What is Cholesterol? What Causes High Cholesterol?

Cholesterol is a fat (lipid) which is produced by the liver and is crucial for normal body functioning. Cholesterol exists in the outer layer of every cell in our body and has many functions. It is a waxy steroid and is transported in the blood plasma of all animals. It is the main sterol synthesized by animals - small amounts are also synthesized in plants and fungi. 

The word "cholesterol" comes from the Greek word chole, meaning "bile", and the Greek word stereos, meaning "solid, stiff".

What are the functions of cholesterol?

• It builds and maintains cell membranes (outer layer), it prevents crystallization of hydrocarbons in the membrane
• It is essential for determining which molecules can pass into the cell and which cannot (cell membrane permeability)
• It is involved in the production of sex hormones (androgens and estrogens)
• It is essential for the production of hormones released by the adrenal glands (cortisol, corticosterone, aldosterone, and others)
• It aids in the production of bile
• It converts sunshine to vitamin D
• It is important for the metabolism of fat soluble vitamins, including vitamins A, D, E, and K
• It insulates nerve fibers

There are three main types of lipoproteins

Cholesterol is carried in the blood by molecules called lipoproteins. A lipoprotein is any complex or compound containing both lipid (fat) and protein. The three main types are:

• LDL (low density lipoprotein) - people often refer to it as bad cholesterol. LDL carries cholesterol from the liver to cells. If too much is carried, too much for the cells to use, there can be a harmful buildup of LDL. This lipoprotein can increase the risk of arterial disease if levels rise too high. Most human blood contains approximately 70% LDL - this may vary, depending on the person.


• HDL (high density lipoprotein) - people often refer to it as good cholesterol. Experts say HDL prevents arterial disease. HDL does the opposite of LDL - HDL takes the cholesterol away from the cells and back to the liver. In the liver it is either broken down or expelled from the body as waste.


• Triglycerides - these are the chemical forms in which most fat exists in the body, as well as in food. They are present in blood plasma. Triglycerides, in association with cholesterol, form the plasma lipids (blood fat). Triglycerides in plasma originate either from fats in our food, or are made in the body from other energy sources, such as carbohydrates. Calories we consume but are not used immediately by our tissues are converted into triglycerides and stored in fat cells. When your body needs energy and there is no food as an energy source, triglycerides will be released from fat cells and used as energy - hormones control this process.

What are normal cholesterol levels?

The amount of cholesterol in human blood can vary from 3.6 mmol/liter to 7.8 mmol/liter. The National Health Service (NHS), UK, says that any reading over 6 mmol/liter is high, and will significantly raise the risk of arterial disease. The UK Department of Health recommends a target cholesterol level of under 5 mmo/liter. Unfortunately, two-thirds of all UK adults have a total cholesterol level of at least five (average men 5.5, average women 5.6). 

Below is a list of cholesterol levels and how most doctors would categorize them in mg/dl (milligrams/deciliter) and 5mmol/liter (millimoles/liter).

• Desirable - Less than 200 mg/dL
• Bordeline high - 200 to 239 mg/dL
• High - 240 mg/dL and above


• Optimum level: less than 5mmol/liter
• Mildly high cholesterol level: between 5 to 6.4mmol/liter
• Moderately high cholesterol level: between 6.5 to 7.8mmol/liter
• Very high cholesterol level: above 7.8mmol/liter

Dangers of high cholesterol levels

High cholesterol levels can cause:

• Atherosclerosis - narrowing of the arteries.


• Higher coronary heart disease risk - an abnormality of the arteries that supply blood and oxygen to the heart.


• Heart attack - occurs when the supply of blood and oxygen to an area of heart muscle is blocked, usually by a clot in a coronary artery. This causes your heart muscle to die.


• Angina - chest pain or discomfort that occurs when your heart muscle does not get enough blood.


• Other cardiovascular conditions - diseases of the heart and blood vessels.


• Stroke and mini-stroke - occurs when a blood clot blocks an artery or vein, interrupting the flow to an area of the brain. Can also occur when a blood vessel breaks. Brain cells begin to die.

If both blood cholesterol and triglyceride levels are high, the risk of developing coronary heart disease rises significantly.

Medical Treatment

If following a low-saturated fat, low-cholesterol diet, increasing physical activity, and losing weight have not lowered the risk for developing coronary heart disease after about 3 months, your doctor may consider prescribing a cholesterol-lowering medication. If your doctor prescribes medicine, you must still:

1. follow your cholesterol-lowering diet;
   
   
2. be more physically active;
   
   
3. lose weight if you are overweight; and 
   
   
4. control or stop all of your other coronary heart disease risk factors (including controlling high blood pressure and diabetes, and quit smoking).

Taking all these steps together may lessen the amount of medicine a person needs or make the medicine work better, which reduces the risk for developing coronary heart disease. The doctor may prescribe medication from the following categories:

Statins: Statins lower LDL cholesterol levelsmore than other type of drug. They lower cholesterol by slowing down the production of cholesterol and by increasing the liver's ability to remove the LDL cholesterol already in the blood.

• Studies using statins have reported 20%-60% lower LDL cholesterol levels in people taking them. Statins also reduce high triglyceride levels modestly, and produce a mild increase in HDL cholesterol.
  
  
• Results from statin medications are seen after several weeks. After 6-8 weeks, a patient's doctor may recheck blood tests. A second measurement of LDL cholesterol level must be averaged with the first to help adjust medication dosing.
  
  
• Statins are well tolerated, and serious side effects are rare. Rarely, widespread muscle breakdown, known as rhabdomyolysis, may occur. The symptoms include diffuse muscle pain, weakness, and dark colored urine.This may signal a medical emergency: if you develop these symptoms, stop taking the statin medication and contact your health care practitioner immediately.
  
  
• Other side effects may include an upset stomach, gas, constipation, andabdominal pain or cramps. These symptoms are usually mild to moderate and generally go away as your body adjusts to the medication.
  
  
• Monitoring of liver function by blood tests is usually ordered in patients taking statins.
  
  
• There are many statin drugs (available by prescription). The choice made by the health care practitioner and patient will depend upon the clinical situation. Examples include:
  
  
  • atorvastatin (Lipitor),
    
    
  • fluvastatin (Lescol),
    
    
  • lovastatin (Mevacor, Altocor),
    
    
  • pravastatin (Pravachol),
    
    
  • simvastatin (Zocor), and
    
    
  • rosuvastatin (Crestor).

Bile acid sequestrants: These drugs bind with cholesterol-containing bile acids in the intestines and allow them to be eliminated in the stool. Bile acid sequestrants may lower LDL cholesterol by about 10%-20%. Bile acid sequestrants are sometimes prescribed with a statin to enhance cholesterol reduction.

• Cholestyramine (Questran, Questran Light), colestipol (Colestid), andcolesevelam (WelChol) are the three bile acid sequestrants currently available. These three drugs are available as powders or tablets and are are not absorbed from the gastrointestinal tract. 
  
  
• Bile acid sequestrant powders must be mixed with water or fruit juice and are taken once or twice daily with meals. Tablets must be taken with large amounts of fluids to avoid stomach and intestinal complaints including constipation, bloating, nausea, and gas.

Cholesterol absorption inhibitors: These drugs inhibit cholesterol absorption in the gut and has few, if any, side effects. Cholesterol absorption inhibitors may be rarely associated with tongue swelling (angioedema). Ezetimibe (Zetia) reduces LDL cholesterol by 18%-20%. It is probably most useful in people who cannot tolerate taking statins. When used in addition to a statin, ezetimibe is equivalent to doubling or tripling the statin dose.

Nicotinic acid or niacin: Nicotinic acid lowers total cholesterol, LDL cholesterol, and triglyceride levels, while raising HDL cholesterol levels.

• There are two types of nicotinic acid: immediate release and extended release.
  
  
• The immediate-release form of crystalline niacin is inexpensive and widely accessible without a prescription, but, because of potential side effects, it should not be used for cholesterol lowering without monitoring by a health care practitioner. (Nicotinamide, another form of niacin, does not lower cholesterol levels and should not be used in place of nicotinic acid.)
  
  
• Nicotinic acid reduces LDL cholesterol levels by 10%-20%, reduces triglycerides by 20%-50%, and raises HDL cholesterol by 15%-35%.
  
  
• A common and troublesome side effect of nicotinic acid is flushing or hot flashes, which are the result of blood vessels dilating. Most people develop a tolerance to flushing, which can sometimes be decreased by taking the drug during or after meals or by the use of aspirin or other similar medications prescribed by your doctor 30 minutes prior to taking niacin. The extended-release form may cause less flushing than the other forms.
  
  
• The effect of high blood pressure medicines may also be increased while taking niacin causing blood pressure to potentially drop. A variety of gastrointestinal symptoms, including nausea, indigestion, gas, vomiting,diarrhea, and peptic ulcers, have been experienced with the use of nicotinic acid. Other major side effects include liver problems, gout, and high blood sugar. 
  
  
• Extended-release niacin is often better tolerated than crystalline niacin. However, its liver toxicity (liver damage) is probably greater. The dose of extended-release niacin is usually limited to 2 grams per day.

Fibrates: These cholesterol-lowering drugs are effective in lowering triglycerides.

• gemfibrozil (Lopid),
  
  
• fenofibrate (Tricor), which is more effective at lowering triglycerides and LDL cholesterol.

Side effects of fibrates may include stomach or intestinal discomfort, gallstones, and may affect anticoagulation medication effects in thinning blood.