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).
[Also see below.]
- 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.
More info., reference:
The facts about cholesterol levels, [theirs, anyway]
CSIRO is carrying out research to develop strategies for reducing cholesterol levels, the risk of heart disease and other conditions that are food-related and correctable through modifying our diet.
- 14 June 2011 | Updated 14 October 2011
- What is it?
- Why is high cholesterol a problem?
- Cholesterol – the good and the bad
- What to do if your cholesterol level is high
- How high is high?
- What about triglycerides?
- How can I lower my triglyceride?
CSIRO is carrying out research in a number of dietary areas to develop strategies for reducing cholesterol levels, the risk of heart disease and other conditions that are food-related and correctable through modification of diet.
High levels of cholesterol are a risk factor for coronary artery disease (heart attacks and angina).
Cholesterol is an essential type of fat that is carried in the blood.
All cells in the body need cholesterol for internal and external membranes.
It is also needed to produce some hormones and for other functions.
The body generally makes all the cholesterol it needs.
Some dietary cholesterol is normally excreted via the liver, however eating too much saturated fat leads to excess cholesterol in the blood stream.
High levels of cholesterol in the blood stream are a risk factor for coronary artery disease (heart attacks and angina).
If your cholesterol level is 6.5 mmol/L or greater your risk of heart disease is about 4 times greater than that of a person with a cholesterol level of 4 mmol/L.
Not all people with high cholesterol levels get heart disease.
About 30 per cent of the community will die of heart disease and most of these will be over 65 years old.
Heart disease usually takes 60-70 years to develop, but if you discover your cholesterol level is high you should see your doctor within the next 2-3 months, not necessarily tomorrow.
Other risk factors for heart disease include smoking, high blood pressure and obesity.
Cholesterol is carried in the blood stream in particles called lipoproteins.
These are named according to how big they are:
the very large particles are called Very Low Density Lipoproteins (VLDL)
the intermediate size ones are called Low Density Lipoprotein (LDL) and these particles cause heart disease
the smallest particles are called High Density Lipoproteins (HDL) and these particles actually protect against heart disease.
The most effective way to lower your cholesterol is to reduce the amount of animal fat in your diet by various means.
reduce cheese intake and/or substitute low fat varieties
choose reduced fat milks
use polyunsaturated or monounsaturated margarine or oils instead of butter
choose lean cuts of meat and remove all visible fat
eat skinless chicken, fish or beans
beware of pies, pasties, fish and chips and commercial cakes (hidden fat)
make cakes at home with polyunsaturated fat, cook chips with polyunsaturated or monounsaturated oil
lose weight if overweight.
If you make a number of changes to your diet you can expect your cholesterol to fall by 10 per cent.
About 15 per cent of people will see no change and another 15 per cent will see changes of 20-30 per cent.
If your cholesterol is between 5.5 and 6.5 your risk of heart disease is only increased by a small amount.
Don’t panic but make a few moderate changes to your diet.
However if you already have heart disease, or one of your parents developed heart disease at an early age, (less than 55 years of age) then you need to make bigger changes.
If your cholesterol is higher than 6.5 then you need to make more changes.
If despite changes to your diet your cholesterol level remains above 6.5 you may need medication, especially if you have the other risk factors mentioned or you have a family history of heart disease- see your doctor.
Triglycerides are a stored energy source.
Most of the triglyceride is found in the very large particles, the VLDL.
Under some circumstances high blood triglyceride can be a risk factor.
If your cholesterol is high (greater than 6.5) and your HDL cholesterol is low (less than 0.9) then triglycerides can increase the risk of heart disease if they are greater than 1.7.
Triglyceride levels greater than 10 can cause inflammation of the pancreas which is a very serious condition.
Reduce your intake of animal or hard vegetable fats, lose weight and reduce alcohol intake.
Alcohol is very powerful at elevating triglyceride.
See your family doctor if it remains elevated as you may require medication.
Practicing pathology company, Healthscope, Melbourne, Australia:
Guideline levels: HDL >1.0 mmol/L; LDL <2.5 mmol/L; Triglyceride <1.5 mmol/L
“If your cholesterol is high (greater than 6.5) and your HDL cholesterol is low (less than 0.9) then triglycerides can increase the risk of heart disease if they are greater than 1.7.” (CSIRO)