Have you ever wondered what the deal is with cholesterol? I mean, society kind of makes it seem like a bad thing. “Watch your cholesterol” and “beware of cholesterol” and “you don’t want to have high cholesterol!” But has anybody wondered why we even need cholesterol in the first place? How the body makes it, absorbs it, and uses it?
Well I wondered! And lucky for me, I’m in a medical school program where I get to choose what I want to learn when I want to learn it. And so I learned about cholesterol.
Just to warn you, this may get a bit “science-y” so if you don’t care much about the science, then feel free to scroll to the bottom where I have a chart showing which foods to avoid, eat sparingly, and eat plentifully if you’re looking to lower your cholesterol intake.
So the first question we need to answer is: why do we even need cholesterol? It turns out that cholesterol is very important for our cells. The structure of cholesterol is perfect for our cell membranes; it allows them to be both appropriately fluid and appropriately rigid. If our cell membranes get too stiff, then it’s difficult for them to move and pick up nutrients. If they get too fluid, then they lose a layer of protection and structural integrity. Having that “perfect” amount of cholesterol around keeps our cells balanced, and keeps us healthy.
We also need cholesterol to help us dispose of excess fats. Fats are hydrophobic or “water fearing” which simply means that when you mix water and oil they just don’t mix very well! Because our bodies are made up of a LOT of water, fats can’t just dissolve the way sugar can (think about how well sugar dissolves in water when you mix them). Instead, fats need another way of moving around the body. It turns out the way that they exit the body is through the help of cholesterol. Through a series of biological changes in the liver, cholesterol eventually becomes a particle called a bile salt, which is amphipathic meaning that the inside is hydrophobic and binds to fats, while the outside is hydrophilic and can interact with water. In this way, the bile salt can help remove excess fats that we don’t need. If we didn’t have cholesterol, we couldn’t make bile, and then we wouldn’t have a way of disposing of fats as waste.
Our bodies can also use cholesterol to make Vitamin D, which is a cofactor to calcium and helps with bone health. We also use it to make steroids like estrogen, testosterone, cortisol, and aldosterone. Cortisol is necessary to provide adequate energy to all of our cells and organs- and without it, we couldn’t live.
So, as it turns out, cholesterol is pretty important! Cholesterol, like fat, is hydrophobic; meaning it can’t just float through your blood. It needs help from other substances to move around. There are two ways it does this; one is through a special package made in your intestines called a chylomicron. The chylomicrons carry large amounts of triglycerides (fancy version of fats) and cholesterol that come from the diet. Another way is to make a similar special package in the liver called VLDL which is similar to a chylomicron except that it packages cholesterol that we make in our bodies while chylomicrons package cholesterol that we get from food. But what good are packages if you don’t have a mailman? This is where a particle called HDL comes in. HDL donates special proteins to the chylomicron and VLDL to “tag” them. Sort of like putting an address on them of where they will get delivered. The appropriate address may be fat cells or other tissues. The tag will allow these tissues to recognize the VLDL and chylomicrons and allow the absorption of fats in order to turn them into energy. The more they donate their contents to tissues, the smaller they become. Eventually they will donate their “tags” back to HDL, and at this point the chylomicron will become a remnant picked up by the liver, and VLDL will become a particle called LDL which is denser and contains more cholesterol relative to fat. Once it becomes LDL, this is another special signal to the body that cells should pick up the particle and use the remaining cholesterol for all the important things I mentioned above.
We commonly consider HDL to be “good cholesterol” and LDL to be “bad cholesterol.” But why? After all, LDL is the one delivering all the cholesterol to our cells to use for good and important things! So what’s the deal?
HDL is special. This is because in the event that you have too much cholesterol, it can actually pick up the extra pieces and store it inside. It’s protective in this way. But LDL can also carry cholesterol! Why is that different? It turns out that LDL has a “tag” on it’s surface that is susceptible to oxidation. When it gets oxidized, the body no longer recognizes it and tries to attack it. (Side note- this is where antioxidants like vitamin E can help prevent the oxidation from occurring). Our immune system attack will collect large amounts of unrecognizable LDL particles, and this can eventually start to adhere to the inner lining of our blood vessels. Over time, these collections can start to impair normal blood flow, and increase our risk for coronary artery disease and heart problems. Additionally, cholesterol is stuck inside unrecognizable LDL particles and can’t get used by our tissues. When the body doesn’t think it has enough cholesterol (as in when cholesterol is hiding), it will start to produce more of it’s own, and cholesterol levels in the blood go up.
Obviously, the movement of fats and cholesterol throughout the body is very intricate and requires lots of special packaging. Because it’s more involved, there are more places along the pathway where things can go wrong. And this is part of the reason high cholesterol is such a huge chronic problem in the United States. A problem in any one of the signals can lead to high cholesterol, and the diet can also play a role.
So what can you do to lower your risk for high cholesterol and corresponding vascular problems? Exercise, don’t smoke, and avoid foods that are high in cholesterol.
Here’s what the National Heart, Lung, and Blood Institute recommends:
And now you know!