People are constantly warned about the dangers of high cholesterol. TV commercials bombard the public with cholesterol-lowering drugs, foods and supplements. It would be easy to assume that cholesterol is always bad. But even though the dangers of high cholesterol are well known, it also plays a necessary part in the functioning of a healthy body.
Cholesterol is a type of lipid (fat) molecule that is either manufactured in the liver or acquired when meats, eggs or dairy products are eaten. Since cholesterol does not dissolve well in water, it is carried through the body in particles called lipoproteins. Lipoproteins consist of cholesterol, proteins, phospholipids and triglycerides.
How the Body Uses Cholesterol
Cholesterol, along with phospholipids, gives flexibility to the cell membrane. It also helps control the selective permeability of the cell, which means it helps determine which substances can enter the cell and which are kept out.
Cholesterol is one of the building blocks for the bile produced by the liver. Bile breaks down fats and aids in the absorption of fat-soluble vitamins in the intestines. Hormones--both the sex hormones like estrogen and progesterone, and the adrenal hormones like cortisol--are manufactured from a cholesterol base.
High-density lipoprotein (HDL) has been nicknamed "good cholesterol" by health professionals. Lipoproteins are made of cholesterol molecules along with molecules of fat and protein. The main function of HDL is to transport cholesterol molecules through the blood stream back to the liver. Along the way, HDL will retrieve low-density lipoproteins (LDL) and very low density lipoproteins (VLDL) from the artery walls. LDL and VLDL are the so-called "bad cholesterol" that forms plaques, or blockages, on the walls of the blood vessels.
Effects of High Cholesterol
The term "high cholesterol" is not a very accurate name. The cholesterol molecules contained in HDL, LDL, and VLDL are the same. The lipoproteins are distinguished by their size, function and the amount of proteins they contain.
In medical terms, high cholesterol means that a person's VLDL and LDL levels are too high, and their HDL levels are too low. VLDL and LDL are the lipoproteins that carry cholesterol and phospholipids from the liver to the tissues of the body that need them. But when there is more VLDL and LDL circulating than the body needs, these particles can form plaques on the walls of the blood vessels.
Plaques will slow down and eventually block the blood flow in a vessel, but they also can rupture and become lodged at a more narrow part of the artery. When a plaque ruptures and becomes lodged, it is known as an embolism. Embolisms that occur in the arteries of the heart cause heart attacks. An embolism that occurs in the brain is one of the causes of stroke.
References
- Basic and Clinical Pharmacology; Bertram Katzung; 2007
- Clinical Pharmacy and Therapeutics; Eric T. Herfindal, Dick R. Gourley and Linda Lloyd Hart; 1992
- Phospholipids and Cholesterol
