Cholesterol is often thought of as “bad” and to be avoided. However, the body requires cholesterol for nerve and cell function, including liver function, the production of the steroid hormones, including vitamin D, and the sex hormones.
The cholesterol in a person’s blood originates from two major sources: Dietary intake; and Liver production. Dietary cholesterol comes mainly from meat, poultry, fish, and dairy products. Organ meats, such as liver, are especially high in cholesterol content, while foods of plant origin contain no cholesterol.
The liver is capable of removing cholesterol from the blood circulation as well as manufacturing cholesterol and secreting cholesterol into the blood circulation. After a meal, the liver removes chylomicrons from the blood circulation. In between meals, the liver manufactures and secretes cholesterol back into the blood circulation.
Cholesterol is minimally soluble in water; it cannot dissolve and travel in the water-based bloodstream. This factor leads to atherosclerosis. Instead, cholesterol is transported in the bloodstream by lipoproteins. Lipoproteins are essentially protein “suitcases” that are water-soluble and carry cholesterol and fats internally. The proteins forming the surface of the given lipoprotein particle determine from what cells cholesterol will be removed and to where it will be supplied.
It is important to remember that the body can produce as much cholesterol as it needs, so dietary cholesterol should be limited to avoid overloading our systems.
To understand the problems with cholesterol, we need to look at how the body metabolizes it:
After a meal, cholesterol is absorbed by the intestines into the blood circulation. Triglycerides and cholesterol are coated with water-soluble protein and become a lipoprotein. This cholesterol-protein coat complex is called a chylomicron;
Chylomicrons are the largest lipoproteins, and they primarily transport fats from the intestinal mucosa to the liver. They carry mostly triglyceride fats and cholesterol (both from food and especially internal cholesterol secreted by the liver into the bile);
In the liver, chylomicron particles give up triglycerides and some cholesterol and are converted into low-density lipoprotein (LDL) particles, which carry triglycerides and cholesterol on to other body cells. When our dietary fat intake exceeds the optimal level, the cells become saturated with cholesterol. The LDL’s are unable to deposit their load anywhere but the artery walls, causing the formation of a hard, thick substance called cholesterol plaque. Over time, cholesterol plaque causes thickening of the artery walls and narrowing of the arteries, a process called atherosclerosis. LDL levels are usually low in healthy individuals and high LDL is strongly associated with promoting atheromatous disease within the arteries;
High-density lipoprotein (HDL) particles transport cholesterol back to the liver for excretion, but vary considerably in their effectiveness. When the cholesterol level is excessive, HDL’s cannot keep up and the arteries become clogged. Having high HDL correlates with better health outcomes and having low HDL is strongly associated with atheromatous disease progression within the arteries(6); and the cholesterol molecules present in LDL cholesterol and HDL cholesterol are identical. The difference between the two cholesterols derives from the carrier protein molecules (the lipoprotein) component.
Low Density Lipoproteins (LDL) cholesterol is called “bad” cholesterol Elevated LDL is associated with an increased risk of coronary heart disease High Density Lipoproteins HDL cholesterol is called the “good cholesterol” because HDL cholesterol particles prevent atherosclerosis by extracting cholesterol from the artery walls and disposing of them through the liver High LDL/HDL ratios are risk factors for atherosclerosis Low LDL/HDL ratios are desirable
Total Cholesterol: Total cholesterol is the sum of LDL, HDL, along with VLDL (very low density) cholesterol, and IDL (intermediate density) cholesterol. The liver not only manufactures and secretes LDL cholesterol into the blood; it also removes LDL cholesterol from the blood.
 Characterized by a lower density in grams per milliliter and a higher lipid (fat) content
 Lack of information on LDL particle number and size is one of the major problems of conventional lipid tests.
 Note that the concentration of total HDL does not indicate the actual number of functional large HDL particles, another of the major problems of conventional lipid tests.
 A high number of active LDL receptors on the liver surfaces are associated with the rapid removal of LDL cholesterol from the blood and low blood LDL cholesterol levels. A deficiency of LDL receptors is associated with high LDL cholesterol blood levels.
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