What you need to know about cholesterol

What is cholesterol?

Cholesterol is a soft, waxy, fat-like substance that is found in the cells of all mammals.  It has several functions and is essential for life. 

The term "cholesterol" is used in two different but related ways:

1. When you hear or read about cholesterol in the diet (e.g., "Egg yolks have a lot of cholesterol"), the term refers to the cholesterol molecule. This molecule is found in all animal cells and has several important functions.
2. When you hear or read about cholesterol in the blood (e.g., "My doctor told me that my cholesterol is too high"), the term refers to lipoproteins that can be measured in blood tests. Lipoproteins are packages made of cholesterol molecules, fat and protein. They are assembled in the liver, deposited in the blood and circulate throughout the body. The two main lipoproteins are low-density lipoproteins (LDL) and high-density lipoproteins (HDL).

Cholesterol and cardiovascular disease

Low-density lipoproteins are commonly known as "bad cholesterol." When these lipoproteins circulate in the blood, they interact with the walls of the arteries and create plaques that can lead to atherosclerosis. This narrows arteries and can even block them, which leads to the death of tissue beyond the block that are deprived of oxygen. When this happens in the heart it is called a heart attack (cerebral infarct). When it happens in the brain it is called a stroke (cerebral infarct).

High-density lipoproteins, on the other hand, are commonly known as "good cholesterol." A high level of these particles in the blood is associated with a decreased risk of heart attack and stroke. HDL particles act as scavengers and reduce the risk of cardiovascular disease by "picking up" cholesterol in the arteries and bringing it to the liver to be expelled from the body.

Watch a short video about "good" and "bad" cholesterol.

Cholesterol testing

A physician can request a blood test to measure the level of total cholesterol, HDL and LDL in a person's blood. Measurements are recorded as millimoles per liter of blood (mmol/l). The results provide information about risk for cardiovascular disease. High total cholesterol (above 5.2 mmol/L), low HDL (below 1.0 mmol/L) and high LDL (above 3.4 mmol/L) are generally associated with an increased risk for cardiovascular disease. 

The ratio of HDL to total cholesterol is a useful calculation that can also identify risk. A lower ratio indicates a greater proportion of good cholesterol, which translates to a reduced risk for cardiovascular disease. The ratio should be below 5; ideally, it should be below 3.5.

If a physician identifies that a person is at increased risk for disease related to high cholesterol, they will likely recommend lifestyle measures (see below) or prescribe medications to bring cholesterol levels into a desirable range. Lifestyle measures are preferred since medications have side-effects. Also, the lifestyle measures offer many other benefits beyond their impact on cholesterol. However, for some with a genetic propensity for elevated cholesterol, lifestyle measures may not be sufficient to reduce risk and medications may need to be added to the treatment.

Sources of cholesterol

Cholesterol molecules can be manufactured by the body or they can come from the food we eat. Up to 80% of the body’s cholesterol is made by the liver and is influenced by genetic factors. Therefore, high cholesterol can "run in the family" because some people are genetically inclined to produce more of it.

The remainder of the body’s cholesterol is obtained through the foods we eat. Cholesterol is found only in animal products;  plant sources of food contain no cholesterol. Foods high in cholesterol include egg yolks, organ meats (e.g., liver), fatty meats, shrimp and whole milk dairy products.

General cholesterol content of selected foods

Lifestyle measures to reduce your risk of cardiovascular disease

The link between blood cholesterol levels and the risk for cardiovascular disease has been firmly established. Research has identified several lifestyle factors that contribute to increased risk. Engaging in positive health behaviours can prevent high cholesterol or it can reduce cholesterol levels in those for whom it is elevated.

Below are recommendations for which there is consistent scientific evidence of effectiveness for reducing cholesterol. Many of these factors are related to diet. Following the advice in Canada's Food Guide will ensure that you meet the nutrition based recommendations below.

Strategies to decrease LDL (“bad" cholesterol)

• Decrease saturated fats: Saturated fats in the diet increase LDL levels. Experts recommend keeping saturated fats to 7% or less of daily calories. For the average Canadian — who needs about 2,000 calories a day — this translates to just over 15 grams of saturated fats. Saturated fats are found predominantly in junk foods, desserts and animal products, especially red meat and dairy products such as milk, cheese, cream, ice cream and butter. Some ways to decrease saturated fat include:
  • consult food labels for saturated fat content
  • choose lower fat dairy products (reduced fat cheese, skim or 1% milk, low-fat or fat-free sour cream etc.)
  • reduce meat consumption; when you do eat meat choose leaner cuts and remove the visible fat or the skin
  • use non-hydrogenated margarines rather than butter
  • avoid or limit junk food (e.g., chips) and fast food (e.g., McDonald’s)
• Avoid trans fats: Trans fats in the diet also increase LDL levels. Experts recommend that we consume no more than 1% of our total daily calories as trans fat. For the average Canadian this means no more than 2.5 grams a day. Trans fats are found in hydrogenated oils and products made with them or fried in them. To reduce trans fats in your diet avoid or limit fried foods, commercial baked goods (e.g., pies, cakes, cookies) and other foods made with hydrogenated or partially hydrogenated oils. Trans fat content of packaged foods is indicated on the food label, so be sure to check your Nutrition Facts panel.
• Consume a diet rich in fibre: Fibre binds to compounds that make LDLs and removes them from the blood. As the levels of these building blocks drop, so does the level of LDL in the blood. Dietary fibre is only found in plant products. Aim to get 10 to 25 grams of soluble fibre per day from food. Beans, oats, barley and some fruit and vegetables are good sources of soluble fibre. Fibre supplements don’t appear to offer the same cardiovascular risk-reducing benefits as dietary fibre.
• Achieve and maintain a healthy weight: Being overweight or obese increases a person's risk of cardiovascular disease, partly by modifying HDL and LDL levels. Research has identified that overweight or obese people who lose 5  to 10% of their body weight can see a 15% decrease in LDL and an 8-10% increase in HDL. Weight loss also has a positive effect on triglycerides.

Research has identified other strategies that can reduce LDL, but they are impractical and the impact on cardiovascular disease is not as great as the strategies outlined above. They include increasing stanols and sterols in the diet (you need to eat fortified foods to get enough) and eating 30 to 50 grams of soy protein each day.

Strategies to increase HDL ("good" cholesterol)

• Engage in regular physical activity: Engaging in regular exercise is associated with increases in HDL, but the impact is slight.  None-the-less, engaging in 150 minutes of moderate- to vigorous-intensity physical activity per week is clearly associated with a significant decrease in the risk of cardiovascular disease through pathways other than a modification of lipoproteins.
• Eat foods rich in Omega-3 fatty acids: Omega-3 fatty acids are known as essential fatty acids because the body cannot make them so they need to come from the diet. They are found in marine food sources — especially fatty fish — as well as in some plant foods such walnuts and flaxseeds. Research has identified that a diet rich in marine sources of omega-3s (known as DHA and EPA) is associated with a lower risk for heart attack and stroke, possibly through the effect of increased HDL. Plant sources of omega-3s (known as ALA) don’t appear to have the same benefit. To increase the amount of heart-protective omega-3s in the diet, consume fatty fish such as salmon, tuna, sardines, herring, mackerel and trout. It is recommended to eat at least two servings of fish a week. You can also get omega-3s from fish oil supplements. Getting at least one gram combined of DHA and EPA per day appears to be related to reduced risk.
• Consume alcohol in moderation: Results of many studies indicate that moderate alcohol consumption improves HDL cholesterol levels and reduces the risk of cardiovascular disease. Moderate consumption is one or two standard drinks a day for men or one standard drink a day for women. A standard drink is 12 oz beer (335 mL), 5 oz wine (140 mL) or 1.5 oz liquor. If you don’t drink alcohol, don’t start just for your cholesterol as there are other lifestyle strategies that have a greater impact.