What is Cholesterol?
Cholesterol is a soft, waxy substance produced by the body and found naturally in animal foods such as meat, fish and eggs. Cholesterol, a type of lipid (fatty substance), is found in the bloodstream and in all your body's cells. It's an important part of a healthy body because it's used to form cell membranes, make some hormones, synthesize vitamin D, and form bile secretions that aid in digestion. However, a high level of cholesterol in the blood — hypercholesterolemia — is a major risk factor for coronary heart disease, which in turn can lead to a heart attack.
Cholesterol and other fats are unable to dissolve in blood and so are transported to and from cells via the bloodstream by lipoproteins. Lipoproteins are made of fat (lipids) on the inside and proteins on the outside.
There are several kinds of lipoproteins, but two of the most important are low-density lipoprotein (LDL) and high-density lipoprotein (HDL).
What is LDL cholesterol?
Low-density lipoprotein is the primary cholesterol carrying substance in the body. LDL is formed from VLDL (very low density lipoprotein) which is assembled in the liver from cholesterol and apolipoprotiens (protein constituents of lipoproteins) and then circulates through the bloodstream giving up triglycerides until it is converted into LDL. LDL cholesterol is often known as "bad cholesterol." However, it is not necessarily the cholesterol that is bad; it is instead how and where it is being transported, and in what amounts over time.
LDL carries cholesterol from the liver and small intestine to the body's tissues. If too much LDL cholesterol circulates in the blood, it can slowly build up in the walls of the arteries of the heart and brain. Together with fat and other substances it can form "atheromas" or plaques, thick, hard deposits that can clog those arteries. This condition is known as atherosclerosis. Eventually, this fatty tissue can erode the wall of arteries, diminishing their elasticity and interfere with blood flow. Plaques can also rupture, causing debris to migrate downstream within an artery and cause clots to form around the plaque deposits, further interfering with blood flow and posing added danger if they break off and travel to the heart, lungs, or brain. Essentially your risk of coronary artery disease (oxygen-rich blood depravation to the heart), angina (chest pain from oxygen-rich blood depravation to the heart), heart attack (blood supply to a portion of the heart is completely cut off by total blockage of a coronary artery), stroke and circulatory problems increases with too much cholesterol.
A high level of LDL cholesterol (160 mg/dL and above) reflects an increased risk of heart disease. If you have heart disease, your LDL cholesterol should be less than 100 mg/dL. Lower levels of LDL cholesterol reflect a lower risk of heart disease.
What is HDL cholesterol?
About one-third to one-fourth of blood cholesterol is carried by HDL. HDL cholesterol or "good cholesterol" promotes breakdown and removal of cholesterol from the body. Medical experts believe HDL tends to carry cholesterol away from the arteries and back to the liver, where it is then excreted from the body. Some experts also believe HDL removes excess cholesterol from plaques and thus slows their growth. HDL cholesterol is known as "good" cholesterol because a high HDL level seems to protect against heart attack. The opposite is also true: a low HDL level (less than 40 mg/dL in men; less than 50 mg/dL in women) indicates a greater risk. A low HDL cholesterol level also may raise stroke risk.
What is Lp(a) cholesterol?
Lp(a) is a genetic variation of plasma LDL. It is a lipoprotein that resembles LDL in composition with an abnormal protein, termed [a], attached. The concentration of Lp(a) in plasma is genetically determined. The exact function of Lp(a) in the body is unclear; however a high level of Lp(a) is a risk factor for coronary artery disease. Elevated levels are linked to a greater likelihood of atherosclerosis and heart attacks in both men and women and is one of the best predictors of heart attack in young men, blockage of vein grafts following coronary bypass surgery, and blockages in the carotid arteries of the neck. How an increased Lp(a) contributes to heart disease isn't clear. Lp(a) may compete with plasminogen (a substance produced by the body to aid in the breakdown of clots) and thereby interfere with the body's normal clot dissolving mechanism, thus increasing clotting potential and the risk of a heart attack.
How does diet affect cholesterol?
People get cholesterol in two ways. First, the body — mainly the liver — produces varying amounts, usually about 1,000 milligrams a day. Second, foods also can contain cholesterol. Foods from animals (especially egg yolks, meat, poultry, fish, seafood and whole-milk dairy products) contain cholesterol. These foods yield dietary cholesterol. Foods from plants do not contain cholesterol.
Some of the excess dietary cholesterol is removed from the body through the liver. Still, the American Heart Association recommends that you limit your average daily cholesterol intake to less than 300 milligrams. If you have heart disease, limit your daily intake to less than 200 milligrams.
People with severe high blood cholesterol levels may need an even greater reduction. Since cholesterol is in all foods from animal sources, care must be taken to eat no more than six ounces of lean meat, fish and poultry per day and to use fat-free and low-fat dairy products. High-quality proteins from vegetable sources such as beans are good substitutes for animal sources of protein.
Besides direct dietary cholesterol, saturated fatty acids and trans fats are major contributors to increasing blood cholesterol and increasing the risk of heart disease.
Thus, reducing the amount of saturated fat, trans fat and cholesterol you eat is a very important step in reducing your blood cholesterol levels. Also the consumption of polyunsaturated fat helps to reduce cholesterol.
How does physical activity affect cholesterol?
Regular physical activity increases HDL cholesterol in some people. A higher HDL cholesterol is linked with a lower risk of heart disease. Physical activity can also help control weight, diabetes and high blood pressure. Physical activity is any bodily movement, produced by skeletal muscles, that results in energy expenditure. Moderate to intense physical activity, such as brisk walking, jogging and swimming, condition your heart and lungs. Even things like yard work, house work and dancing, if done daily, contribute to a healthier physical lifestyle.
How does smoking affect cholesterol?
Tobacco smoke is a major risk factor of heart disease and stroke. Smoking lowers HDL cholesterol levels, increases triglyceride levels, damages the lining of blood vessels and increases the tendency for blood to clot. People who use smokeless tobacco also have higher cholesterol levels than those of people who don't use tobacco.
How does alcohol affect cholesterol?
In some studies, moderate use of alcohol is linked with higher HDL cholesterol levels. It has been found that ingesting 1-2 drinks of alcohol per day (a "drink" being the equivalent of 1 ½ oz) may increase HDL levels and reduce the risk of heart attack. Men who consume 1-2 drinks a day and women who consume one drink a day have a lower risk of heart disease than nondrinkers. A specific study also found that for postmenopausal women one drink of alcohol a day is sufficient to lower LDL cholesterol and two drinks daily additionally raises the levels of HDL cholesterol. (Reference: Baer, D. J., et al. Moderate alcohol consumption lowers risk factors for cardiovascular disease in postmenopausal women fed a controlled diet. American Journal of Clinical Nursing, 2002, 75, 593-599).
However, because of other risks such as alcoholism, high blood pressure, obesity, stroke, cancer, suicide, etc. the benefit isn't great enough to recommend drinking alcohol if you don't do so already. Consult your doctor for advice on consuming alcohol in moderation.
How does caffeine affect cholesterol?
Most studies involving U.S. style filter-brewed coffee have not found an association between caffeinated or decaffeinated filtered coffee and increased risk of cholesterol-related heart disease. The best evidence to date shows neither caffeinated nor decaffeinated coffee consumption contributes significantly to the risk of heart disease or estimated risk based on serum cholesterol levels.
How does weight affect cholesterol?
Weight affects LDL-cholesterol levels, triglyceride levels and HDL cholesterol levels. Excess weight tends to increase your LDL cholesterol level. If overweight, weight loss may help to lower LDL-cholesterol levels, raise HDL cholesterol levels and help to lower triglycerides.
How does stress affect cholesterol?
Stress over the long term has been shown in several studies to raise blood cholesterol levels. One way that stress may do this is by affecting your habits. For instance, some people tend to consume more foods heavy in saturated fat and cholesterol when under stress. This contributes to higher levels of blood cholesterol.
How does age and sex affect cholesterol?
Before the age of menopause, women usually have total cholesterol levels that are lower than those of men the same age. As women and men get older, their blood cholesterol levels rise until about 60 to 65 years of age. After the age of about 50, women often have higher total cholesterol levels than men of the same age.
Cholesterol and other factors
Heredity also affects your cholesterol levels. Genetics partly determine how much cholesterol your body makes and tendencies for high blood cholesterol may be hereditary. Certain medications and medical conditions can also add to high cholesterol.
When should I start having my cholesterol level checked?
Men aged 35 and older and women aged 45 and older should have their cholesterol checked periodically. Depending on what your cholesterol level is and what other risk factors for heart disease you have (see below), you may need to have it checked more often.
Risk Factors for Heart Disease
• Having already had a heart attack
Related AHA publications:
From The American Academy of Family Physicians: