Cholesterol is a fat-like substance produced by the body. Elevated blood levels of cholesterol or triglycerides (a related type of fat or lipid) is an important risk factor for coronary heart disease. This is especially true for people who also have other risk factors for heart disease. Cholesterol is diagnosed with a blood test. People with high cholesterol are usually treated with a combination of medications and lifestyle changes. Treating high cholesterol significantly reduces your risk of heart disease and stroke.
What Is Cholesterol?
Cholesterol is produced by the body. It is used to produce of certain hormones and is a structural component of cell membranes.
Cholesterol is also found in many foods. Blood levels are affected by genetic factors, age, sex and lifestyle factors, especially diet.
Cholesterol and triglycerides are carried in the bloodstream by particles called lipoproteins. Low-density lipoproteins (LDL, sometimes called “bad” cholesterol) carry most of the cholesterol in the blood. Too much LDL can lead to a buildup of cholesterol-rich plaques in the walls of your arteries, a process called atherosclerosis. This buildup of plaque causes your arteries to narrow which makes it harder for blood to flow through them. High blood levels of triglycerides also contribute to an increase in heart disease risk.
Another type of lipoprotein, high-density lipoprotein (HDL, or “good” cholesterol), carries cholesterol from other parts of the body to the liver, where it is broken down and eliminated. Low levels of HDL are associated with greater risk for heart disease.
Narrowing of the arteries of the heart leads to coronary artery disease, angina, and heart attack. Cardiovascular disease (CVD) includes coronary artery disease, peripheral vascular diseases and carotid artery disease. CVD begins with excess cholesterol being deposited in artery walls (atherosclerosis) which leads to inflammation and reduced blood flow. This can cause angina and pain in the legs and arms (claudication). Similarly, atherosclerosis of the carotid arteries (which lead to the brain) can lead to stroke. When a cholesterol-rich plaque ruptures, the most serious consequences include heart attack and stroke.
Blood Cholesterol: "Good" and "Bad"
Most cholesterol is carried by LDL cholesterol. Excess LDL leads to cholesterol being deposited in the walls of arteries. On the other hand, HDL cholesterol plays an important role in picking up or removing cholesterol from the walls of the arteries and taking it to the liver for excretion. Low levels of HDL are associated with increased heart disease risk. Optimal levels of HDL are above 1.3 mmol/L. Contrary to previous scientific opinion, very high levels of HDL do not provide additional protection. Because of this, the cholesterol-to-HDL ratio is no longer used to assess risk.
Blood levels of cholesterol and triglycerides are determined, in part, by hereditary (genetic) factors. Levels of LDL also increase naturally with age.
Triglycerides are produced in the liver from the fat, carbohydrates, and alcohol in your diet. They are also produced when fatty acids from fat stores in your body return to the liver. High triglyceride levels are often associated with low levels of HDL and are another risk factor for heart disease. Very high blood triglycerides (chylomicronemia) can cause inflammation of the pancreas (pancreatitis).
High blood levels of a cholesterol-carrying particle called lipoprotein(a), or Lp(a), promote the development of cholesterol deposits in arteries (atherosclerosis) and interfere with the breakdown of blood clots (thrombolysis). Lp(a) levels > 25 mg/dL (>250 mg/L) are associated with a significant increase in the risk of heart disease and stroke, and the risk increases proportionally to blood levels of Lp(a). Lp(a) measurement can help determine whether or not cholesterol-lowering medication is necessary.
The inflammatory marker C-reactive protein (CRP) is associated with heart disease risk. CRP can be used to help assess the risk of CVD apparently healthy men and women who have no symptoms. In several recent studies, the rates of coronary events increased significantly with higher levels of C-reactive protein and patients with high levels of CRP benefit from statin therapy. An optimal CRP level is < 1.0 mg/L; and levels above 3.0 mg/L indicate higher risk for heart disease and stroke.
Diabetes is a leading cause of death by disease in the Canadian population. People with diabetes have a three to five fold higher risk for heart disease. There are three types of diabetes:
- Type 1 diabetes: Seen in about 10% of people with diabetes and most commonly in children, type 1 diabetes occurs when the pancreas has been damaged by an immune response, sometimes related to a viral infection. This type of diabetes requires insulin treatment.
- Type 2 diabetes: Affecting 90% of people with diabetes, type 2 diabetes occurs when fat, muscle, and other cells in the body become resistant to the effects of insulin and the pancreas does not produce enough insulin to compensate. This type of diabetes often responds well to weight loss and exercise.
- Gestational diabetes: This form of diabetes occurs in 2 to 4% of women during pregnancy. Gestational diabetes is a risk factor for type 2 diabetes later in life.
An important way to assess diabetes is with a test of glycated haemoglobin (HbA1c). This test provides an overall picture of your average blood sugar levels over the past several weeks. Diabetes is defined as HbA1c of 6.5% or higher. Pre-diabetes is defined as an HbA1c between 6.0 and 6.5%. Most people with type 2 diabetes have two metabolic abnormalities that raise their fasting blood glucose: insulin resistance and poor production of insulin by the pancreas. Treatment of type 2 diabetes consists of weight loss, exercise, and medications to control blood sugar. Since CVD risk is elevated, most patients with diabetes also require statin treatment to lower LDL levels to below 2.0 mmol/L.
Risk factors that can be altered or managed include:
- High levels of saturated fat, trans fat, and cholesterol in the diet
- Being overweight
- Lack of exercise
- High blood pressure
Many people with cholesterol problems are not aware that they have the condition and are at risk for heart disease.
A blood test called Cholesterol Profile is used to measure cholesterol levels. Depending on other cardiovascular risk factors such as diabetes or smoking, the optimal levels are determined on an individual basis.
The table below lists the ideal cholesterol profile:
|Total Cholesterol mmol/L||< 4.0|
|Triglycerides mmol/L||< 1.8|
|LDL-C mmol/L||< 2.0|
Non-HDL-C mmol/L(Tot Chol – HDL-C)
|HDL-C mmol/L||> 1.0 (male); > 1.3 (female)|
Treatment includes lifestyle change and may require medication. This will depend on your other risk factors for heart disease, including smoking, high blood pressure, and family history of heart disease.
Important lifestyle changes for lowering cholesterol include:
- Eating a healthy diet high in fibre and polyunsaturated fats; but low in saturated fat, trans fat, cholesterol and refined carbohydrates
- Losing weight
- Increasing exercise
- Quitting smoking
- Managing diabetes
Cholesterol-lowering medications are required for many patients in addition to maintaining a healthy lifestyle. For most people, statins are the first line of treatment. They lower the production of cholesterol in the liver, reducing LDL cholesterol and triglyceride levels.
Benefits of Lowering LDL-Cholesterol
Clinical trials clearly show that lowering LDL and increasing HDL levels in the blood reduces the risk of major coronary events in patients, whether or not they have clinically evident coronary heart disease or high cholesterol. Research has shown that statin treatment is an effective way to reduce the risk of a major coronary event, as well as the incidence of stroke and total mortality.
Reducing LDL levels is associated with slower progression of mild and moderate blockages in coronary arteries, as well as reduction of moderate to severe blockages. Reducing LDL and/or increasing HDL levels makes plaques in the arteries more stable and less likely to rupture. This decreases the risk for heart attack.
This table summarizes the evidence supporting the use of statin therapy to reduce the risk of heart attack and stroke.
All patients who have evidence of cardiovascular disease (atherosclerosis in any part of the vascular system) or diabetes should be treated with a statin according to the Canadian Cardiovascular Society Guidelines. Statins are safe and effective medications for lowering cholesterol. Significant muscle or liver side effects are uncommon. Some patients may need a second medication, such as ezetimibe, which reduces cholesterol absorption from the intestine.
Statins: Statins are a type of medication used to treat high levels of LDL-cholesterol. Examples of statins you might be prescribed include rosuvastatin (Crestor®), atorvastatin (Lipitor®), fluvastatin (Lescol®), lovastatin (Mevacor®), pravastatin (Pravachol®), and simvastatin (Zocor®).
Ezetimibe: Ezetimibe (Ezetrol®) inhibits cholesterol absorption and can lower LDL-C by 15 to 20%.
Resins: Resins are used to lower LDL-cholesterol and are often used in combination therapy. These include cholestyramine (Olestyr or Questran®) and colesevelam (Lodalis®).
Fibrates: Fibrates are used to treat high levels of blood triglycerides with or without high levels of LDL-cholesterol and to treat low levels of HDL-cholesterol. These include bezafibrate (Bezalip®), fenofibrate (Lipidil).
Niacin: Niacin is sometimes used to treat elevated triglycerides and cholesterol. Niacin is a B vitamin.
In summary, statins reduce cholesterol production by the liver and lower cholesterol by up to 60% and triglycerides by up to 40%. Ezetimibe reduces cholesterol reabsorption from the intestine and can lower cholesterol by 15 to 20%. Fibrates are sometimes used for patients with very high triglycerides as an add-on to statin therapy.
Elevated triglycerides are a risk factor for coronary heart disease, particularly when HDL concentrations are low or when LDL is high. Patients who have a fasting triglyceride level above 6.0 mmol/L are also at risk of pancreatitis, a condition in which the pancreas becomes inflamed. Treatment of high triglyceride levels requires management of blood sugar levels for people with diabetes and avoidance of alcohol, oral estrogen, and retinoids. The most potent statins can lower triglycerides by as much as 40%. Niacin, a B vitamin, lowers triglycerides by 30 to 40%, but its use may be limited by side effects and increased insulin resistance. Fibrates lower triglycerides by a similar amount but can affect kidney function.
Fish Oil: Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), available in the form of salmon oil capsules (1,000 mg three times daily) or krill oil (500 mg two times daily), can be a useful dietary supplement to help lower triglycerides.
Soluble Fibre: Psyllium (Metamucil®), hemp, flaxseed, oat bran, guar gum, and pectin help to lower LDL-cholesterol.
Soy Protein: Replacement of animal protein with soy-based protein can also reduce help LDL-cholesterol levels.
Many risk factors for developing high cholesterol can be reduced with the same lifestyle choices that are used to lower high levels.