Cholesterol (chole- bile and stereos- solid) is a type of lipid (fat) in your blood. It is vital for the body as it is required to build and maintain cell membranes and acts as a precursor for the biosynthesis of steroid hormones, bile acids, and vitamin D.
Sources of Cholesterol
Cholesterol comes from two sources:
• Your body: Your liver and other cells in your body make about 75 percent of blood cholesterol.
• Food: The remaining 25 percent comes from the food you eat (known as dietary cholesterol). Cholesterol is mostly found in animal products. Main dietary sources of cholesterol include cheese, egg yolks, beef, pork, poultry, fish, and shrimp. Human breast milk also contains significant quantities of cholesterol.
Cholesterol and Lipoproteins
Cholesterol being a type of lipid (fat) is insoluble in water and therefore, it is incapable of dissolving in blood (which is mostly water). To be carried in the blood, cholesterol combines with specific proteins to form a substance known as a lipoprotein. There are various kinds of lipoproteins in the body that carry cholesterol:
• LDL (Low-density lipoproteins) cholesterol carries cholesterol from the liver to cells of the body. It is also known as 'bad cholesterol' as it is the main source of cholesterol buildup and blockage in the arteries.
An LDL-cholesterol level of less than 100 mg/dL is considered optimal and has a very low risk for Coronary heart diseases (CHD). LDL levels between 100-129 mg/dL puts you at a higher risk of developing atherogenesis and may accelerate if your LDL levels exceed more than 190mg/dL.
• HDL (High-density lipoproteins) cholesterol carries cholesterol away from the arteries and back to the liver, where it's removed from your body. It is also known as 'good cholesterol' as it removes excess cholesterol from an arterial plaque, slowing its build-up and protects against heart attack.
That's the reason why high levels of HDL cholesterol (more than 60mg/dL) are believed to have beneficial effects in protecting against heart attack. On the other hand, low levels of HDL cholesterol (less than 40 mg/dL for men and less than 50mg/dL for women) may increase your risk of heart disease.
• Very low density lipoprotein (VLDL) cholesterol: They are triglyceride-rich lipoproteins that enable cholesterol to move within the water-based solution of the bloodstream. Some forms of VLDL appear to promote plaque buildup (atherosclerosis), similar to LDL (bad) cholesterol
• Chylomicrons: They are triglyceride-rich lipoproteins and are formed in the intestine from dietary fat and appear in the blood after a fat-containing meal and probably contribute to some extent in plaque formation.
Triglycerides are a kind of fat found in your blood and fat tissues. Triglycerides are not cholesterol, but are commonly measured along with cholesterol. Often, high triglycerides occur along with high total cholesterol, including high LDL (bad) cholesterol and low HDL (good) cholesterol.
Triglycerides that are rich in lipoproteins, [known as Triglyceride Rich Lipoproteins (TGRLP)] are of two types: Very Low Density Lipoproteins (VLDL) and Intermediate Density Lipoproteins (IDL). VLDL transports triglycerides to the adipose tissue and muscles. The triglycerides in VLDL are removed from the capillaries by the enzyme lipoprotein lipase, and the VLDL returns to the circulation as a smaller particle with a new name, intermediate-density lipoprotein (IDL).
VLDL and IDL are cholesterol- enriched particles and have many of the properties of LDL and contribute towards hardening and narrowing of your arteries. This puts you at risk of having a heart attack or stroke.
Elevated triglycerides are generally caused due physical inactivity, cigarette smoking, excess alcohol consumption, and a diet very high in carbohydrates (60 percent of total calories or more). However, some diseases such as, diabetes, obesity, or kidney failure can also cause high triglycerides.
The National Cholesterol Education Program Guidelines for Triglycerides
Importance of Cholesterol/ Complications of High Cholesterol
Your blood cholesterol level is directly related to various heart diseases. High levels of cholesterol in the blood can increase your risk of heart attack. When too much LDL (bad) cholesterol circulates in the blood, it can slowly build up in the inner walls of the arteries that feed the heart and brain. Together with other substances, it can form plaque, a thick, hard deposit that can narrow the arteries and make them less flexible. This condition is known as "atherosclerosis".
Plaque (atherosclerosis) makes the arteries narrow, which causes stress on other organs, such as the heart and the kidneys because of reduced blood flow. Many times, the plaque ruptures (breaks) resulting in formation of a clot. If a clot blocks a narrowed artery, it may result into a:
• Heart attack (if blood supply to heart is restricted) or
• Stroke (if blood supply to brain is restricted).
• Sedentary Lifestyle: Exercise plays a vital role in increasing your body's HDL levels and decreasing LDL levels. People who do not exercise at a regular basis and spend most of their time sitting/lying down can have significantly higher levels of LDL (bad cholesterol) and lower levels of HDL (good cholesterol).
• Smoking: Cigarette smoking is one of the major risk factors for heart disease. It damages the thin lining of blood vessels making it more prone to accumulation of fatty deposits.
• Family history of heart disease: If your parent or siblings have any of the heart disease before age 55, then you are at a greater risk of having high cholesterol levels.
• Obesity: If you are overweight/ obese, then you are more likely to have higher LDL and lower HDL levels as compared to people who are of normal weight.
• Nutrition: Some foods that are rich in cholesterol, such as seafood (shrimp, crawlfish or crayfish) red meat, some pies, sausages, hard cheese, lard, pastry, increase your cholesterol levels to a greater extent.
1. Cholesterol at the US National Library of Medicine Medical Subject Headings(MeSH). http://www.nlm.nih.gov/mesh/. Accessed April 25, 2013.
2. Hanukoglu I (Dec 1992). "Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis." J Steroid Biochem Mol Biol 43 (8): 779–804
3. Jensen RG et al. Lipids of human milk and infant formulas: a review. Am J ClinNutr 31 (6): 990–1016.
4. Triglycerides. http://www.heart.org/HEARTORG/GettingHealthy/NutritionCenter/Triglycerid.... Accessed April 26, 2013.
5. Huffman KM, et al. Exercise effects on lipids in persons with varying dietary patterns - does diet matter if they exercise? American Heart Journal. 2012;164:117.
6. Chapman MJ, et al. Triglyceride-rich lipoproteins and high-density lipoprotein cholesterol in patients at high risk of cardiovascular disease: Evidence and guidance for management. European Heart Journal. 2011;32:1345.
7. What is cholesterol? National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/health-topics/topics/hbc/. Accessed April 24, 2012.
8. About Cholesterol. http://www.heart.org/HEARTORG/Conditions/Cholesterol/Cholesterol_UCM_001.... Accessed April 24, 2013.