High blood cholesterol levels are a significant risk factor for heart disease and stroke. Diets that include food low in saturated fats and dietary cholesterol can reduce “bad” cholesterol (LDL) levels and increase “good” cholesterol (HDL) levels.
General information and causes
Cholesterol is a white, waxy substance that is circulated in the blood. High blood cholesterol levels are known medically as hypercholesterolaemia or hyperlipidaemia.
Cholesterol is essential for life. It helps to build cell walls and is used in the manufacture of some hormones. The liver produces approximately 75% of the cholesterol circulating in the blood, while the remaining 25% is derived from the food we eat.
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.
High levels of cholesterol in the blood may be caused by eating a diet too high in saturated fat and/or by having a genetic susceptibility to high cholesterol (familial hypercholesterolaemia). Cholesterol levels can also be influenced by medical conditions such as diabetes and liver or thyroid disorders. Being overweight, physical inactivity and high stress levels can also lead to high blood cholesterol levels.
Dietary cholesterol is present in animal foods - mainly in dairy products, meat, egg yolks and offal - and shellfish. It is not present in plant foods. Eating a diet high in saturated fat stimulates the liver to produce more cholesterol. Both cholesterol-containing and non cholesterol-containing foods can have high levels of saturated fat. Therefore the saturated fat content of food, as well as the cholesterol content of the food, can influence blood cholesterol levels.
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 levels. It is estimated that 90% of adult New Zealanders would benefit by lowering their cholesterol levels.
Types of cholesterol
Cholesterol is carried around the body on special proteins called lipoproteins. There are different types of lipoproteins.
Low density lipoprotein (LDL)
High density lipoprotein (HDL)
LDLs start off as VLDLs (very low density lipoproteins) which transport cholesterol to various parts of the body. After the VLDLs drop off their cholesterol load they turn into LDLs which then carry any leftover cholesterol around the body. When there is too much LDL cholesterol circulating in the blood it can deposit onto the lining of artery walls. For this reason LDL is often referred to as "bad" cholesterol.
HDL cholesterol removes deposits of LDL cholesterol from the artery walls and returns it to the liver where they are broken down and eliminated from the body. For this reason HDL cholesterol is considered to be protective against heart disease and is often referred to as "good" cholesterol.
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, and are also a member of the lipid family. 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. These tests give more accurate results than non-fasting tests.
Acceptable blood cholesterol levels as recommended by the National Heart Foundation of New Zealand are:
- Total cholesterol (TC) - 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 severe hypercholesterolaemia, cholesterol may deposit in other parts of the body such as the upper eyelids (xanthelasma) and at 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.
Treatment for high cholesterol
Treatment aims to decrease the total cholesterol level by decreasing LDL cholesterol levels and increasing HDL cholesterol levels. Initially diet and lifestyle changes may be tried.
Dietary changes 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, root vegetables (kumara, potatoes) instead of fat
- See our healthy heart diet
Lifestyle changes include:
LDL cholesterol levels are best decreased by reducing the intake of saturated fat, while HDL cholesterol levels are best increased by regular exercise (at least 30 minutes duration three times per week), substituting saturated / polyunsaturated fats with 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.
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 total cholesterol 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 it's 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.
Tips for lowering cholesterol
- Set realistic goals and make changes one at a time
- Keep a food diary in order to become more aware of food habits and note areas where changes are required
- Get the support of family and friends
- Change cooking methods to avoid adding fat. Steam, microwave, poach, grill or bake food rather than fry or roast. Use non-stick sprays on cookware rather than oil
- Remove the skin from poultry and trim fat off meat before cooking
- Eat more fish and chicken instead of red meat
- Polyunsaturated and monounsaturated fats should be used in place of saturated fats (eg: olive oil instead of butter). Be wary of vegetable products that are high in saturated fat or transfatty acids, such as hydrogenated vegetable oil and coconut cream
- Avoid prepared food, snacks and meals unless total and type of fat content are known
- Restrict eggs to two or three a week. Use only the egg white instead of the whole egg in cooking
- Try lemon juice, vinegar, or low-fat dressing instead of oily dressings or mayonnaise
- Choose low fat dairy products eg: cottage cheese, skim milk, low-fat yoghurt, instead of higher fat dairy products
- Eat plenty of fresh fruit and vegetables as these are high in fibre and contain no cholesterol and very little or no fat
- Don't smoke
- Limit alcohol intake.
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 dietitian can assist. The National Heart Foundation of New Zealand can also assist with information, support and resources such as low fat cook books. Their contact details are:
National Heart Foundation (National Office)
Box 17 160
Ph: (09) 571 9191
National Heart Foundation of Australia (2012) Cholesterol, triglycerides and coronary heart disease.
New Zealand Nutrition Foundation (2012) Cholesterol. www.nutritionfoundation.org.nz/nutrition-facts/nutrition-a-z/cholesterol
The Heart Foundation of New Zealand (2012) High Cholesterol. www.heartfoundation.org.nz/know-the-facts/conditions/cholesterol
The Heart Foundation of New Zealand (2009) Cholesterol Pamphlet
Last Reviewed – 30 November 2012