What Does Cholesterol Actually Do?

Chances are, you've heard a lot about cholesterol — and most of what you've heard has probably been negative. But cholesterol isn't all bad. In fact, everyone needs it to survive.

"Cholesterol is so basic to our survival that we actually make this stuff," says Peter Mercurio, MD, a cardiologist with Northern Westchester Hospital in Mount Kisco, New York.

Read more: What's the Difference Between Triglycerides and Cholesterol?

"Cholesterol is fat the body makes," Dr. Mercurio explains. "Cholesterol is used to make cell membranes," the outer surface of your body's cells.

The human body is made up of trillions of cells, according to the U.S. National Library of Medicine's Genetics Home Reference. And since cholesterol makes up cell membranes, that means cholesterol is in every cell in the body, Harvard Health Publishing notes.

You also need cholesterol to make vitamin D and hormones like estrogen and testosterone, says Harvard Health. Most of the cholesterol your body needs comes from your liver, which manufactures about 80 percent of the cholesterol your body needs for these functions, it adds. The rest comes from foods.

There are a variety of cholesterol types. None are purely fat. Fat alone wouldn't be able to travel through the bloodstream. Cholesterol — also known as a lipid — attaches to a protein. The combination is called a lipoprotein (lipid plus protein), Harvard Health Publishing explains.

The two types most often mentioned are LDL and HDL, short for low-density and high-density lipoprotein. LDL — the bad type — does play a role in building cell membranes, but too much of this type of cholesterol is linked to heart blood vessel disease. HDL — known as the good cholesterol — helps rid the body of excess LDL.

"LDL cholesterol is the type of cholesterol that tends to build up and create problems," Dr. Mercurio says. "HDL helps to transport the leftover LDL away."

It's only when you have too much of the "bad" cholesterol — LDL — that cholesterol becomes a problem. When there's excess LDL, it starts to collect on your blood vessel walls, which eventually narrows your blood vessels, explains the American Heart Association (AHA).

In addition, too much LDL or too little HDL can be unhealthy, according to the AHA. The wrong amount of either type allows cholesterol to build up on blood vessel walls. Those blood vessels carry oxygenated blood to nourish your brain and heart. If they get too narrow, your blood flow is slowed or might even be stopped, potentially causing a heart attack or stroke.

If you have other health concerns, your chances of having a heart attack or stroke due to high cholesterol could be even higher. These concerns include smoking, having high blood pressure or having diabetes, notes the AHA.

Because some cholesterol is good, how do you know if your cholesterol levels are in balance? That's where periodic testing comes into play.

Cholesterol tests are often done as part of an annual physical. If you don't already know, ask your doctor what your cholesterol levels are. LDL should generally be 100 milligrams per deciliter or lower, the National Heart, Lung, and Blood Institute (NHLBI) recommends.

For HDL, men should aim for 40 milligrams per deciliter or higher. For women, HDL should be 50 or higher, according to the NHLBI.

Dr. Mercurio says that HDL is not easy to change, but one thing that can boost HDL is exercise. Exercise can help lower LDL cholesterol too. A healthy diet is also good for reducing LDL, so "eat more plant-based foods and less meat," he advises.

Read more: Foods Not to Eat If You Have High Cholesterol

If a healthier lifestyle doesn't knock down your cholesterol numbers, medications may help. The most commonly prescribed are called statins. These medications reduce the amount of cholesterol the liver makes, according to the NHLBI.