What Is Cholesterol?

Medically reviewed by
Charles Whitcomb, MD
, Cardiologist at University of California, Davis, CA  | Written by 
Emily Wagner

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When you hear the word “cholesterol,” you probably think of it in a bad light. Many of us have had our doctors tell us that we need to lower our cholesterol levels, but there’s more to learn about this waxy substance. Our bodies need cholesterol to function properly, but too much can be harmful to our health.1

Learning what the different types of cholesterol are, where it comes from, and the conditions it plays a role in can give you a better understanding of your overall health. If your doctor has you watching your cholesterol levels, this article may be helpful to you.

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What is High Cholesterol?

Types of Cholesterol

Cholesterol tends to be a catch-all term referring to the waxy, fat-like substance in our bodies. Your liver makes all the cholesterol your body needs, with the rest coming from your diet. This substance is important for making new cells, hormones, and vitamin D.2

There are two main types of cholesterol in your body. Since cholesterol is fatty and can’t dissolve in your blood, it’s carried in protein particles known as lipoproteins. Low-density lipoprotein (LDL) transporting cholesterol is often referred to as “bad cholesterol.” On the other hand, high-density lipoprotein (HDL) transporting cholesterol is your “good cholesterol.”3

Your body needs both LDL and HDL to function properly, but it’s important to keep these levels in check. It’s best to have a healthy balance of low LDL levels and high HDL levels.4

LDL vs. HDL

Cholesterol carried by low-density lipoprotein (LDL) is responsible for many cholesterol-related diseases — if your levels are too high, it begins forming deposits in your blood vessels known as plaques. These sticky plaques collect more blood cells and fats, eventually blocking blood flow through the vessel. The higher your LDL cholesterol levels are, the higher your risk of other cardiovascular complications.

On the other hand, cholesterol carried by high-density lipoprotein (HDL cholesterol) collects LDL cholesterol from your bloodstream and brings it to your liver to be excreted from your body. Think of HDL as a garbage truck, traveling around your body to collect the trash bags (LDL). They then bring them to the dump (your liver) to be thrown away. The higher your HDL cholesterol levels are, the lower your risk for cardiovascular complications. The most common cause of low HDL is diabetes or “prediabetes” (metabolic syndrome), both of which increase risk for vascular events.

Triglycerides

Triglycerides are different from cholesterol — they’re a type of fat (lipids) your body creates from extra calories it doesn’t immediately use. These lipids are stored as an energy source in your fat cells, and they’re released in between meals to give you a boost of energy.5

A healthy amount of triglycerides is important for your body’s normal functioning. However, if you eat a high-calorie diet, drink alcohol in excess, or have diabetes or “prediabetes,” your triglycerides may be too high, which increases your risk of cardiovascular complications.

Cholesterol-Related Diseases

Imbalanced or high cholesterol levels increase your risk of heart disease and other cardiovascular conditions. If you have imbalanced cholesterol levels, you may be diagnosed with dyslipidemia. Even if your levels aren’t necessarily high, they can be “dysfunctional” and lead to other complications.

On the other hand, hypercholesterolemia is diagnosed when your cholesterol levels are higher than normal. High LDL levels can cause plaques to form in your blood vessels, preventing blood from flowing through them properly. According to the Cleveland Clinic, hypercholesterolemia is extremely common and affects roughly 1 out of every 20 individuals.6

Complications of Cholesterol-Related Diseases

Plaques from fatty deposits cause your blood vessels to become stiff and narrow. When this occurs in your arteries, you may develop a condition known as atherosclerosis. This limits the amount of oxygen-rich blood flowing from your heart to other areas of your body, including your heart, brain, and extremities.7

When plaque buildup occurs in your heart’s arteries, blood flow is limited, which increases your risk of a heart attack. This is called coronary artery disease (CAD), which is the most common type of heart disease. You may experience chest pain, shortness of breath, and faintness. If left untreated, CAD can eventually lead to heart attack and heart failure.8

Sometimes, plaques break off and form blood clots that flow through your blood vessels to your heart or brain. If a clot becomes stuck in a blood vessel, it blocks blood flow, cutting off oxygen and causing a heart attack. High LDL cholesterol levels increase your risk of heart attack (blood clot in your coronary arteries) or ischemic stroke (blood clot in your carotid arteries, or the blood vessels that deliver blood to your brain and head).

Risk Factors for Cholesterol-Related Diseases

There are certain risk factors that can affect your cholesterol levels, increasing your risk of cholesterol-related diseases. Some of these risk factors you can control, while others you can’t. Your doctor may recommend that you make certain lifestyle changes to address some of these risk factors and lower your cholesterol.

Cholesterol-related disease risk factors include:9

  • Older age: Anyone can develop high cholesterol, but it’s more common in people over the age of 40. This is because your liver becomes less effective at removing LDL as you age.
  • Genetics: Some people have familial hypercholesterolemia, a genetic disorder that causes their bodies to produce too much LDL, regardless of their diet and lifestyle choices.10
  • Poor diet choices: Your body makes all the cholesterol it needs, so eating a diet high in trans fats and saturated fats can raise your cholesterol levels. These are found in highly processed foods, dairy products, and fatty red meats.
  • Smoking: Smoking tobacco can lower your HDL levels.
  • Drinking alcohol: Alcohol has been shown to increase your total cholesterol level.
  • Obesity: Having a high body mass index (BMI) over 30 increases your risk of high cholesterol.
  • Lack of physical activity: Exercise increases your HDL — without enough physical activity, your body has a harder time getting rid of excess “bad cholesterol.”

Checking Your Cholesterol Levels

According to the National Heart, Lung, and Blood Institute (NHLBI), your first cholesterol screening should take place during childhood, typically when you are age 9 to 11. After that, your doctor will want to check your cholesterol levels every five years to make sure they stay within a healthy range.

As you age, you’ll have cholesterol screenings more frequently. For women ages 55 to 65 and men ages 45 to 65, screening should be done every one to two years. Some people with higher levels or underlying health conditions may have more frequent testing. Once you turn 65, you should have annual screenings.11

Cholesterol Screenings and Other Blood Tests

Cholesterol screening is done with a simple blood test known as a lipid panel, which measures your LDL, HDL, triglycerides, and total cholesterol. A lipid panel is often ordered alongside other tests, including:12

  • Complete blood count (CBC): measures levels of red blood cells, white blood cells, and platelets
  • Hemoglobin A1c (HbA1c): measures the average blood sugar level over three months
  • Basic metabolic panel: measures levels of vitamins, electrolytes, and your fasting blood sugar

Your doctor will have you fast for at least 9 to 12 hours before these tests so that no recent food or drink interferes with the readings. A nurse or phlebotomist (a medical professional trained to take blood) will insert a small needle into a vein in your arm and draw two to four small tubes of blood. It may take a couple of hours or up to a few days to get your results back.

The Centers for Disease Control and Prevention (CDC) states that optimal cholesterol levels are:1

  • LDL cholesterol: around 100 milligrams/deciliter of blood (mg/dL)
  • HDL cholesterol: around 50 mg/dL for women and 40 mg/dL for men
  • Triglycerides: less than 150 mg/dL
  • Total cholesterol: around 150 mg/dL

If you have high cholesterol levels, your doctor may recommend a combination of medications and lifestyle changes to help. Watching your diet and getting more physical activity can help lower your levels.