Wednesday, June 4, 2008

High Cholesterol (Hypercholesterolemia)



Cholesterol

Cholesterol is a sterol (a group of unsaturated alcohols of the steroid group) present in cell membranes, the brain and lipoproteins. It can be utilized to produce all the steroids of the body. About 1g of cholesterol is synthesized per day in humans. Cholesterol is normally converted into bile salts, vitamin D3 and steroid hormones, which includes testosterone, estrogen and progesterone. Cholesterol is mainly excreted in the form of bile salts in stool. Free cholesterol is transported by lipoproteins in the circulation. Cholesterol ester is a storage form of cholesterol found in most tissues. Cholesterol esters are formed by the esterification of cholesterol to fatty acids. This esterification occurs in the body by transfer of PUFA (polyunsaturated fatty acids). This step is important in the regulation of cholesterol level. The normal blood level is 150-220 mg/dL. Increased cholesterol levels lead to atherosclerosis as cholesterol accumulates in the arteries causing narrowing of blood vessels. Dietary intake of polyunsaturated fatty acids help in the transport and metabolism of cholesterol and, in so doing, prevents atherosclerosis.

Note that hypercholesterolemia is more common in men younger than 55 and in women older than 55 years. The risk for high cholesterol increases with age.

Causes

With more than enough cholesterol in the bloodstream, which is usually due to an unbalanced diet, cholesterol is carried throughout the blood bound to proteins along with a few other substances, e.g fatty acids, and is called a lipoprotein. Lipoproteins can directly contribute to atherosclerosis progression. The main types of lipoproteins are: Low-density lipoprotein (LDL), which is also known as 'bad cholesterol' and is responsible for transporting cholesterol throughout the body, and High-density lipoprotein (HDL), which transports cholesterol from the bodily tissues back to the liver for excretion. With an adequately balanced diet, the HDL and LDL levels can be altered to maintain acceptable cholesterol levels. Increasing the intake of linoleic acid (and other related polyunsaturated fatty acids) lowers cholesterol levels, although not as significantly as saturated fatty acids raise it.

Other factors that influence the amount of 'bad cholesterol' in the blood include genetics, body weight, viscous dietary fiber, soy protein, plant sterols, antioxidants and flavonoids (fat-soluble antioxidants). In a rare cholesterol disorder, the NPC(Neiman-Pick type C)1 gene malfunctions impairing the normal movement of cholesterol within cells. The genetic makeup of a person may change the way LDL cholesterol is removed or cause the liver to produce too much cholesterol. Being overweight tends to increase cholesterol and so, losing weight can help lower LDL and total cholesterol levels, as well as raise HDL and lower triglyceride levels. Oxygen free radicals (hydrogen peroxide, superoxide, etc) are sometimes generated by cellular activities of the body. These compounds bring about damage to blood vessels by oxidizing/altering lipids (primarily LDL) and turning certain cells called macrophages into foam cells, which contribute to plaque formation in blood vessels. Water-soluble antioxidants, e.g Vitamin C, and fat-soluble antioxidants protect against free radicals.

Risk Factors

  • Cigarette smoking damages the walls of blood vessels making them more susceptible/vulnerable to fatty deposit accumulation. Smoking may also lower HDL cholesterol levels, which is the 'good cholesterol'.

  • High blood pressure can damage arteries, contributing to the rate of fatty deposit accumulation.

  • High blood sugar alters LDL and HDL cholesterol levels (LDL cholesterol becomes high while HDL cholesterol becomes low). High blood sugar can also damage the lining of arteries.

Treatment

After having a blood test to determine a complete lipid profile, which measures total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides, and hypercholesterolemia is evident, the choices of medication include:

  • Statins - prevent the liver from making cholesterol and with this cholesterol is depleted in the liver cells, allowing them to take up cholesterol for excretion. They may also aid in reabsorbing fatty deposits that may have accumulated in the wall of arteries.

Examples: atorvastatin (Lipitor), fluvastatin (Lescol), lovastatin (Altoprev, Mevacor), pravastatin (Pravachol), rosuvastatin (Crestor) and simvastatin (Zocor).

  • Bile-acid-binding resins -binds to bile acids produced by the liver, preventing them from being recycled. This causes cholesterol to be taken up by the liver cells to be converted to bile acids, reducing blood cholesterol levels in the process.

Examples: Cholestyramine (Prevalite, Questran), colesevelam (Welchol) and colestipol (Colestid).

  • Cholesterol absorption inhibitors- prevents the absorption of cholesterol by the small intestine.

Example: ezetimibe (Zetia), which can be used in combination with any of the statin drugs.

For high triglycerides:

  • Fibrates- decrease triglycerides by reducing the production of very-low-density lipoprotein (VLDL), precursor to LDL (meaning that VLDL is used to make LDL), and by speeding up the removal of triglycerides from the blood. Triglycerides are the major component of VLDL.

  • Niacin (Niaspan)- decreases triglycerides by limiting the production of VLDL and LDL by the liver.

Most medications do not cause complications. However, the most common side effects are constipation, diarrhea, stomach pain and nausea.

Why Is A Change In Lifestyle Important?

Lifestyle changes can improve your cholesterol level significantly. Regular physical activity can help raise HDL and lower LDL and is especially important for those with high triglyceride and/or low HDL levels who are overweight with a large waist. Weight management plays a central role in prevention of cardiovascular diseases. Dietary recommendations include saturated and trans fatty acid intake less than or equal to 8% of total calories; cholesterol intake less than 300 mg/day; at least 2 servings of fish per week; a diet which includes fruits,vegetables, and whole grains; limiting sodium intake to less than 2300mg/day; limiting alcohol to 2 drinks or less per day for men and 1 drink per day for women; and limiting added sugar. This healthy eating pattern should assist in acheiving desirable body weight, cholesterol and lipoprotein profile and blood pressure. Lifestyle changes can reduce excessive LDL concentrations by 20-40%. For this reason, lifestyle changes are essential in the treatment process.

5 comments:

Health Advocate said...

This is quite a comprehensive posting on cholesterol and its levels. It would give us a lot of insight on this aspect of health.

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