Cholesterol

Cholesterol is a soft, waxy substance found among the lipids (fats) 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, some hormones and is needed for other functions. But a high level of cholesterol in the blood — hypercholesterolemia — is a major risk factor for coronary heart disease, which leads to heart attack.

Cholesterol and other fats can't dissolve in the blood. They have to be transported to and from the cells by special carriers called lipoproteins. There are several kinds, but the ones to focus on are low-density lipoprotein (LDL) and high-density lipoprotein (HDL).

The concentration of cholesterol in human blood varies rather widely, from a low of less than 200 mg/dL (milligrams per deciliter) to a high of more than 300 mg/dL. It is also found in bile, a source from which, in fact, it gets its name: chole (Greek for bile) + stereos (Greek for solid).

Cholesterol belongs more specifically to a class of compounds known as the steroids. Most steroids are naturally occurring compounds that play critical roles in plant and animal physiology and biochemistry. Other steroids include sex hormones, certain vitamins, and adrenocorticoid hormones. All steroids share a common structural unit, a four-ring structure known as the perhydrocyclopentanophenanthrene ring system or, more simply, the steroid nucleus.



Cholesterol - Properties And Occurrence

Properties and occurrence

Cholesterol crystallizes from an alcoholic solutionas pearly white or pale yellow granules or plates. It is waxy in appearance and has a melting point of 299.3°F (148.5°C) and a boiling point of 680°F (360°C) (with some decomposition). It has a specific gravity of 1.067. Cholesterol is insoluble in water, but slightly soluble in alcohol and somewhat more soluble in ether and chloroform.

Cholesterol occurs in almost all living organisms with the primary exception of microorganisms. Of the cholesterol found in the human body, about 93% occurs in cells and the remaining 7% in the circulatory system. The brain and spinal cord are particularly rich in the compound. About 10% of the former's dry weight is due to cholesterol. An important commercial source of the compound is spinal fluid taken from cattle. Cholesterol is also found in myelin, the material that surrounds nerve strands. Gallstones are nearly pure cholesterol.

The concentration of cholesterol in human blood varies rather widely, from a low of less than 200 mg/dL (milligrams per deciliter) to a high of more than 300 mg/dL. It is also found in bile, a source from which, in fact, it gets its name: chole (Greek for bile) + stereos (Greek for solid).



What is LDL cholesterol?

Low-density lipoprotein is the major cholesterol carrier in the blood. If too much LDL cholesterol circulates in the blood, it can slowly build up in the walls of the arteries feeding the heart and brain. Together with other substances it can form plaque, a thick, hard deposit that can clog those arteries. This condition is known as atherosclerosis. A clot (thrombus) that forms near this plaque can block the blood flow to part of the heart muscle and cause a heart attack. If a clot blocks the blood flow to part of the brain, a stroke results. 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 and your doctor may even set your goal to be less than 70 mg/dL. That's why LDL cholesterol is called "bad" cholesterol. 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. Medical experts think HDL tends to carry cholesterol away from the arteries and back to the liver, where it's passed from the body. Some experts 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. A high level of Lp(a) is an important risk factor for developing atherosclerosis prematurely. How an increased Lp(a) contributes to heart disease isn't clear. The lesions in artery walls contain substances that may interact with Lp(a), leading to the buildup of fatty deposits.

What about cholesterol and diet?

People get cholesterol in two ways. The body — mainly the liver — produces varying amounts, usually about 1,000 milligrams a day. Foods also can contain cholesterol. Foods from animals (especially egg yolks, meat, poultry, shellfish and whole- and reduced-fat milk and dairy products) contain it. Foods from plants (fruits, vegetables, grains, nuts and seeds) don't contain cholesterol.

Typically the body makes all the cholesterol it needs, so people don't need to consume it. Saturated fatty acids are the main culprit in raising blood cholesterol, which increases your risk of heart disease. Trans fats also raise blood cholesterol. But dietary cholesterol also plays a part. The average American man consumes about 337 milligrams of cholesterol a day; the average woman, 217 milligrams.

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. Still, everyone should remember that by keeping their dietary intake of saturated and trans fats low, they can significantly lower their dietary cholesterol intake. Foods high in saturated fat generally contain substantial amounts of dietary cholesterol.

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.



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. Aerobic physical activity raises your heart and breathing rates. Regular moderate-to-vigorous-intensity physical activity such as brisk walking, jogging and swimming also condition your heart and lungs.

Physical inactivity is a major risk factor for heart disease. Even moderate-intensity activities, if done daily, help reduce your risk. Examples are walking for pleasure, gardening, yard work, housework, dancing and prescribed home exercise.

How does tobacco smoke affect cholesterol?

Tobacco smoke is one of the six major risk factors of heart disease that you can change or treat. Smoking lowers HDL cholesterol levels and increases the tendency for blood to clot.

How does alcohol affect cholesterol?

In some studies, moderate use of alcohol is linked with higher HDL cholesterol levels. However, because of other risks, the benefit isn't great enough to recommend drinking alcohol if you don't do so already.

If you drink, do so in moderation. People who consume moderate amounts of alcohol (an average of one to two drinks per day for men and one drink per day for women) have a lower risk of heart disease than nondrinkers. However, increased consumption of alcohol brings other health dangers, such as alcoholism, high blood pressure, obesity, stroke, cancer, suicide, etc. Given these and other risks, the American Heart Association cautions people against increasing their alcohol intake or starting to drink if they don't already do so. Consult your doctor for advice on consuming alcohol in moderation.







Why Do People Worry About High Cholesterol?

When you have too much cholesterol, it can be dangerous to your health. When LDL cholesterol levels are high, cholesterol is deposited on the walls of arteries and forms a hard substance called plaque. Over time, plaque causes the arteries to become narrower, decreasing blood flow and causing a condition called atherosclerosis (pronounced: ah-thuh-ro-skluh-ro-sis), or hardening of the arteries.

When atherosclerosis affects the coronary arteries (the blood vessels that supply the muscles of the heart), the condition is called coronary artery disease, which puts a person at risk for having a heart attack. When atherosclerosis affects the blood vessels that supply the brain, the condition is called cerebral vascular disease, which puts a person at risk of having a stroke. Atherosclerosis may also block blood flow to other vital organs, including the kidneys and intestines. This is why it's so important to start paying attention to cholesterol levels as a teen - you can delay or prevent serious health problems in the future.

What Causes High LDL Cholesterol Levels?

Some of the factors that can lead to high cholesterol are:

· Overweight - Excess weight has been linked with high cholesterol levels.

· Heredity - If cholesterol problems or heart disease run in your family, you are at a higher risk for having problems.

· Diet - Remember the saying "you are what you eat"? Avoid foods that are high in cholesterol, saturated fat, and trans fat, all of which increase cholesterol levels and your risk of developing heart disease.

· Physical activity - Exercise tends to increase HDL levels, which lowers your chance of developing heart disease.

· Age - The risk of high cholesterol increases as you get older.





What Can I Do to Lower My Cholesterol?

Some people who have high cholesterol levels need to be on medication as part of their treatment to lower it. Although most teens won't need to take medication to lower their cholesterol, it's still important to keep cholesterol in check. To see if you have high cholesterol, talk to your doctor, who can test your cholesterol levels by drawing a sample of your blood.



You can't change your genes but there are things you can do now to decrease your risk for heart disease later. Try to eat less saturated fat, limit the amount of trans fat, and limit cholesterol (check food labels if you're not sure how much of these particular foods contain). The American Heart Association recommends that cholesterol intake should be less than 300 milligrams a day, total fat intake should be 30% or less of your total calories, and saturated fat should be 10% or less of the total daily calories you consume. Also, maintain a healthy weight and get moving. Regular aerobic exercise - stuff like biking, walking, and swimming - strengthens your heart, lowers cholesterol, and helps you to lose excess weight. For people who smoke, quitting can help decrease the risk of heart diseaseTop of Form 1

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