver for recycling.
- Lipoproteins also transport cholesterol and fat-soluble vitamins.
And with this you now know how cholesterol and ‘cholesterol’ work in your body and why you need them. You might think: “Nicely done, Dagmar, but you haven’t answered my real question yet. Because I want to know how cholesterol affects cardiovascular diseases. That is the reason people get sick from eating cholesterol and saturated fats, right!?”
This question is not easy to answer. Dr. Krauss, who has devoted his carrier to working on cholesterol and lipoprotein research, made this point quite clearly in the interview. Because the answer is quite complex, I will discuss it in the next blogpost: BB009 – Cholesterol and cardiovascular disease.