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What is high cholesterol?

Cholesterol is a type of fat found in all the body’s cells and carried around the body in the bloodstream. It is produced by the liver and most of the cells in the body. It is also found in some foods.

Cholesterol is essential for the body’s functioning as it plays an important role in building cells, producing certain hormones like oestrogen and testosterone, helping the metabolism work, and producing acids needed to help the body digest fat and absorb important nutrients.

High cholesterol

High cholesterol is when there is too much cholesterol in the blood. The excess amounts can build up on the walls of the blood vessels and form plaques that narrow the arteries. This is known as atherosclerosis. Narrowed arteries make it harder for blood to flow to the heart and other organs, increasing the risk of cardiovascular diseases (CVDs) like heart attack and stroke.

Cholesterol travels through the bloodstream and the body in lipoproteins. There are two main types of lipoprotein that carry cholesterol: high-density lipoprotein (HDL) and low-density lipoprotein (LDL).

Good cholesterol: High-density lipoprotein (HDL)

HDL cholesterol is considered the “good” cholesterol, so higher levels of this are actually better. HDL carries excess amounts of the “bad” cholesterol back to the liver, where it is broken down and filtered from the body.

Bad cholesterol: Low-density lipoprotein (LDL)

LDL cholesterol is considered the “bad” cholesterol, as excess amounts can build up on the walls of the arteries, forming atherosclerotic plaques that narrow the arteries and make them hard. This can lead to blockages in the arteries that prevent blood flow to important organs. If this happens in the major blood vessels supplying the heart, you have a heart attack. In the brain, you have a stroke.

What causes high cholesterol?

The risk factors for high cholesterol that can be controlled include the following.

  • Poor diet: What we eat has an impact on cholesterol levels – eating too much food that contains saturated fat and trans fats can lead to unhealthy cholesterol levels. Reducing intake of foods high in unhealthy fat, such as fried and processed foods, can help to manage cholesterol levels.
  • Overweight and obesity: Being an unhealthy weight can increase the risk of high cholesterol as well as other health problems, including other CVD risk factors like high blood pressure. Regular exercise and eating a healthy diet can help manage the risk of being overweight or obese.
  • Smoking: Smoking cigarettes may lower the levels of the “good” HDL cholesterol. Smoking also increases the risk of CVD by damaging the arteries, affecting blood flow through the arteries and making blockages more common. Quitting smoking can almost immediately improve health as well as decrease some of the risk of developing CVD.
  • Inactivity: Exercise helps to boost levels of the “good” HDL cholesterol. Being inactive can increase the risk of high cholesterol levels and other CVD risk factors like high blood pressure. It’s important to make exercise or physical activity a regular part of your day, aiming for at least 30 minutes of moderate-intensity physical activity on most days. However, being active for any amount of time is better than none.
  • Alcohol: Excessive amounts of alcohol can reduce levels of the “good” HDL cholesterol as well as increase other risk factors for CVD. Limiting alcohol intake will help decrease these risks.

Causes of high cholesterol that cannot be controlled

Risk factors that cannot be controlled include the following.

  • Family history: If high cholesterol levels run in your family, you may be at higher risk of high cholesterol and CVD. It’s important to speak to your doctor about your specific situation.
  • Age: While children can have unhealthy cholesterol levels, it becomes much more common in people over 40. With age, the liver becomes less effective at removing the “bad” LDL cholesterol.

Other causes of high cholesterol

  • Medical conditions: Some conditions can cause unhealthy cholesterols levels. These include diabetes, liver or kidney disease, polycystic ovary syndrome and conditions that increase levels of female hormones, such as pregnancy.
  • Medications: Some types of medications taken for other health conditions can also have an impact on cholesterol levels. These include certain medications for high blood pressure, irregular heart rhythms, acne and cancer.

High cholesterol signs and symptoms

High cholesterol generally has no signs and symptoms, so many people are unaware that they even have it. That’s why it’s important for cholesterol levels to be checked through a blood test by a healthcare professional.

For people aged 45 years and over, you can have your cholesterol checked as part of a heart health check with your doctor. These checks usually take around 20 minutes and are covered by Medicare in Australia.

If your results show that your cholesterol levels are not within a healthy range, your doctor may recommend more frequent checks.

You may also be recommended to have more frequent checks if you have a family history of high cholesterol, CVD or other risk factors, such as diabetes or high blood pressure.

High cholesterol levels: what's normal?

A blood test (lipid profile) will measure your total cholesterol levels, LDL cholesterol, HDL cholesterol and triglycerides (another type of fat in the blood).

The safe levels of cholesterol to have in your blood can vary depending on a number of factors.

  • Total cholesterol levels should be lower than 5.5 mmol/L in adults with no other risk factors for CVD.
  • LDL cholesterol levels should be less than 2 mmol/L if you have CVD risk factors or pre-existing CVD or diabetes.
  • HDL cholesterol levels should be kept higher and at a minimum of 1.5 mmol/L. Low HDL cholesterol levels can be a major risk factor for CVD.

Safe levels of cholesterol

Desirable (mmol/L)Borderline (mmol/L)High (mmol/L)
HDL cholesterol>1.5N/AN/A
LDL cholesterol1.7–3.53.6–4.5>4.5
Triglycerides0.5–1.71.8–2.5>2.5
Total3.9–5.55.5–6.5>6.5

How can you lower high cholesterol or prevent it?

Having high cholesterol levels increases the risk of developing CVDs like coronary heart disease, heart attack and stroke. Lowering your levels can help control the risk of these diseases developing. There are several simple ways to help lower high cholesterol, including lifestyle changes like eating or avoiding certain foods, staying active to maintain a healthy weight and quitting smoking. These changes can also help prevent high cholesterol developing in the first place.

  • Avoid foods high in unhealthy saturated and trans fats: These foods include fatty meats, processed foods and meats like sausage, deli-style meats like salami, deep-fried fast food, ice cream, baked goods like cakes, biscuits and pastries, and shack foods like chips and chocolate.
  • Eat foods containing fibre: Foods that are high in dietary fibre, particularly soluble fibre, can reduce the amount of “bad” LDL cholesterol in your blood. Fibre-containing foods include vegetables, fruits, wholegrains, legumes, nuts and seeds.
  • Eats foods containing healthy fats: These foods can increase levels of the “good” HDL cholesterol. Foods with healthy fats include avocado, olives, nuts, seeds and fish.
  • Lead an active lifestyle with regular exercise: Inactivity and sedentary behaviour can increase the risk of high cholesterol, while exercise helps to boost levels of the “good” HDL cholesterol and help to maintain a healthy weight.
  • Quit smoking: Smoking cigarettes may lower the levels of the “good” HDL cholesterol and lead to high cholesterol increasing the agility of the “bad” LDL cholesterol to damage artery cells. Quitting smoking is one of the best things you can do for your cholesterol levels as well as heart and overall health.
  • Limit alcohol intake: Limiting alcohol intake can help decrease high cholesterol and may help lower triglyceride levels. Excessive amounts of alcohol can reduce levels of the “good” HDL cholesterol.

What are the worst foods for high cholesterol?

High cholesterol increases our risk of heart disease, so it’s important to take steps to reduce it. The good news is that simple diet and lifestyle changes, such as avoiding high cholesterol foods, can help stop high cholesterol. Read about the high cholesterol foods to stay away from, including fried foods, fast food, processed meats and baked goods.

How is HRI fighting high cholesterol?

HRI is conducting groundbreaking research from a broad range of angles to understand how atherosclerotic plaque, which consists of cholesterol and other substances, develops through atherosclerosis and to find innovative ways of preventing, detecting and treating the resultant CVD.

Our Thrombosis Group is investigating how atherosclerotic plaque can promote the formation of blood clots, which can lead to heart attack and stroke.

Our Atherosclerosis and Vascular Remodelling Group focuses on identifying and gaining insights from the pathways involved in the build-up of atherosclerotic plaque, which could be used to improve treatments for atherosclerotic plaque.

Our Clinical Research Group is focusing on children and young adults with risk factors for early heart disease such as high levels of cholesterol, and on how to prevent the development of atherosclerosis. Early detection and prevention may save hundreds of thousands of lives from CVD each year.

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