What is Cholesterol?

You asked: What is Cholesterol?

To get into what cholesterol is and why it even exists other than to contribute toward heart disease, it’s important to know where it comes from, what else it does, and to understand the balance of its good and bad forms.

Cholesterol is a compound that our bodies use to make various hormones and components that help digest food called bile acids. In fact, it’s such an important part of how our body works that the liver makes upwards of 80% of it from scratch using carbohydrates and protein! The other 20% is taken is from fats in our diet that our intestines break down only to reassemble once absorbed. This is why despite many people attempting to lower their cholesterol with diet changes alone, it’s often not enough to do that alone.

If you think about cholesterol as a form of fat that needs to get to various parts of the body in order to be turned into useful things such as hormones, it needs to be transported in the bloodstream. If you’ve ever put oil into water, you know that it won’t dissolve. In order to do this effectively, the liver puts cholesterol and other fat, called triglycerides, into various particles and coats them with proteins, called apolipoproteins, which make the particles they create soluble. Now we’ll let you in on a secret… when we hear about good cholesterol and bad cholesterol, we’re actually talking about the different apolipoproteins and the particles they make. The cholesterol and fats inside of the particles are actually identical, although in different proportions depending on the particle.

What are the kinds of cholesterol?

It’s easy to think about the various types of cholesterol particles once you realize that they are named based on their ratio of fat to protein. The less protein and the more fat they have, the lower the density of the particle. Each particle has specific apolipoproteins associated with them, which also make them easy to differentiate.

Blausen_0227_Cholesterol

LDL – Commonly known as “the bad cholesterol,” low density lipoprotein (LDL) contains a high proportion of fat compared to protein. The apolipoprotein on these particles is called ApoB-

100. ApoB-100 is how LDL receptors in the body recognize this particle and allow those cells that need cholesterol to absorb this particle from the bloodstream and use its contents to make whatever fun hormone or other product it needs to. However, once the cells that use cholesterol to make things have enough, they stop producing the LDL receptor. This means that they stop absorbing LDL particles from the bloodstream and they’re left to continue circulating. This is why LDL gets its bad reputation. With more LDL circulating in the bloodstream, it gets eaten up by cells calls macrophages, which you can think of as the clean-up crew. However, the macrophages can’t actually get rid of the cholesterol they take in so they end up depositing into the walls of arteries and causing inflammation. This is how blockages – also known as plaques – form in blood vessels over time.

HDL – Commonly known as “the good cholesterol,” high density lipoprotein (HDL) has a high protein content compared to fat and is marked by the apolipoprotein called ApoA-1. HDL is known as the type of cholesterol that is protective against heart disease because it functions to actually pick up extra cholesterol from the body and bring it back to the liver to be re-processed instead of being deposited into arteries and forming plaques.

VLDL – You can think of very low density lipoprotein (VLDL) particles as being like LDL particles, but with even more fat in them. As they drop off deliveries of fat throughout the body, they become intermediate density lipoproteins (IDL) and can either be reabsorbed by the liver for re-processing or continue delivering fat to the body and ultimate become LDL.

Chylomicrons – These particles are made by the intestines as we absorb fat along with bile acids, the product of cholesterol that helps absorb fat from food. Chylomicrons are brought to the liver where the fat from your food can then be processed into more cholesterol particles.

What will you see on your cholesterol blood tests?

CholesterolThe typical test for cholesterol, known as a lipid panel, will give measurements of total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. For many people, these numbers are enough to assess your risk of heart disease if you know what you’re looking at.

Total Cholesterol is the total amount of cholesterol in your blood. It’s helpful as a general overlook, but it has some caveats. For example, someone with a high total cholesterol that’s because of a high HDL cholesterol with a low LDL cholesterol might actually have a lower risk of heart disease than someone with a normal total cholesterol number and average levels of LDL and HDL cholesterol.

Triglycerides refer to the total amount of fat content circulating and is helpful in thinking about heart disease risk, although less so than the cholesterol levels. Triglycerides can fluctuate a little more than the other levels depending on what you eat.

What about particle size, number, and Lp(a)?

In addition to the typical numbers you’ll see on your cholesterol tests, there has been a lot of talk about how we can do better to assess risk of heart disease. It turns out that there are some other methods, often referred to as advanced lipid testing. There are 3 other tests that have shown some promise in further risk stratifying cholesterol in heart disease prevention.

It turns out that in addition to the total amount of LDL cholesterol you have circulating, the size of the particles matters. While this often relates to the number of particles, they aren’t exactly the same measurement. For example, if you were filling a cup with snacks, you could fit a lot more peanuts than Brazil nuts in the same size cup. There is some evidence that have a higher number as well as smaller size of LDL particles contributes toward a higher risk for heart disease than a lower number of larger LDL particles. Since ApoB-100 is the apolipoprotein specific for LDL, advanced lipid testing can also include a test for ApoB-100 to see the number of particles you have.

Lp(a) (AKA “L” “P” “little ‘a’” or lipoprotein little ‘a’) is yet another lipoprotein that has come into the spotlight more recently. Studies have shown that high Lp(a) levels are present in about 19% of people with heart disease at ages younger than expected – called premature coronary heart disease – and more importantly, that of those with premature heart disease and high Lp(a) levels, about 13% of them had normal lipid panel testing. Even more importantly, all the lifestyle changes that people recommend to improve cholesterol levels aren’t as effective in changing Lp(a) levels. For that reason, Lp(a) testing is becoming more common for those with a strong family history and other non-lifestyle risk factors for heart disease.

What can you do about it?

Well, you can’t change what your parents gave you (i.e. genetics), but you can do a lot of other things to improve your cholesterol profile. The first step is knowing what you’re working with. Go get your cholesterol checked and talk with your doctor about any need for advanced testing. Lifestyle changes you can make to improve cholesterol mainly fall into diet and exercise.

Since now you know that only about 20% of your cholesterol comes from fats you eat, it’s good to know what kinds of dietary changes can help your body decrease the 80% that it makes from scratch. Lowering the amount of carbohydrates and processed sugars will really help you lower the amount of cholesterol your body makes, in addition to reducing your fat intake. Increasing the fiber in your diet can also help.

The recommended exercise is at least 30 minutes per day of moderately intense exercise on most days of the week. This means at least 150 minutes of exercise to the point where you’re out of breath enough to not be able to finish more than a few words of a sentence. Talk to your doctor about an exercise program before you start though, especially if you have any symptoms of anything and if you know you have risk factors for heart disease.

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Published by: Mark P. Abrams, MD

I'm an Internist, Educator, and Cardiology fellow in training. As the Director of Patient Engagement at Heartbeat Health, my goal is to make trustworthy information easily accessible and more available so that people can become more active members of their healthcare teams. By joining together, we can work toward keeping more people healthier, happier, and living longer fulfilling lives.

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