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Cholesterol is a waxy, fat-like substance that's found in all the cells in your body. Your body needs some cholesterol to make hormones, vitamin D, and substances that help you digest foods. Your body makes all the cholesterol it needs. Cholesterol is also found in foods from animal sources, such as egg yolks, meat, and cheese.

If you have too much cholesterol in your blood, it can combine with other substances in the blood to form plaque. Plaque sticks to the walls of your arteries. This buildup of plaque is known as atherosclerosis. It can lead to coronary artery disease, where your coronary arteries become narrow or even blocked.

HDL, LDL, and VLDL are lipoproteins. They are a combination of fat (lipid) and protein. The lipids need to be attached to the proteins so they can move through the blood. Different types of lipoproteins have different purposes:

• HDL stands for high-density lipoprotein. It is sometimes called "good" cholesterol because it carries cholesterol from other parts of your body back to your liver. Your liver then removes the cholesterol from your body.
• LDL stands for low-density lipoprotein. It is sometimes called "bad" cholesterol because a high LDL level leads to the buildup of plaque in your arteries.
• VLDL stands for very low-density lipoprotein. Some people also call VLDL a "bad" cholesterol because it too contributes to the buildup of plaque in your arteries. But VLDL and LDL are different; VLDL mainly carries triglycerides and LDL mainly carries cholesterol.

The most common cause of high cholesterol is an unhealthy lifestyle. This can include:

• Unhealthy eating habits, such as eating lots of bad fats. One type, saturated fat, is found in some meats, dairy products, chocolate, baked goods, and deep-fried and processed foods. Another type, trans fat, is in some fried and processed foods. Eating these fats can raise your LDL (bad) cholesterol.
• Lack of physical activity, with lots of sitting and little exercise. This lowers your HDL (good) cholesterol.
• Smoking, which lowers HDL cholesterol, especially in women. It also raises your LDL cholesterol.

Genetics may also cause people to have high cholesterol. For example, familial hypercholesterolemia (FH) is an inherited form of high cholesterol. Other medical conditions and certain medicines may also cause high cholesterol.

A variety of things can raise your risk for high cholesterol:

• Age. Your cholesterol levels tend to rise as you get older. Even though it is less common, younger people, including children and teens, can also have high cholesterol.
• Heredity. High blood cholesterol can run in families.
• Weight. Being overweight or having obesity raises your cholesterol level.
• Race. Certain races may have an increased risk of high cholesterol. For example, African Americans typically have higher HDL and LDL cholesterol levels than whites.

If you have large deposits of plaque in your arteries, an area of plaque can rupture (break open). This can cause a blood clot to form on the surface of the plaque. If the clot becomes large enough, it can mostly or completely block blood flow in a coronary artery.

If the flow of oxygen-rich blood to your heart muscle is reduced or blocked, it can cause angina (chest pain) or a heart attack.

Plaque also can build up in other arteries in your body, including the arteries that bring oxygen-rich blood to your brain and limbs. This can lead to problems such as carotid artery disease, stroke, and peripheral arterial disease.

There are usually no signs or symptoms that you have high cholesterol. There is a blood test to measure your cholesterol level. When and how often you should get this test depends on your age, risk factors, and family history. The general recommendations are:

For people who are age 19 or younger::

• The first test should be between ages 9 to 11
• Children should have the test again every 5 years
• Some children may have this test starting at age 2 if there is a family history of high blood cholesterol, heart attack, or stroke

For people who are age 20 or older::

• Younger adults should have the test every 5 years
• Men ages 45 to 65 and women ages 55 to 65 should have it every 1 to 2 years

You can lower your cholesterol through heart-healthy lifestyle changes. They include a heart-healthy eating plan, weight management, and regular physical activity.

If the lifestyle changes alone do not lower your cholesterol enough, you may also need to take medicines. There are several types of cholesterol-lowering drugs available, including statins. If you take medicines to lower your cholesterol, you still should continue with the lifestyle changes.

Some people with familial hypercholesterolemia (FH) may receive a treatment called lipoprotein apheresis. This treatment uses a filtering machine to remove LDL cholesterol from the blood. Then the machine returns the rest of the blood back to the person.

NIH: National Heart, Lung, and Blood Institute

If you have diabetes, your blood glucose, or blood sugar, levels are too high. Glucose comes from the foods you eat. A hormone called insulin helps the glucose get into your cells to give them energy. With type 1 diabetes, your body does not make insulin. With type 2 diabetes, your body does not make or use insulin well. Without enough insulin, the glucose stays in your blood.

Over time, having too much glucose in your blood can cause complications, including:

• Eye disease, due to changes in fluid levels, swelling in the tissues, and damage to the blood vessels in the eyes
• Foot problems, caused by damage to the nerves and reduced blood flow to your feet
• Gum disease and other dental problems, because a high amount of blood sugar in your saliva helps harmful bacteria grow in your mouth. The bacteria combine with food to form a soft, sticky film called plaque. Plaque also comes from eating foods that contain sugars or starches. Some types of plaque cause gum disease and bad breath. Other types cause tooth decay and cavities.
• Heart disease and stroke, caused by damage to your blood vessels and the nerves that control your heart and blood vessels
• Kidney disease, due to damage to the blood vessels in your kidneys. Many people with diabetes develop high blood pressure. That can also damage your kidneys.
• Nerve problems (diabetic neuropathy), caused by damage to the nerves and the small blood vessels that nourish your nerves with oxygen and nutrients
• Sexual and bladder problems, caused by damage to the nerves and reduced blood flow in the genitals and bladder
• Skin conditions, some of which are caused by changes in the small blood vessels and reduced circulation. People with diabetes are also more likely to have infections, including skin infections.

If you have diabetes, you need to watch out for blood sugar levels that are very high (hyperglycemia) or very low (hypoglycemia). These can happen quickly and can become dangerous. Some of the causes include having another illness or infection and certain medicines. They can also happen if you don't get the right amount of diabetes medicines. To try to prevent these problems, make sure to take your diabetes medicines correctly, follow your diabetic diet, and check your blood sugar regularly.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases

Your eyelids help protect your eyes. When you blink, your eyelids spread moisture over your eyes. Blinking also helps move dirt or other particles off the surface of the eye. You close your eyelids when you see something coming toward your eyes. This can help protect against injuries.

Like most other parts of your body, your eyelids can get infected, inflamed, or even develop cancer. There are also specific eyelid problems, including:

• Eyelids that turn in or out
• Eyelids that droop
• Abnormal blinking or twitching

Treatment of eyelid problems depends on the cause.

Metabolism is the process your body uses to make energy from the food you eat. Food is made up of proteins, carbohydrates, and fats. Chemicals in your digestive system (enzymes) break the food parts down into sugars and acids, your body's fuel. Your body can use this fuel right away, or it can store the energy in your body tissues. If you have a metabolic disorder, something goes wrong with this process.

Lipid metabolism disorders, such as Gaucher disease and Tay-Sachs disease, involve lipids. Lipids are fats or fat-like substances. They include oils, fatty acids, waxes, and cholesterol. If you have one of these disorders, you may not have enough enzymes to break down lipids. Or the enzymes may not work properly and your body can't convert the fats into energy. They cause a harmful amount of lipids to build up in your body. Over time, that can damage your cells and tissues, especially in the brain, peripheral nervous system, liver, spleen, and bone marrow. Many of these disorders can be very serious, or sometimes even fatal.

These disorders are inherited. Newborn babies get screened for some of them, using blood tests. If there is a family history of one of these disorders, parents can get genetic testing to see whether they carry the gene. Other genetic tests can tell whether the fetus has the disorder or carries the gene for the disorder.

Enzyme replacement therapies can help with a few of these disorders. For others, there is no treatment. Medicines, blood transfusions, and other procedures may help with complications.