Cholesterol - Sources of Origin
Cholesterol is a fat like substance (a lipid) that is an important part of the outer lining (membrane) of cells in the body of living beings. Cholesterol is also found in the blood circulation of humans. The origin of cholesterol in a person's blood comes form 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. After a meal, cholesterol is absorbed by the intestines into the blood circulation and is then packaged inside a protein coat. This cholesterol-protein coat complex is called a chylomicron.
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.
There are no established "normal" blood levels for total and LDL cholesterol. In most other blood tests in medicine, normal ranges can be set by taking measurements from large number of healthy subjects. For example, normal fasting blood sugar levels can be established by performing blood tests among healthy subjects without diabetes mellitus. If a patient's fasting blood glucose falls within this normal range, he/she most likely does not have diabetes mellitus, whereas if the patient's fasting blood sugar tests higher than the normal range, he/she probably has diabetes mellitus and further tests can be performed to confirm the diagnosis. Medications, such as insulin or oral diabetes medications can be prescribed to lower abnormally high blood sugar levels.
Unfortunately, the normal range of LDL cholesterol among "healthy" adults (adults with no known coronary heart disease) in the United States may be too high. The atherosclerosis process may be quietly progressing in many healthy adults with average LDL cholesterol blood levels, putting them at risk of developing coronary heart diseases in the future.