If you are an American adult age 20 or above, chances are you've had your cholesterol levels checked. As infamous as cholesterol's connection to heart disease may be, your body simply cannot do without this soft, waxy substance. It not only plays a structural role in all cells, but also acts as a precursor to the production of compounds your body needs to remain healthy. However, balance is key because excess blood cholesterol can be harmful.
Description
Cholesterol is a lipid, or fat, belonging to a family of compounds called steroid alcohols, or sterols. Its landmark feature, the steroid nucleus, consists of four fused carbon rings named A, B, C and D. Attached to this steroid nucleus are an eight-carbon chain, an alcohol group and a carbon double bond in one of the rings. Cholesterol's chemical structure makes it very hydrophobic, or unable to function in water. According to the Merck Manual, your body can produce all the cholesterol it needs. However, you're likely to get some dietary cholesterol, particularly if your diet includes foods of animal origin.
Cell Membrane Composition
Along with another type of fats called phospholipids, cholesterol is a component in all cell membranes. However, scientists Pamela Champe and Richard Harvey indicate that, unlike phospholipids, which form the actual membrane bilayer, cholesterol mainly helps modulate membrane fluidity. Fluidity is necessary if your cells are to grow and maintain their ability to respond to changes in their environment. To keep the membrane fluid at temperatures conducive to life, your cells often change the fatty acid content of their phospholipids. Cholesterol helps keep cell membranes from becoming too liquid at body temperature.
Hormone Production
Cholesterol is the parent compound from which your body derives all steroid hormones, which are fat-soluble compounds that play crucial roles in your body. Glucocorticoids are examples of steroid hormones that mainly affect your metabolism, decrease inflammation and increase resistance to stress. Mineralocorticoids, on the other hand, maintain salt and water balance. Estrogens and androgens primarily affect the development and function of female and male secondary sex organs, respectively, while progestins help regulate menstrual cycles and maintain pregnancy. The Switzerland-based University Institute of Psychiatry also reports the recent discovery of "neurosteroids," which your brain can directly produce from cholesterol.
Bile Acid Production
Your liver uses cholesterol to produce bile acids. As emulsifying agents, bile acids help prepare dietary fats for digestion. Through a series of reactions, bile acids are converted into bile salts and combine with various compounds, including a phospholipid called lecithin. The resulting watery mixture, called bile, then goes to the gallbladder for storage, if it is not needed for digestion. Otherwise, it passes directly to the intestines. Champe and Harvey describe bile salts as the only significant way your body gets rid of excess cholesterol.
Vitamin D Synthesis
Your body also requires cholesterol to synthesize vitamin D. Champe and Harvey note that D vitamins mainly act on the kidneys, intestines and bones to restore adequate blood calcium levels whenever those levels become too low or too high. This regulation is necessary because calcium has many key functions, including bone strength, and the proper functioning of muscles and nerves. Severe vitamin D deficiency causes the classical malformations of the skeleton known as rickets in children, and osteomalacia in adults. However, less obvious effects may also occur because, as the Linus Pauling Institute notes, vitamin D also plays important roles in immunity, insulin secretion, blood pressure regulation and the specialization of cells for specific functions.
Transport
Cholesterol reaches various parts of your body through the bloodstream. However, because of its hydrophobic character, it must be associated with special carrier molecules, or dissolved in bile. These carrier molecules, known as lipoproteins, include high-density lipoproteins, or HDLs; low-density lipoproteins, or LDLs; chylomicrons; and very low-density lipoproteins, or VLDL. According to the Merck Manual, elevated HDL cholesterol levels lower your risk of heart disease and stroke because HDL removes cholesterol from your arteries and transports it back to the liver. On the other hand, LDL cholesterol increases your heart disease and stroke risk because LDL carries cholesterol away from the liver to various organs.
Side Effects
Your body typically produces the amount of cholesterol it needs and gets rid of excess quantities. However, the Merck Manual indicates that blood cholesterol levels can become abnormal for various reasons, including aging, certain hereditary conditions, use of certain drugs, high-fat diets, physical inactivity and excess weight. Cholesterol that accumulates in the blood contributes to plaque formation on the inner walls of your arteries, causing openings to narrow. This can slow or stop the blood flow in your arteries, potentially leading to a heart attack or stroke, says the American Heart Association.
References
- The Merck Manual: Cholesterol Disorders
- "Lippincott's Illustrated Reviews: Biochemistry"; Pamela Champe and Richard Harvey; 2006
- American Heart Association: Atherosclerosis
- University Institute of Psychiatry: Steroid Hormone Metabolism
- Linus Pauling Institute: Vitamin D
