By Teresa Doherty
Cholesterol is a waxy fat-like substance that is found in the skin, brain, nerves, blood, liver and bile salts that play a part in fat digestion and detoxification. It is an essential component in the formation of steroid and adrenal corticosteroid hormones, nerve function and for the proper functions of our cells. When excessive cholesterol is present in the blood and especially in an oxidated form, it is one of the contributors to the development and hardening of arteries, know as arteriosclerosis 1. Keeping cholesterol in the proper range is an important step in the prevention of heart attack and stroke.
The Importance of Cholesterol to Cells
Cholesterol plays an essential role in the structure of the cell membrane. In order that cells can perform their function effectively they need to have the correct ratio of phospholipids and cholesterol. Cholesterol provides rigidity, while phospholipids favour fluidity of the cell membrane. The cholesterol content of cell membranes varies over a wide range depending upon the function of the cell. For example, nuclear or mitrochondrial membranes contain as little as 8% cholesterol, whereas muscle fibres that need to be more resistant to deformation contain up to 28% cholesterol2.
How is Cholesterol transported Around the Body?
Cholesterol is transported in the blood on carriers called lipoproteins. The categories of lipoproteins are:
Low Density Lipoprotein (LDL), which carry fats and cholesterol from the liver out to the body cells.
High Density Lipoprotein (HDL) is responsible for returning fat and cholesterol to the liver where it is metabolised and removed.
Triglycerides are the chemical form in which fat exists in our body.
Elevation of oxidised LDL, blood plasma triglyceride and low levels of HDL are associated with increased risk of atherosclerosis3, 4.
Where do we get Cholesterol?
Cholesterol comes from two sources: animal foods in the diet and from the biosynthesis of fat, sugars and proteins in the liver. The cholesterol formed by the liver is vital to those following a vegan diet. An excessive intake of non essential fats and sugar can result in more cholesterol being made by the body5.
How much from the liver?
In the body there is a feedback control mechanism that maintains cholesterol homeostasis. If there is more cholesterol of dietary origin circulating in the blood the liver reduces its biosynthesis. When the diet provides no cholesterol the biosynthesis by the liver takes over.
What Causes High Cholesterol?
In many cases the cause of elevated cholesterol levels are due to dietary and lifestyle factors. Excessive intake of animal produce and inactivity can compromise the body’s ability to regulate cholesterol levels. However this is not the whole story.
It is well established that patients with hyperthyroidism are prone to coronary heart disease due to increased LDL and decreased HDL14.
Familial hypercholesterolemia (FH)
FH is caused by a defect in the receptor protein of the cholesterol carrier in the body. LDL normally circulates in the body for 2.5 days, and subsequently binds to liver cells where it is broken down and removed. When the liver cell takes up the LDL after it has bound to the receptor, it signals the liver to stop making cholesterol and homeostasis is maintained. In FH, the LDL receptor function is reduced or absent and LDL circulates for an average of 4.5 days, resulting in increased levels of LDL cholesterol in the blood15, additionally the liver does not receive the message to stop making cholesterol.
Damage to the LDL receptor
Occurs as a result of
- A diet high in saturated fat decreases the number of receptors, thereby reducing the feedback mechanism16.
Research has shown that some drugs can increase the body’s cholesterol production17. It is not clear to what extent toxins from food and the environment have in negatively affecting the feedback mechanism.
Natural Compounds that can Improve Cholesterol Levels
- Niacin has been shown to achieve very good overall results in reducing LDL cholesterol and triglyceride levels, whilst raising HDL cholesterol levels 18, 19. When using high doses of niacin it is recommended that cholesterol and liver enzyme levels are regularly checked. Niacin can impair blood sugar control; therefore care needs to be taken in cases of diabetes.
- Natural flavonoids found in a wide variety of fruits and vegetables have been shown to reduce the incidence of cardiovascular disease. In particular citrus and palm fruit extracts that contain polymethoxylated flavones, Tangeretin, have been shown to reduce total cholesterol, LDL and triglycerides 20, 21.
- In studies garlic has the ability to lower blood cholesterol 22. When garlic is cooked its active enzyme, allinase is inactivated.
- Good levels of vitamin C have been shown to correspond with low total cholesterol and triglycerides and higher HDL levels23.
- Plant sterols, are a group of phytochemicals that naturally occur in plants. They resemble the chemical structure of cholesterol and carry out a similar function in plants. The human intestine does not absorb sterol efficiently24; therefore a high intake is required to be effective. If enough sterols are consumed they are thought to compete for absorption with cholesterol in the digestive tract, thereby reducing the amount of cholesterol absorbed25.
Taking and Active Approach
Regular exercise has a positive effect upon cholesterol by:
- Increasing the production and action of enzymes that positively alter the rate of cholesterol synthesis 26
- Improving the HDL levels27
- Enhancing the reverse cholesterol transport system27
- Reducing triglycerides rich particles that promote deposits on the artery wall.
HDL cholesterol is generally responsive to endurance exercise and has been shown to improve in a dose-dependent manner. Studies have shown that the length of the exercise training session as well as the amount of exercise completed has an important role in determining HDL change 28. Studies have suggested that an exercise intensity of above 6 METs is needed to improve cholesterol levels 29, 30. Another reported that moderate- intensity training over a 12 week period improved HDL levels31, whilst exercise sessions at a low intensity and for a short duration brought about minimal triglyceride and lipoprotein changes28. It is suggested that for exercise to significantly improve cholesterol levels a high volume of exercise that utilises above 1500kcal or more per week is recommended31.
Resistance exercise has not been shown to have direct benefits upon lipid and lipoprotein changes. However a reduction in body fat and increase in lean body mass as a result of a resistance training program can bring about improvement to LDL28.
Dietary Guidelines to Keeping Cholesterol under Control
The most important approach to lowering high cholesterol is through eating a healthy diet and lifestyle.
- Reduce saturated fats
- Reduce the amount of animal food in the diet.
- Eat a diet rich in plant food, high in fibre and antioxidants
- Take regular amounts of endurance exercise.
- Don’t smoke
- Reduce coffee intake.
- Reduce levels of refined carbohydrates
- Reduce salt consumption
- Eat oily fish and or flaxseed
Cholesterol plays both vital and detrimental roles in our health. The important approach to reducing blood cholesterol levels is through a healthy lifestyle and diet. In addition to these measures there are a number of natural compounds that have been shown to improve cholesterol and triglyceride levels.
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- Ross, E., et al. Effects of Lifestyle Activity vs Structured Aerobic Exercise in Obese Women: A Randomized Trial. The Journal of the American Medical Association. (1999) 281, 335-340.
- Kung, AW., et al. Elevated Serum Lipoprotein(a) in Subclinical Hypothyroidism. Clinical Endocrinology. (1995) 43, 445-449.
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- Roza, JM., et al. Effects of citrus flavonoids and tocotrienols on serum cholesterol levels in hypercholesterolemic subjects. Alternative Therapies. (2007) 13(6) 44-48.
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