Cholesterol is a type of fat that circulates in your blood. Too much of it increases your risk of heart disease and stroke.
The condition doesn't have any obvious symptoms so blood tests are required to confirm if a person has high blood cholesterol.
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.
General information and causes
Cholesterol is a white, waxy substance that is circulated in the blood. It is essential for your good health as it helps to build cell walls and is used in the manufacture of some hormones.
However, when there is more cholesterol circulating in the blood than the body needs, it can build up on your artery walls, eventually leading to narrowing and hardening of the arteries. This process is known as atherosclerosis and increases the risk of heart attack, stroke and other cardiovascular diseases. More than half of New Zealanders admitted to hospital with a heart attack have high cholesterol levels.
This risk of a cardiovascular health event increases when high blood cholesterol is accompanied by other risk factors such as high blood pressure and a family history of heart disease.
Your liver produces most of the cholesterol circulating in your blood. A diet high in saturated fat stimulates the liver to produce more cholesterol so the saturated fat content of the food you eat is likely to have a strong influence on your blood cholesterol levels.
A small proportion of your blood cholesterol is derived from dietary cholesterol - i.e. cholesterol that is already present in animal foods you might consume (mainly in dairy products, meat, egg yolks, offal and shellfish).
Other factors that may influence your blood cholesterol levels include:
- Genetic susceptibility to high cholesterol
- Medical conditions such as diabetes, kidney disease and underactive thyroid (hypothyroidism)
- Being overweight or obese
- Physical inactivity
- High stress levels
- Increasing age
- Excessive alcohol intake
“Good” and “bad” cholesterol
There's only one kind of cholesterol but it is carried around the body by different carriers called lipoproteins, notably:
- Low density lipoprotein (LDL)
- High density lipoprotein (HDL)
In simple terms, cholesterol carried by LDLs 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 (i.e. atherosclerosis). If you have high blood cholesterol your goal will be to reduce LDL levels in your blood.
On the other hand, cholesterol carried by HDLs is considered “good” because it carries cholesterol away from the arteries and back to the liver, where it is broken down and passed from the body. Any lifestyle changes or treatment for high blood cholesterol will aim to ensure HDL levels are increased or maintained at healthy levels.
When blood cholesterol tests are done, the level of triglycerides in your blood is 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 done by your family doctor or at a medical clinic. Your doctor will likely assess other risk factors for cardiovascular disease 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:
- LDL-cholesterol – less than 2.0 mmol/L
- HDL-cholesterol – greater than 1.0 mmol/L
- Triglycerides – less than 1.7 mmol/L
- Total cholesterol – less than 4.0 mmol/L
- Total cholesterol/HDL ratio – less than 4.0.
Diet and lifestyle changes
A doctor will look at your overall risk of cardiovascular disease and make recommendations to reduce high blood cholesterol as well as managing other risk factors such as high blood pressure, smoking and being overweight.
Reducing high blood cholesterol levels typically involves decreasing the total cholesterol level by decreasing LDL-cholesterol and triglycerides, while maintaining or increasing HDL-cholesterol levels.
- LDL-cholesterol levels are best decreased by eating less saturated fat (found mainly in animal products such as fatty meat, butter, high-fat milk, cream, and dripping)
- Triglyceride levels are best reduced by eating less sugar-containing foods, limiting alcohol intake, and reducing the intake of total fat
- HDL-cholesterol levels are best increased by exercise, substituting saturated fats with polyunsaturated or monounsaturated fat (e.g. olive-oil based spreads instead of butter), and maintaining a healthy weight.
Heart-healthy dietary changes are summarised in our Heart disease diet page.
Other lifestyle changes should include:
- Exercising regularly (at least 30 minutes of moderate intensity exercise, such as brisk walking, most days of the week)
- Quit smoking
- Maintaining a healthy body weight
- Limiting alcohol intake
- Managing stress.
Heart-healthy exercise suggestions are summarised in our Heart disease exercise page.
If diet and lifestyle changes are not effective in adequately lowering a person's cardiovascular risk related to cholesterol levels after three to six months, medications may be prescribed.
Statins are the most commonly used cholesterol-lowering medication. Statins slow down production of cholesterol in your liver, progressively reducing total cholesterol levels and your risk of a heart attack or stroke.
Other medications may also be prescribed by your doctor in certain circumstances, on their own or in combination with statins.
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 dietitian can assist.
New Zealand Nutrition Foundation (2017). Cholesterol (Web Page). Auckland: NZ Nutrition Foundation. http://www.nutritionfoundation.org.nz/nutrition-facts/nutrition-a-z/cholesterol [Accessed: 05/08/19]
Heart Foundation (Year not stated). Managing high cholesterol (Web Page). Auckland: The National Heart Foundation of New Zealand. https://www.heartfoundation.org.nz/wellbeing/managing-risk/managing-high-cholesterol [Accessed: 05/08/19]
Heart Foundation (2019). Cholesterol (Poster). Auckland: The National Heart Foundation of New Zealand. https://www.heartfoundation.org.nz/shop/heart-healthcare/what-is-cholesterol.pdfMayo Clinic (2019). High cholesterol (Web Page). Rochester, NY: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/symptoms-causes/syc-20350800 [Accessed: 05/08/19]
New Zealand Guidelines Group (2012). New Zealand Primary Care Handbook 2012 (3rd edition). Wellington: New Zealand Guidelines Group. https://www.health.govt.nz/system/files/documents/publications/nz-primary-care-handbook-2012.pdf
BPAC (2017). Prescribing statins to reduce cardiovascular risk. (Web Page). https://bpac.org.nz/2017/statins.aspx [Accessed 21-8-19]
Last Reviewed – August 2019