High blood cholesterol levels

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 does not 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 certain hormones.

However, when there is more cholesterol circulating in the blood than the body needs, it can build up on the inside surface of your artery walls (cholesterol plaque), 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; hence, 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, which is 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
• Smoking.

High blood cholesterol levels are known medically as hypercholesterolaemia or hyperlipidaemia.

“Good” and “bad” cholesterol

There is 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 (LDL-C) is considered “bad” because when there is 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-C levels in your blood.

On the other hand, cholesterol carried by HDLs (HDL-C) 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-C 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-C 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-C – less than 2.0 mmol/L
• HDL-C – greater than 1.0 mmol/L
• Triglycerides – less than 1.7 mmol/L
• Total cholesterol (TC) – less than 4.0 mmol/L
• TC/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 TC level by decreasing LDL-C and triglycerides, while maintaining or increasing HDL-C levels.

• LDL-C 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-C 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 beneficial lifestyle changes should include:

• Exercising regularly (at least 30 minutes of moderate intensity exercise, such as brisk walking, most days of the week)
• Quitting smoking
• Maintaining a healthy body weight
• Limiting alcohol intake
• Managing stress.

Heart-healthy exercise suggestions are summarised in our Heart disease exercise page.

Medications

If diet and lifestyle changes are not effective in adequately lowering a person's cardiovascular risk related to high 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 cholesterol levels and your risk of a heart attack or stroke. Dietary improvements lower blood cholesterol by a maximum of 20 per cent so some patients will require treatment with statins despite having an excellent diet if their overall cardiovascular disease risk is high.

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.

Our Heart disease diet and Heart disease exercise pages provide practical ideas and ways to get started with healthier lifestyles in general, including cholesterol reduction.

References

Cleveland Clinic (2022). Cholesterol and nutrition. Cleveland, OH: Cleveland Clinic. https://my.clevelandclinic.org/health/articles/16867-cholesterol--nutrition-tlc#:~:text=The%20cholesterol%20you%20gain%20from,to%20rise%20higher%20than%20normal. [Accessed: 16/12/22]

New Zealand Nutrition Foundation (2017). Cholesterol (Web Page). Auckland: NZ Nutrition Foundation. https://nutritionfoundation.org.nz/cholesterol/ [Accessed: 04/11/22]

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: 04/11/22]

Heart Foundation (2019). Cholesterol (Pamphlet). Auckland: The National Heart Foundation of New Zealand. https://www.heartfoundation.org.nz/resources/cholesterol-a5-pamphlet

Mayo Clinic (2021). High cholesterol (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/symptoms-causes/syc-20350800 [Accessed: 04/11/22]

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 (2021). Prescribing statins to reduce cardiovascular risk. (Web Page). https://bpac.org.nz/2021/statins.aspx [Accessed: 04/11/22]

Last Reviewed: November 2022