Merck Manual

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Overview of Cholesterol and Lipid Disorders


Michael H. Davidson

, MD, FACC, FNLA, University of Chicago Medicine, Pritzker School of Medicine;

Pallavi Pradeep

, MD, University of Chicago

Reviewed/Revised Jul 2023
Topic Resources

The body needs fats (lipids) for growth and energy. It also uses them to synthesize hormones and other substances needed for the body’s activities. The body may deposit excess fat in blood vessels and within organs, where it can block blood flow and damage organs, often causing serious disorders.

Important lipids found in the blood are

  • Cholesterol

  • Triglycerides

Cholesterol is an essential component of cell membranes, of brain and nerve cells, and of bile, which helps the body absorb fats and fat-soluble vitamins. The body uses cholesterol to make vitamin D and various hormones, such as estrogen, testosterone, and cortisol. The body can produce all the cholesterol that it needs, but it also obtains cholesterol from food.

Triglycerides, which are contained in fat cells, can be broken down, then used to provide energy for the body’s metabolic processes, including growth. Triglycerides are produced in the intestine and liver from smaller fats called fatty acids Fats . Some types of fatty acids are made by the body, but others must be obtained from food.

Fats, such as cholesterol and triglycerides, cannot circulate freely in the blood, because blood is mostly water. To be able to circulate in blood, cholesterol and triglycerides are packaged with proteins and other substances to form particles called lipoproteins.

There are different types of lipoproteins. Each type has a different purpose and is broken down and excreted in a slightly different way. Lipoproteins include

  • Chylomicrons

  • High-density lipoproteins (HDL)

  • Low-density lipoproteins (LDL)

  • Very low density lipoproteins (VLDL)

Cholesterol transported by LDL is called LDL cholesterol (LDL-C), and cholesterol transported by HDL is called HDL cholesterol (HDL-C).

The body can regulate lipoprotein levels (and therefore lipid levels) by increasing or decreasing the production rate of lipoproteins. The body can also regulate how quickly lipoproteins enter and are removed from the bloodstream.

Levels of cholesterol and triglycerides vary considerably from day to day, due to many factors like stress, dietary habits, exercise, lifestyle, changes in metabolism. From one measurement to the next, cholesterol levels can vary by about 10%, and triglyceride levels can vary by up to 25%.

Lipid levels may be

Lipid levels may become abnormal because of changes that occur with aging, various disorders (including inherited ones), use of certain medications, or lifestyle (such as consuming a diet high in saturated fat, being physically inactive, or being overweight).


Complications of abnormal lipid levels

The effect of triglyceride levels on the risk of heart attack is less clear-cut. But very high levels of triglycerides (higher than 500 milligrams per deciliter of blood, or mg/dL [5.65 mmol/L) can increase the risk of pancreatitis Overview of Pancreatitis Pancreatitis is inflammation of the pancreas. The pancreas is a leaf-shaped organ about 5 inches (about 13 centimeters) long. It is surrounded by the lower edge of the stomach and the first... read more .

Measuring lipid levels

The fasting lipid profile (sometimes called a lipid panel) is the levels of total cholesterol, triglycerides, LDL cholesterol, and HDL cholesterol measured after a person fasts for 12 hours. Doctors usually do this test every 5 years starting at age 20 as part of assessing whether the person is at risk of coronary artery disease Overview of Coronary Artery Disease (CAD) Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more Overview of Coronary Artery Disease (CAD) .

In children and adolescents, screening with a fasting lipid profile is recommended between the ages of 2 and 8 years if the child has risk factors, such as a family member with severe dyslipidemia Dyslipidemia Dyslipidemia is a high level of cholesterol and/or triglycerides or a low level of high-density lipoprotein (HDL) cholesterol. Lifestyle, genetics, disorders (such as low thyroid hormone levels... read more Dyslipidemia or one who developed coronary artery disease at a young age. In children with no risk factors, screening with a non-fasting lipid profile is usually done once before the child reaches puberty (usually between age 9 to 11) and once more between the ages of 17 to 21.

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