What is cholesterol?

Cholesterol is a waxy, fat-like substance found in all cells of the body. Cholesterol is also found in some of the foods that we eat. Our body does need cholesterol to make hormones, vitamin D, and substances that help digest foods. Since cholesterol is fatty, it does not mix with blood and is carried in small packages called lipoproteins. These basically contain fat or lipid inside and protein on the outside.

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:

  1.  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.

2. 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.

3. 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.

Causes of Cholesterol

Saturated fat in food raises LDL cholesterol levels. Trans fatty acids or trans fats from hydrogenated vegetable oil as well as foold from animal sources such as egg yolks, meat and cheese all contribute to raising LDL cholesterol levels.

Being overweight also raises LDL levels and lowers HDL levels and increases the total cholesterol level. Lack of regular exercise can cause weight gain and consequently raise cholesterol levels.

High blood cholesterol can also be due to heredity. An inherited genetic condition (familial hypercholesterolemia) results in very high LDL cholesterol levels. It begins at birth, and may result in a heart attack at an early age.

Age and gender also play a role in determining cholesterol levels. Younger men have lower levels of HDL than women while younger women have lower levels of LDL than men. As women and men get older, their LDL cholesterol levels rise. After 55, women have higher LDL cholesterol levels than men

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

What determines the level of LDL cholesterol in the blood?

The liver manufactures and secretes LDL cholesterol into the blood. It also removes LDL cholesterol from the blood by active LDL receptors on the surface of its cells. A decrease number of liver cell LDL receptors is associated with high LDL cholesterol blood levels.

Both heredity and diet have a significant influence on a person's LDL, HDL and total cholesterol levels. For example, familial hypercholesterolemia (hyper= more + cholesterol + emia= in blood) is a common inherited disorder whose victims have a diminished number or nonexistent LDL receptors on the surface of liver cells. People with this disorder also tend to develop atherosclerosis and heart attacks during early adulthood.

Diets that are high in saturated fats and cholesterol raise the levels of LDL cholesterol in the blood. Fats are classified as saturated or unsaturated (according to their chemical structure). Saturated fats are derived primarily from meat and dairy products and can raise blood cholesterol levels. Some vegetable oils made from coconut, palm, and cocoa are also high in saturated fats.

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).