Published 6th September 2022

What is cholesterol, and what does it do?

Cholesterol — we’ve all heard the name. Most often, it crops up in relation to heart disease. 

While high levels of some forms of cholesterol are linked to heart disease risk, it might surprise some of you to learn that cholesterol is essential for your survival. 

So, we’ll focus on what it is and why you can’t live without it.

Before we start, we should mention that this article isn’t an endorsement to increase your cholesterol intake: Your body can produce all it needs.

What is cholesterol?

Cholesterol is a yellowish, waxy substance. It’s a type of lipid, or fat.

You might be most familiar with dietary cholesterol, which is present in foods such as red meat, milk, egg, and shellfish. However, the vast majority of cholesterol in your body is produced by your body.

All of your cells contain cholesterol. In fact, every cell in every animal contains it. Even plants make it, but in much smaller quantities.

Although cholesterol is produced throughout your body, liver cells create the most.

Once created, cholesterol enters your bloodstream. It travels through your blood vessels in groups called lipoproteins. 

One type is the famous high-density lipoprotein (HDL) cholesterol. This is also called "good” cholesterol. Another is the infamous low-density lipoprotein (LDL), or “bad,” cholesterol.

In simple terms, LDL mostly moves cholesterol from the liver to the rest of the body, while HDL mostly shuttles cholesterol back to the liver. 

When a compound is produced in every cell and transported far and wide in your blood, you know it’s doing something important. So, what’s it up to in there?

Membranes

Each cell is wrapped in a membrane. Among other tasks, the membrane keeps important bits inside the cell and unwanted bits outside it.

Cholesterol is a vital component of these cell membranes.

Membranes are not solid, and their parts are in constant flux. They have to be flexible enough to bend and reshape when needed but sturdy enough not to burst and leak.

Cholesterol does two seemingly opposite jobs. It helps increase the order within the membrane, keeping all the components tightly packed. But at the same time, it makes sure that the membrane stays fluid. 

Membranes also act as gatekeepers. They have channels, or pores, that are specific to different compounds. These pores allow things to enter and leave the cell as required.

Cholesterol has a job to do here, too. It interacts with protein pores, helping guide the traffic into and out of the cell.

A building block

Cholesterol’s benefits extend beyond the cell membrane. It’s also crucial in producing many compounds.

For instance, cholesterol is essential for the production of the “sunshine” vitamin, vitamin D.

A form of cholesterol called 7-dehydrocholesterol is present in the upper layers of your skin. When sunlight hits this compound, it’s converted into vitamin D.

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Vitamin D is involved in a wide range of functions. For instance, it's converted into an active form called calcitriol, which controls how much calcium is absorbed from your gut into your body. 

Calcium is vital for building and maintaining bones and teeth.

So, by extension, cholesterol helps keep your bones and teeth healthy. And much more besides.

Cholesterol also forms the building blocks of steroid hormones. These include progesterone, estrogen, testosterone, cortisol, and many others.

The importance of steroid hormones can’t be overstated; they’re important players in all manner of roles, including: 

  • metabolism

  • inflammation

  • the immune system

  • the development of sexual characteristics

Quick communication

Picture this: It’s late at night, and you’re moving slowly across the room to turn on a light. As your feet move quietly across the carpet, you place your foot on a rogue piece of Lego.

But before the pain has fully registered, your foot is already inches off the ground. You can thank cholesterol for that quick response.

Many of the nerves in your body are coated in a waxy substance called myelin. 

This myelin sheath insulates nerves and helps them conduct their messages more quickly. And, you’ve guessed it, myelin can’t form without cholesterol.

Bile

Bile is another bodily product with a bad name. But bile helps you digest fats and oils by making them soluble

And without bile, fat-soluble vitamins — such as vitamins A, D, and E — can’t be absorbed. 

Bile also helps increase the absorption of nutrients by suspending them in blobs called micelles.

And cholesterol is vital for the synthesis of bile.

Celebrating cholesterol

Although we’ve only covered a handful of cholesterol’s important functions, it’s clearly a key player in the game of life. 

Finally, we should reiterate that eating more high-cholesterol foods won’t benefit your health. Your body can synthesize all the cholesterol you need.

Also, many of the foods that contain cholesterol are high in saturated fats. It’s best to enjoy these foods once in a while.

Sources

Cholesterol and plants. Journal of Chemical Education. (2005). https://pubs.acs.org/doi/pdf/10.1021/ed082p1791 

Cholesterol content in cell membrane maintains surface levels of ErbB2 and confers a therapeutic vulnerability in ErbB2-positive breast cancer. Cell Communication and Signalling. (2019). https://biosignaling.biomedcentral.com/articles/10.1186/s12964-019-0328-4 

Cholesterol, inflammation and innate immunity. Nature Reviews Immunology. (2015). https://www.nature.com/articles/nri3793 

Cholesterol interactions with phospholipids in membranes. Progress in Lipid Research. (2002). https://www.sciencedirect.com/science/article/abs/pii/S0163782701000200 

Cholesterol provides nonsacrificial protection of membrane lipids from chemical damage at air–water interface. PNAS. (2018). https://www.pnas.org/doi/10.1073/pnas.1722323115 

High cholesterol level is essential for myelin membrane growth. Nature Neuroscience. (2005). https://www.nature.com/articles/nn1426 

Indications on the use of vitamin D and vitamin D metabolites in clinical phenotypes. Clinical Cases in Bone and Mineral and Bone Metabolism. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3213838/ 

Kinetics of formation of bile salt micelles from coarse-grained Langevin dynamics simulations. Soft Matter. (2016). https://pubs.rsc.org/en/content/articlehtml/2016/sm/c6sm00763e 

Mechanisms and regulation of cholesterol homeostasis. Nature Reviews. (2019). https://www.nature.com/articles/s41580-019-0190-7 

Physiology, cholesterol. (2022). https://ncbi.nlm.nih.gov/books/NBK470561/ 

Steroid hormones: relevance and measurement in the clinical laboratory. Clinics in Laboratory Medicine. (2013). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3636985/ 

The Continuing Importance of Bile Acids in Liver and Intestinal Disease. JAMA Internal Medicine. (1999). https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/1105662 

Vitamin D. (2022) https://ods.od.nih.gov/factsheets/VitaminD-Consumer/ 

What is blood cholesterol? (2022). https://www.nhlbi.nih.gov/health/blood-cholesterol 

Who, what, where and when — influences on cutaneous vitamin D synthesis. Progress in Biophysics and Molecular Biology. (2006). https://www.sciencedirect.com/science/article/pii/S0079610706000204 

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