The True Facts About Cholesterol

Cholesterol is a waxy steroid metabolite found in the cell membranes and transported in the blood plasma of all animals. It is an essential structural component of human cell membranes, where it is required to establish proper membrane permeability and fluidity. In addition, cholesterol is an important component for the manufacture of bile acids, steroid hormones, and several fat-soluble vitamins. Cholesterol is the principal sterol synthesized by animals, but small quantities are synthesized in other eukaryotes, such as plants and fungi. It is almost completely absent among prokaryotes, which include bacteria.

Cholesterol is essential component of cell membranes and therefore primarly synthesized from simpler substances within the body. Despite its importance for human life, high levels of cholesterol in blood, depending on how it is transported within lipoproteins, are strongly associated with progression of atherosclerosis. Lipoproteins consist from proteins and fats and are responsible for transport of fats in blood circulation system. Their quantity in blood depends on eating habits, person’s weight, age, stress level and hormone activity. In addition to providing a soluble means for transporting cholesterol through the blood, lipoproteins have cell-targeting signals that direct the lipids they carry to certain tissues. For this reason, there are several types of lipoproteins within blood called, in order of increasing density, chylomicrons, very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL). The more cholesterol and less protein a lipoprotein has the less dense it is. The cholesterol within all the various lipoproteins is identical, although some cholesterol is carried as the “free” alcohol and some is carried as fatty acyl esters referred to as cholesterol esters. However, the different lipoproteins contain apolipoproteins, which serve as ligands for specific receptors on cell membranes. In this way, the lipoprotein particles are molecular addresses that determine the start- and endpoints for cholesterol transport.

VLDL molecules are produced by the liver and contain excess triacylglycerol and cholesterol that is not required by the liver for synthesis of bile acids. During transport in the bloodstream, the blood vessels cleave and absorb more triacylglycerol to leave IDL molecules, which contain an even higher percentage of cholesterol. The IDL molecules have two possible fates: Half are taken up by the liver for metabolism into other biomolecules and the other half continue to lose triacylglycerols in the bloodstream until they form LDL molecules, which have the highest percentage of cholesterol within them. LDL molecules, therefore, are the major carriers of cholesterol in the blood, and each one contains approximately 1,500 molecules of cholesterol ester. Within the cell, the cholesterol can be used for membrane biosynthesis or esterified and stored within the cell, so as to not interfere with cell membranes.

When the cell has abundant cholesterol, LDL receptor synthesis is blocked so that new cholesterol in the form of LDL molecules cannot be taken up. On the converse, more LDL receptors are made when the cell is deficient in cholesterol. When this system is deregulated, many LDL molecules appear in the blood without receptors on the peripheral tissues. These LDL molecules are oxidized and taken up by macrophages, which become engorged and form foam cells. These cells often become trapped in the walls of blood vessels and contribute to artherosclerotic plaque formation. These plaques are the main causes of heart attacks, strokes, and other serious medical problems, leading to the association of so-called LDL cholesterol (actually a lipoprotein) with “bad” cholesterol. Also, HDL particles are thought to transport cholesterol back to the liver for excretion or to other tissues that use cholesterol to synthesize hormones in a process known as reverse cholesterol transport (RCT). Having large numbers of large HDL particles correlates with better health outcomes. In contrast, having small numbers of large HDL particles is independently associated with atheromatous disease progression within the arteries.

Several studies in last years have shown that cholesterol, which is taken in to the body with the food, doesn’t have much influence on the quantity of in-body-formed cholesterol. The fact is, 75 percent of cholesterol in blood originate from in-body formation and only 25 percent of it originates from the food source. Therefore, almost 90 percent of high-level cholesterol related diseases are connected with hereditary origins.

The desirable LDL level is considered to be less than 100 mg/dL (2.6 mmol/L), although a newer target of < 70 mg/dL can be considered in higher risk individuals based on some of the above-mentioned trials. A ratio of total cholesterol to HDL—another useful measure—of far less than 3.5:1 is thought to be healthier. Of note, typical LDL values for children before fatty streaks begin to develop is 35 mg/dL.

About the Author:

Mark Hanselich, MPharm - I try to be as versatile as possible. I graduated in pharmacy, work as journalist, play soccer, have my own wine cellar and can communicate in six languages. I'm also personal development author and internet marketing specialist. Together with Mr. Daniel Maxoff I run the Website Anioc.com, dedicated to personal development, health and all the good things in our lives. You can also follow me on Twitter.