High blood cholesterol levels increase the risk of heart disease and stroke. Changes to diet, regular exercise and other lifestyle changes can reduce cholesterol levels In some cases, people with persistent high blood cholesterol may be treated with cholesterol-lowering medication.
New Zealanders have some of the highest average cholesterol levels in the world and 17% of all deaths in New Zealand can be related to high cholesterol. It is estimated that 90% of adult New Zealanders would benefit from lowering their cholesterol levels.
General information and causes
Cholesterol is a white, waxy substance that is circulated in the blood and is essential for life. It helps to build cell walls and is used in the manufacture of some hormones.
When there is more cholesterol circulating in the blood than the body needs, it can deposit onto the artery walls, eventually leading to narrowing and hardening of the arteries. This process is known as atherosclerosis and increases the risk of heart disease and stroke. This risk is compounded when other risk factors such as high blood pressure and a family history of heart disease are also present.
Your liver typically produces approximately 75% of the cholesterol circulating in your blood - a diet high in saturated fat stimulates the liver to produce more cholesterol.
The remaining 25% of your cholesterol is derived from the food you eat. This dietary cholesterol is present in animal foods – mainly in dairy products, meat, egg yolks, offal and shellfish. It is not present in plant foods.
For these reasons, the saturated fat and cholesterol content of the food you eat are likely to have a strong influence on your blood cholesterol levels.
Other factors that may influence your blood cholesterol levels include:
- Genetic susceptibility to high cholesterol
- Medical conditions such as diabetes and liver or thyroid disorders
- Being overweight
- Physical inactivity
- High stress levels.
“Good” and “bad” cholesterol
Cholesterol is circulated in the blood by substances called lipoproteins, notably:
- Low density lipoprotein (LDL)
- High density lipoprotein (HDL)
In simple terms, LDL cholesterol is considered “bad” because when there’s too much of it circulating in your blood it contributes to plaque build-up that clogs arteries and makes them less flexible (ie atherosclerosis). Treatment for high cholesterol will therefore aim to reduce LDL levels in your blood.
HDL cholesterol is considered “good” because it carries LDL cholesterol away from the arteries and back to the liver, where it is broken down and passed from the body. Treatment will therefore aim to ensure HDL levels are increased or maintained at healthy levels.
When blood cholesterol levels are assessed, triglyceride levels are also measured. Triglycerides are the most common type of fat that exists in food and in the body. When calories ingested in a meal are not used immediately by the body, they are converted to triglycerides and are transported to the fat cells to be stored. It is thought that elevated triglyceride levels may increase the risk of developing heart disease, particularly when associated with high LDL cholesterol levels.
Testing for high cholesterol
A simple blood test to assess cholesterol levels can be taken by a family doctor or at a medical clinic. Other risk factors for heart disease should also be assessed at the same time. A sample of blood is taken from a vein and is sent to a laboratory for testing. Cholesterol tests may be done using a finger prick of blood, however this is not as accurate as testing blood from a vein.
Blood cholesterol tests can be "fasting" or "non-fasting". Fasting tests require the person not to have eaten for a period of time prior to the test being taken and give more accurate results than non-fasting tests.
New Zealand health guidelines for acceptable blood cholesterol levels are:
- Total cholesterol – less than 4.0 mmol/L
- LDL cholesterol – less than 2.0 mmol/L
- HDL cholesterol – greater than 1.0 mmol/L
- TC/HDL ratio – less than 4.0
- Triglycerides – less than 1.7 mmol/L
The total cholesterol (TC) result indicates the total amount of all the different kinds of cholesterol in the blood stream. The TC/HDL ratio is used to calculate the risk of heart attack or stroke.
In cases of severely high cholesterol levels, cholesterol may deposit in other parts of the body such as the upper eyelids (xanthelasma) and at the back of ankles or in front of knees (xanthoma). White rings around the iris of the eye (corneal arcus) may also be an indicator of very high cholesterol levels.
Diet and lifestyle changes
Treatment typically aims to decrease the total cholesterol level by decreasing LDL cholesterol levels while maintaining or increasing HDL cholesterol levels.
LDL cholesterol levels are best decreased by reducing the intake of saturated fat, while HDL cholesterol levels are best increased by exercise, substituting saturated fats with polyunsaturated or monounsaturated fat, and maintaining a healthy weight. Triglyceride levels are best reduced by eating less sugar-containing foods, limiting alcohol intake, and by reducing the intake of total fat.
Recommended dietary changes will normally include:
- Reducing the total amount of fat in the diet, especially saturated fats (found mainly in animal products such as fatty meat, butter, high-fat milk, cream, and dripping)
- Eating generous amounts of fruit, vegetables, and fibre. It is thought that certain types of fibre such as legumes, oats, fresh fruit, and vegetables can reduce cholesterol levels
- Eating complex carbohydrates such as cereals and root vegetables (kumara, potatoes) instead of fat.
Other lifestyle changes should include:
- Exercising regularly (at least 30 minutes duration three times per week)
- Not smoking
- Maintaining a healthy body weight
- Limiting alcohol intake.
If diet and lifestyle changes are not effective in adequately lowering cholesterol levels after three to six months, medications may be prescribed. Two common types of cholesterol-lowering medications are “statins” and “fibrates”. Statins are powerful medications and can reduce TC levels by 30-50%. Examples of statin medications include simvastatin (Lipex), and atorvastatin (Lipitor). Fibrates work by lowering LDL and increasing HDL. An example of a fibrate medication is bezafibrate (Bezalip).
Another class of medication that may be used on its own, or to enhance the action of statin medications, are cholesterol-absorption inhibitors. These medications work by preventing cholesterol from being absorbed from the small intestines into the bloodstream. An example of a cholesterol absorption inhibitor available in New Zealand is ezetimibe (Ezetrol).
When taking cholesterol-lowering medications, it is still important to maintain a low saturated fat diet and exercise.
Further information and support
For assessment and treatment of high cholesterol levels see a doctor. For ideas about how to lower high cholesterol levels a doctor or dietician can assist.
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Heart Foundation (2016). Cholesterol (Poster). Auckland: The Heart Foundation of New Zealand. http://assets.heartfoundation.org.nz/shop/heart-healthcare/cholesterol.pdf
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Last Reviewed – December 2016