Cholesterol is a waxy substance found in your blood and in your cells. Your liver makes most of the cholesterol in your body. The rest comes from foods you eat. Cholesterol travels in your blood bundled up in packets called lipoproteins.

Cholesterol comes in two forms:

Low-density lipoprotein (LDL) is the “bad,” unhealthy kind of cholesterol. LDL cholesterol can build up in your arteries and form fatty, waxy deposits called plaques.

High-density lipoprotein (HDL) is the “good,” healthy kind of cholesterol. It transports excess cholesterol out of your arteries to your liver, which removes it from your body.

Cholesterol itself isn’t bad. Your body needs some cholesterol to make hormones, vitamin D, and digestive fluids. Cholesterol also helps your organs function properly.

Yet having too much LDL cholesterol can be a problem. High LDL cholesterol over time can damage your arteries, contribute to heart disease, and increase your risk for a stroke. Getting your cholesterol checked at regular doctor visits and lowering your heart disease risk with diet, exercise, lifestyle changes, and medication can help decrease complications associated with heart disease and improve quality of life.

Cardiovascular and circulatory systems

When you have too much LDL cholesterol in your body it can build up in your arteries, clogging them and making them less flexible. Hardening of the arteries is called atherosclerosis. Blood doesn’t flow as well through stiff arteries, so your heart has to work harder to push blood through them. Over time, as plaque builds up in your arteries, you can develop heart disease.

Plaque buildup in coronary arteries can disrupt the flow of oxygen-rich blood to your heart muscle. This may cause chest pain called angina. Angina isn’t a heart attack, but it is a temporary disruption of blood flow. It’s a warning that you’re at risk for a heart attack. A piece of plaque can eventually break off and form a clot or the artery may continue to become narrowed which can fully block blood flow to your heart, leading to a heart attack. If this process occurs in the arteries going to the brain or within the brain it can lead to a stroke.

Plaque can also block the flow of blood to arteries that supply blood to your intestinal tract, legs, and feet. This is called peripheral arterial disease (PAD).

Endocrine system

Your body’s hormone-producing glands use cholesterol to make hormones such as estrogen, testosterone, and cortisol. Hormones can also have an effect on your body’s cholesterol levels. Research has shown that as estrogen levels rise during a woman’s menstrual cycle, HDL cholesterol levels also go up, and LDL cholesterol levels decline. This may be one reason why a woman’s risk for heart disease increases after menopause, when estrogen levels drop.

Lowered production of thyroid hormone (hypothyroidism) leads to an increase in total and LDL cholesterol. Excess thyroid hormone (hyperthyroidism) has the opposite effect. Androgen deprivation therapy, which reduces levels of male hormones to stop prostate cancer growth, can raise LDL cholesterol levels. A deficiency of growth hormone can also raise LDL cholesterol levels.

Nervous system

Cholesterol is an essential component of the human brain. In fact, the brain contains about 25 percent of the body’s entire supply of cholesterol. This fat is essential for the development and protection of nerve cells, which enable the brain to communicate with the rest of the body.

While you need some cholesterol for your brain to function optimally, too much of it can be damaging. Excess cholesterol in the arteries can lead to strokes — a disruption in blood flow that can damage parts of the brain, leading to loss of memory, movement, difficulty with swallowing and speech and other functions.

High blood cholesterol on its own has also been implicated in the loss of memory and mental function. Having high blood cholesterol may accelerate the formation of beta-amyloid plaques, the sticky protein deposits that damage the brain in people with Alzheimer’s disease.

Digestive system

In the digestive system, cholesterol is essential for the production of bile — a substance that helps your body break down foods and absorb nutrients in your intestines. But if you have too much cholesterol in your bile, the excess forms into crystals and then hard stones in your gallbladder. Gallstones can be very painful.

Keeping an eye on your cholesterol level with recommended blood tests and lowering your risk for heart disease will help improve your overall quality of life.