Cholesterol & Heart Disease
Cholesterol is a fatty wax-like substance. It is not fat but is contained in many fatty foods; especially the fat in meat, eggs and dairy products although other sources do exists. Cholesterol is manufactured in the body as well. It is a necessary component of many normal structures in the body. Unfortunately, many scientific studies have shown that as blood cholesterol levels get higher, so does the risk for heart attack.
The amount of cholesterol circulating in the blood is what is measured with a “cholesterol blood test”. This measures the cholesterol “manufactured” in the body as well as the cholesterol absorbed from food in the diet. The total cholesterol is actually a measure of cholesterol contained within several different types of particles, called “lipoproteins” that carry cholesterol. These different lipoproteins carry cholesterol in the circulation as it cycles through the body. These particles carry cholesterol from the liver (where cholesterol is made) and from the gut (where cholesterol is absorbed from food) to the tissues (where it is used) and back to the liver (where it is removed). Each particle has a specific activity in the cholesterol cycle. Although this is a complex system, in general, LDL (low density lipoprotein), often called “bad cholesterol” is the particle most associated with the development of atherosclerosis and HDL (high density lipoprotein) is the particle that helps “clear cholesterol” from the blood carrying it to the liver for removal. HDL is commonly considered “good cholesterol” since the higher the level of HDL, the lower the risk of developing atherosclerosis related disease. There are other particles that also carry cholesterol. These are also usually measured during a blood test, do contribute to the “total cholesterol” measured and do increase the risk of atherosclerosis to varying degrees. Currently, however, the recommendations for treatment focus on lowering the level of LDL since it seems to be most responsible for the bad effects seen with increased cholesterol. Raising HDL levels, on the other hand, is a goal of treatment since it “removes” cholesterol and lowers the risk of heart and vascular disease. Unfortunately, this is more difficult to accomplish although it is an area of active research.
How Does Cholesterol Cause Atherosclerosis
Exactly how cholesterol leads to atherosclerosis is complex, not fully understood and an area of active research. In simple terms, cholesterol is carried by lipoproteins in the blood and then transferred to and taken up by the blood vessel wall. There, through a series of interactions with the cells in the blood vessel lining and wall, as well as blood cells (particularly special white blood cells) cholesterol is deposited as atherosclerosis. The likelihood of developing this harmful deposition increases with higher cholesterol levels in the blood as well as other “risk factors” such as smoking, diabetes and high blood pressure. Initially, this is primarily inside the wall of the blood vessel and does not restrict blood flow. Studies have shown these early stages begin occurring in individuals as young as teenagers. This deposition is called plaque. With time, however, these deposits progress and begin to narrow the blood vessel, restricting flow. As the plaque extends into the blood vessel channel (lumen) it is often constructed of a firmer “cap” that covers a core of soft “gooshy” fatty material. This type of plaque is thought to be more likely to cause heart attacks since it is considered “unstable” and often ruptures which can result in the formation of blood clots inside the blood vessel. Some plaques may be more organized and solid. Many plaques also contain calcium deposits that make the blood vessels hard and stiff. Current research suggests that much of this process may be associated with or even caused by inflammation through a complex interaction of all these factors. Much research is being devoted to better understanding this whole process. Hopefully this will lead to better treatments and prevention efforts.
How Low Should Cholesterol Go With Treatment?
An individual’s desirable level of cholesterol, as stated above, is dependent on their global risk. In general, those at the highest risk need aggressive management. For instance, in patients that have had a heart attack, especially with other risk factors such as diabetes, a desirable level of LDL is less than 70 mg/dl. Other individuals that do not have established cardiac or vascular disease but are being treated to prevent such events may have a desirable LDL level of less than 130 mg/dl. What determines each individual’s desirable level is too lengthy to describe in detail here but can be determined by your physician after a thorough evaluation. The various treatment options and plans can then be discussed with that individual.
Although all adults, young and old, should be aware of their cholesterol levels not everyone needs treatment with medication. Treatment starts with an assessment, by your physician, of your global risk. This should include an evaluation for the presence of all cardiovascular risk factors, not just cholesterol. In some individuals it may also be desirable to do various “imaging tests” looking for evidence of developing atherosclerosis. New blood tests, such as those checking for inflammation (hs-CRP) may also be recommended. Once your desirable level of cholesterol has been determined, treatment may be recommended. All individuals should strive for a healthy lifestyle; this should include a diet low in saturated fats and cholesterol along with the recommended amounts of poly and mono-unsaturated fats which can improve cholesterol levels. Additionally, adequate fiber in the form of vegetables, fruits and whole grain products is helpful. Weight loss in those overweight is essential. Exercise is recommended for everyone. Smoking and tobacco products must be discontinued. Most patients, particularly those at high risk, in whom cholesterol lowering is recommended, will require medications to achieve their desirable cholesterol level.
Extensive research has confirmed the effectiveness and safety of cholesterol lowering with medication, in particular the statins, in the prevention of heart attack, stroke and dying of heart disease. Concerns about side-effects are valid but are rarely a reason to not treat cholesterol to the desired level. Your physician can discuss this with you. The commonly used medications are:
1. Statins: Examples are Lipitor®, Zocor®, Crestor® and Pravachol®. These medications stop the “manufacturing” of cholesterol by the body.
2. Fibrates: Examples include gemfibrozil and Tricor®. These medications are used primarily to lower triglycerides and do so by increasing the removal of these particles from the circulation. They do have some effect on LDL lowering and can increase HDL slightly
3. Ezetimibe (Zetia®): This medication works by blocking the absorption of cholesterol contained in the diet.
4. Niacin: Examples include Niaspan®. This medication may work through several mechanisms to both decrease the manufacturing and increase the removal of cholesterol containing particles.
5. Bile acid sequestrants: Examples include Welchol®. These medications decrease the absorption of cholesterol from the intestine.
What Are Tryglycerides?
Triglycerides are the chemical form in which fats are circulated and stored in the body. High triglycerides have also been linked to the development of heart disease. Many conditions can increase the triglyceride levels, including genetic conditions, but high triglycerides tend to be the greatest problem in those individuals that are overweight and in those with diabetes. Triglycerides also are elevated shortly after eating since they are how the body transports and stores the calories that are not “burned”. This includes both fats and carbohydrates since most excess carbohydrate calories are “transformed” to fat for storage. The recommended blood level of triglycerides on a fasting blood test is less than 150 mg/dl. There are medications that can lower triglyceride levels, particularly the fibrates. Fish oil supplements are often recommended. Triglyceride levels can also be reduced with weight loss, exercise, dietary changes (particularly low saturated fat and lower carbohydrate with an emphasis on complex carbohydrates), and avoidance of alcohol, among others.
What Determines Cholesterol Levels?
Many factors determine an individual’s cholesterol level. Food high in saturated fats and cholesterol (primarily animal fats, eggs and dairy products) can increase cholesterol levels. Being overweight or obese can increase and alter cholesterol levels and, in addition to increasing LDL, seems to be particularly associated with higher levels of triglycerides (a type of circulating fat that also increases the chance of developing atherosclerosis) and lower levels of HDL. Inactivity is associated with higher levels of cholesterol while exercise can help increase the level of the good cholesterol, HDL. Individuals can be prone to high cholesterol due to genetic factors, some well defined and hereditary in nature. Certain medications can raise cholesterol such as steroids and hormones. Other diseases such as thyroid disease and diabetes can affect cholesterol levels. There are many other potential causes and factors of high cholesterol and part of the evaluation should be to determine if any of these are present.
Why is High Cholesterol Bad?
There has been extensive research done over decades that has shown a strong association between cholesterol and diseases such as heart attack and stroke. Essentially, the higher the cholesterol, particularly LDL, the higher the risk of heart attack or dying of heart disease. A low HDL has also been shown to have a similar association while high HDL levels have been shown to be “protective”. What is more important to understand is that there is no “safe” or “normal” level of cholesterol; the higher the level of cholesterol, the higher the risk. Additionally, if other atherosclerotic risk factors are present, such as diabetes, the greater the risk for that individual. In other words, what is a “desirable” level of cholesterol depends on many factors, not just the cholesterol level alone. The “total” or “global” risk needs to be determined and treatment is individualized based on the global risk. Your physician can determine what the desirable level of cholesterol is for you as an individual.