Cholesterol

Cholesterol is a waxy, fat-like substance that is found in all cells of the body, especially cells' outer membranes, and in the bloodstream. The body needs a certain amount of cholesterol to work properly. The majority of cholesterol in the body is made by the body, with only a small amount coming from foods.

Chemical structure of cholesterol. Source: Wikimedia Commons.

Types

Two main kinds of lipoproteins carry cholesterol throughout the body:

• Low-density lipoprotein (LDL) cholesterol is sometimes called bad cholesterol.
• High-density lipoprotein (HDL) cholesterol is sometimes called good cholesterol.
  • HDL carries cholesterol from other parts of the body back to the liver. The liver removes the cholesterol from the body. The higher the HDL cholesterol level, the lower the chances of getting heart disease (Coronary Artery Disease).

Description

Blood is watery, and cholesterol is fatty. Just like oil and water, cholesterol and water don't mix. To travel in the bloodstream, cholesterol is carried in small packages called lipoproteins (HDL and LDL), which are small bubbles containing fat. The small packages have fat (lipid) on the inside and proteins on the surface. The cholesterol dissolves in the fat portion, inside the bubble, while the outer layer consisting of protein is soluble in water and so can float through the blood stream efficiently.

Role of Cholesterol in the Body

All cell membranes cholesterol. Tissues such as the brain, liver, and spinal cord contain particularly high levels of cholesterol.

The body also uses cholesterol to make steroid hormones, such as cortisol and testosterone. Cholesterol is synthesized into vitamin D. Cholesterol and other lipids make up bile, which is used to help digest fatty foods.

How It Works

Most of the cholesterol in the body is made by organs such as the liver. A smaller amount comes from the diet. The body adjusts the amount of cholesterol it makes to compensate for the amount that is obtained from foods.

Foods that are particularly good sources of cholesterol include eggs, meats, and dairy products.^[1]

Cholesterol is excreted in the bile. Most of this cholesterol is reabsorbed into the body as the bile passes through the intestines.

Diseases Involving Cholesterol

• High blood cholesterol (hypercholesterolemia)
• Familial hypercholesterolemia
• Smith-Lemli-Opitz Syndrome, a disease caused by the inability to make cholesterol

Cholesterol testing

The National Heart, Lung, and Blood Institute makes the following recommendations for cholesterol testing: In all adults aged 20 years or older, a fasting lipoprotein profile (total cholesterol, LDL, HDL, and triglyceride) should be obtained once every 5 years. If the testing opportunity is nonfasting, only the values for total cholesterol and HDL cholesterol will be usable. In such a case, if total cholesterol is 200 mg/dL or HDL is <40 mg/dL, a repeat lipoprotein profile is needed for appropriate management based on LDL.^[2]

Drugs that lower cholesterol

Because high cholesterol levels are associated with increased risk of heart disease, significant efforts have been devoted to developing drugs to lower cholesterol levels. One class of these drugs, the statins, work by blocking an enzyme used to make cholesterol. They may also help the body reabsorb cholesterol from atherosclerotic plaques, helping prevent further blockage in the blood vessels. Statins include well-known medications such as atorvastatin (Lipitor), simvastatin (Zocor), lovastatin (Mevacor), pravastatin (Pravachol), rosuvastatin (Crestor) and others. Besides the statins, other types of drugs to lower cholesterol include cholesterol absorption inhibitors such as ezetimibe (Zetia), bile-acid-binding resins such as cholestyramine (Prevalite, Questran), and combination cholesterol absorption inhibitor and statin (ezetimibe-simvastatin, sold as Vytorin).

History

How cholesterol was discovered

Cholesterol was first discovered in bile and gallstones in 1769 by Francois Poulletier de la Salle. It was found in the blood in 1833. In 1924, Gage and Fish showed that blood contained small fatty molecules for several hours after fatty meals. HDL was isolated from horse blood in 1929, and LDL was isolated in 1950.^[3]

The 1964 Nobel Prize in Physiology or Medicine was awarded to Konrad Bloch and Feodor Lynen "for their discoveries concerning the mechanism and regulation of the cholesterol and fatty acid metabolism."^[4] Michael S. Brown and Joseph L. Goldstein shared the 1985 Nobel Prize in Physiology or Medicine "for their discoveries concerning the regulation of cholesterol metabolism."^[5]

How cholesterol was named

The name originates from the Greek chole (bile) and stereos (solid), and the chemical suffix ol for an alcohol. The term has been in use since 1894.^[6]

Research

Both high and low cholesterol levels have been found to be associated with worse outcomes in certain diseases. In 1961, analysis of data collected in the Framingham Heart Study revealed that high cholesterol, along with high blood pressure, was associated with an increased risk of heart disease. High HDL cholesterol levels were shown in 1988 to protect against death.^[7] Another large study showed that patients with heart failure who had low cholesterol were significantly more likely to die.^[8]

References

1. ↑ USDA. Nutrition and Your Health: Dietary Guidelines for Americans. Table E-18. Dietary Sources of Cholesterol Listed in Decreasing Order.
2. ↑ National Cholesterol Education Program, National Heart, Lung, and Blood Institute, National Institutes of Health. Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). NIH Publication No. 01-3670, May 2001. PDF
3. ↑ Olson RE. Discovery of the lipoproteins, their role in fat transport and their significance as risk factors. J Nutr. 1998 Feb;128(2 Suppl):439S-443S. Abstract | Full Text
4. ↑ Nobel Prize Foundation Web site. The Nobel Prize in Physiology or Medicine 1964.
5. ↑ Nobel Prize Foundation Web site. The Nobel Prize in Physiology or Medicine 1985.
6. ↑ Merriam-Webster Online. Cholesterol.
7. ↑ National Heart, Lung, and Blood Institute Web site. Framingham Heart Study: Research Milestones.
8. ↑ Horwich TB, Hamilton MA, Maclellan WR, Fonarow GC. Low serum total cholesterol is associated with marked increase in mortality in advanced heart failure. J Card Fail. 2002 Aug;8(4): 216-224. Abstract

External Links

• American Heart Association
• Cholesterol (wikipedia)

Related Accredited Articles

1. Ask the Doctor Q&A: Menopause and Cholesterol
2. Content from Harvard Medical School