What is Cholesterol? What Causes High Cholesterol?

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Main Category: Cholesterol
Also Included In: Statins;  Cardiovascular / Cardiology
Article Date: 28 May 2009 - 20:00 PDT

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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.

Symptoms of high cholesterol (hypercholesterolaemia)

Symptoms of high cholesterol do not exist alone in a way a patient or doctor can identify by touch or sight. Symptoms of high cholesterol are revealed if you have the symptoms of atherosclerosis, a common consequence of having high cholesterol levels. These can include:

• Narrowed coronary arteries in the heart (angina)


• Leg pain when exercising - this is because the arteries that supply the legs have narrowed.


• Blood clots and ruptured blood vessels - these can cause a stroke or TIA (mini-stroke).


• Ruptured plaques - this can lead to coronary thrombosis (a clot forming in one of the arteries that delivers blood to the heart). If this causes significant damage to heart muscle it could cause heart failure.


• Xanthomas - thick yellow patches on the skin, especially around the eyes. They are, in fact, deposits of cholesterol. This is commonly seen among people who have inherited high cholesterol susceptibility (familial or inherited hypercholesterolaemia).

What causes high cholesterol?

Lifestyle causes

• Nutrition - although some foods contain cholesterol, such as eggs, kidneys, eggs and some seafoods, dietary cholesterol does not have much of an impact in human blood cholesterol levels. However, saturated fats do! Foods high in saturated fats include red meat, some pies, sausages, hard cheese, lard, pastry, cakes, most biscuits, and cream (there are many more).


• Sedentary lifestyle - people who do not exercise and spend most of their time sitting/lying down have significantly higher levels of LDL (bad cholesterol) and lower levels of HDL (good cholesterol).


• Bodyweight - people who are overweight/obese are much more likely to have higher LDL levels and lower HDL levels, compared to people who are of normal weight.


• Smoking - this can have quite a considerable effect on LDL levels.


• Alcohol - people who consume too much alcohol regularly, generally have much higher levels of LDL and much lower levels of HDL, compared to people who abstain or those who drink in moderation.

Treatable medical conditions

These medical conditions are known to cause LDL levels to rise. They are all conditions which can be controlled medically (with the help of your doctor, they do not need to be contributory factors):

• Diabetes
• High blood pressure (hypertension)
• High levels of triglycerides
• Kidney diseases
• Liver diseases
• Under-active thyroid gland

Risk factors which cannot be treated

These are known as fixed risk factors:

• Your genes 1 - people with close family members who have had either a coronary heart disease or a stroke, have a greater risk of high blood cholesterol levels. The link has been identified if your father/brother was under 55, and/or your mother/sister was under 65 when they had coronary heart disease or a stroke.


• Your genes 2 - if you have/had a brother, sister, or parent with hypercholesterolemia (high cholesterol) or hyperlipidemia (high blood lipids), your chances of having high cholesterol levels are greater.


• Your sex - men have a greater chance of having high blood cholesterol levels than women.


• Your age - as you get older your chances of developing atherosclerosis increase.


• Early menopause - women whose menopause occurs early are more susceptible to higher cholesterol levels, compared to other women.


• Certain ethnic groups - people from the Indian sub-continent (Pakistan, Bangladesh, India, Sri Lanka) are more susceptible to having higher cholesterol levels, compared to other people.

How is high cholesterol diagnosed?

Cholesterol levels may be measured by means of a simple blood test. It is important not to eat anything for at least 12 hours before the blood sample is taken. The blood sample can be obtained with a syringe, or just by pricking the patient's finger.

The blood sample will be tested for LDL and HDL levels, as well as blood triglyceride levels. The units are measure in mg/dl (milligrams/deciliter) or 5mmol/liter (millimoles/liter).

People who have risk factors should consider having their cholesterol levels checked.

What are the treatments for high cholesterol?

Lifestyle

Most people, especially those whose only risk factor has been lifestyle, can generally get their cholesterol and triglyceride levels back to normal by:

• Doing plenty of exercise (check with your doctor)
• Eating plenty of fruits, vegetables, whole grains, oats, good quality fats
• Avoiding foods with saturated fats
• Getting plenty of sleep (8 hours each night)
• Bringing your bodyweight back to normal
• Avoiding alcohol
• Stopping smoking

Many experts say that people who are at high risk of developing cardiovascular disease will not lower their risk just by altering their diet. Nevertheless, a healthy diet will have numerous health benefits.

Cholesterol-controlling medications

If your cholesterol levels are still high after doing everything mentioned above, your doctor may prescribe a cholesterol-lowering drug. They may include the following:

• Statins (HMG-CoA reductase inhibitors) - these block an enzyme in your liver that produces cholesterol. The aim here is to reduce your cholesterol levels to under 4 mmol/liter and under 2 mmol/liter for your LDL. Statins are useful for the treatment and prevention of atherosclerosis. Side effects can include constipation, headaches, abdominal pain, and diarrhea. Atorvastatin, fluvastatin, lovastatin, pravastatin, rosuvastatin and simvastatin are examples of statins.


• Aspirin - this should not be given to patients under 16 years of age.


• Drugs to lower triglyceride levels - these are fibric acid derivatives and include gemfibrozil, fenofibrate and clofibrate.


• Niacin - this is a B vitamin that exists in various foods. You can only get very high doses with a doctor's prescription. Niacin brings down both LDL and HDL levels. Side effects might include itching, headaches, hot flashes (UK: flushes), and tingling (mostly very mild if they do occur).


• Anti hypertensive drugs - if you have high blood pressure your doctor may prescribe Angiotensin-converting enzyme (ACE) inhibitors, Angiotensin || receptor blockers (ARBs), Diuretics, Beta-blockers, Calcium channel blockers.

In some cases cholesterol absorption inhibitors (ezetimibe) and bile-acid sequestrants may be prescribed. They have more side effects and require considerable patient education to achieve compliance (to make sure drugs are taken according to instruction).

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Written by Christian Nordqvist

Original article date: 05 June 2004
Article updated: 28 May 2009


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