All you wished you knew about Cholesterol... CSS topic of General Science.

Cholesterol is a waxy, fat-like compound that belongs to a class of molecules called steroids. It's found in many foods, in your bloodstream and in all your body's cells. If you had a handful of cholesterol, it might feel like a soft, melted candle. Cholesterol is essential for:

• Formation and maintenance of cell membranes (helps the cell to resist changes in temperature and protects and insulates nerve fibers)
• Formation of sex hormones (progesterone, testosterone, estradiol, cortisol)
• Production of bile salts, which help to digest food
• Conversion into vitamin D in the skin when exposed to sunlight.

                                      

Blood Cholesterol vs. Dietary Cholesterol

 About 85 percent of your blood cholesterol level isendogenous, which means it is produced by your body.

The other 15 percent or so comes from an external source -- your diet. Your dietary cholesterol originates from meat, poultry, fish, seafood and dairy products. It's possible for some people to eat foods high in cholesterol and still have low blood cholesterol levels. Likewise, it's possible to eat foods low in cholesterol and have a high blood cholesterol level.

why is there so much talk about cholesterol in our diet? 

because the level of cholesterol already present in your blood can be increased by high consumption of cholesterol and saturated fat in your diet. This increase in dietary cholesterol has been associated with atherosclerosis, the build-up of plaques that can narrow or block blood vessels. (Think about what happens to your kitchen drain pipes when you pour chicken fat down the sink.) If the coronary arteries of the heart become blocked, a heart attack can occur. The blocked artery can also develop rough edges. This can cause plaques to break off and travel, obstructing blood vessels elsewhere in the body. A blocked blood vessel in the brain can trigger a stroke.

The American Heart Association recommends that we limit our average daily cholesterol intake to less than 300 milligrams. Obviously, people with high levels of cholesterol in the blood should take in even less.

Good and Bad Cholesterol

"good" and "bad" cholesterol refer to the type of carrier molecule that transports the cholesterol. These carrier molecules are made of protein and are called apoproteins. They are necessary because cholesterol and other fats (lipids) can't dissolve inwater, which also means they can't dissolve in blood. When these apoproteins are joined with cholesterol, they form a compound called lipoproteins. The density of these lipoproteins is determined by the amount of protein in the molecule. "Bad" cholesterol is thelow-density lipoprotein (LDL), the major cholesterol carrier in the blood. High levels of these LDLs are associated with atherosclerosis. "Good" cholesterol is the high-density lipoprotein (HDL); a greater level of HDL--think of this as drain cleaner you pour in the sink--is thought to provide some protection against artery blockage.

What is the Job description of HDL and LDL?

A high level of LDL in the blood may mean that cell membranes in the liver have reduced the number of LDL receptors due to increased amounts of cholesterol inside the cell. After a cell has used the cholesterol for its chemical needs and doesn't need any more, it reduces its number of LDL receptors. This enables LDL levels to accumulate in the blood. When this happens, the LDLs begin to deposit cholesterol on artery walls, forming thick plaques. In contrast, the HDLs--the "good" guys--act to remove this excess cholesterol and transport it to the liver for disposal.

A third group of carrier molecules, the very low-density lipoproteins (VLDL) are converted to LDL after delivering triglycerides to the muscles and adipose (fat) tissue.

The levels of HDL, LDL and total cholesterol are all indicators for atherosclerosis and heart attack risk. People who have a cholesterol level of 275 or greater (200 or less is desirable) are at significant risk for a heart attack, despite a favorable HDL level. In addition, people who have normal cholesterol levels but low HDL levels are also at increased risk for a heart attack.

Cholesterol Testing and Prevention

How often should I have my cholesterol levels tested?You should get your cholesterol tested every three to five years, more often if you have high cholesterol levels. Please refer to the table below for guidelines for total cholesterol, LDL and HDL levels.

	Desirable	Borderline	Undesirable
Total Cholesterol	Below 200	200-240	Above 240
HDL Cholesterol	Above 45	35-45	Below 35
LDL Cholesterol	Below 130	130-160	Above 160
Total Cholesterol/HDL	Below 4.5	4.5-5.5	Above 5.5
LDL/HDL	Below 3	3-5	Above 5

Cholesterol Risk Factors

There are a number of factors that influence a person's cholesterol levels. They include diet, age, weight, gender, genetics, diseases and lifestyle.

DietThere are two dietary factors associated with increases in blood cholesterol levels:

• Eating foods that are high in saturated fats, even if the fats themselves do not contain cholesterol. (These include foods containing high levels of hydrogenated vegetable oils, especially palm and coconut oils, avocados and other high-fat foods of vegetable origin.) 
   
• Eating foods containing high levels of cholesterol. (This group includes eggs and red meat--the most maligned of the cholesterol culprits--as well as lard and shrimp. These foods can significantly raise blood cholesterol levels, especially when combined with foods that are high in saturated fat.)

It's important to note that only foods of animal origin contain cholesterol. Lack of awareness of this fact has led to some confusing labels at the grocery store. For example, some items that are high in saturated fats from plant sources bear labels claiming that they are 100 percent cholesterol free. The statement may be true, but it's generally misleading because it implies that the product is definitely beneficial to your health.

AgeThe blood levels of cholesterol tend to increase as we age--a factor doctors consider when deciding treatment options for patients with certain cholesterol levels.

Weight
People who are overweight are more likely to have high blood cholesterol levels. They also tend to have lower HDL levels. The location of the excess weight also seems to play a role in cholesterol levels. A greater risk of increased cholesterol levels occurs when that extra weight is centered in the abdominal region, as opposed to the legs or buttocks.

Gender
Men tend to have higher LDL levels and lower HDL levels than do women, especially before age 50. After age 50, when women are in their post-menopausal years, decreasing amounts of estrogen are thought to cause the LDL level to rise.

GeneticsSome people are genetically predisposed to having high levels of cholesterol. A variety of minor genetic defects can lead to excessive production of LDLs or a decreased capacity for their removal. This tendency towards high cholesterol levels is often passed on from parents to their children. If your parents have high cholesterol, you need to be tested to see if your cholesterol levels are also elevated.

DiseasesDiseases such as diabetes can lower HDL levels, increase triglycerides and accelerate the development of atherosclerosis. High blood pressure, or hypertension, can also hasten the development of atherosclerosis, and some medications used to treat it can increase LDL and triglycerides and decrease HDL levels.

LifestyleFactors that negatively affect cholesterol levels also include high levels of stress, which can raise total cholesterol levels, and cigarette smoking, which can lower a person's HDL level as much as 15 percent. On the other hand, strenuous exercise can increase HDL levels and decrease LDL levels. Exercise also can help reduce body weight, which, in turn, can help reduce cholesterol. Recent research has shown that moderate alcohol use (one drink per day for women, two drinks a day for men) can raise HDL cholesterol and therefore reduce the risk of heart attack. Despite such research, it is difficult to recommend the habitual use of alcohol, because there are also negative health consequences associated with alcohol use and a high potential for abuse.

Always remember that risk factors for high cholesterol and cardiovascular disease don't exist in a vacuum--they tend to amplify each other. Reducing the risk of a cardiovascular disease involves eliminating all of the risk factors that we can control and seeking medical advise for those we can't.

Sources:

• special thanks to Sir Nofil Safwan for highlighting this topic of  General Science and ability.
• Howstuffworks, a site i personally love to visit before going anywhere else. they are steadfast professionals and know what they post. 
• Samad for encouraging.