Cholestrol

Cholesterol is an organic molecule. It is a modified steroid and an essential structural component of animal cell membranes that is required to establish proper membrane permeability (movement of molecules through the membrane) and fluidity.Cholesterol is thus considered a kind of lipid molecule.It also serves as a precursor (starting material) for the biosynthesis of steroid hormones, bile acids, and vitamin D. Most ingested cholesterol (cholestrol taken in the diet) is esterified (addition of ester groups i.e. R1-COO-R2) and esterified cholesterol is poorly absorbed. The body also compensates for any absorption of additional cholesterol by reducing cholesterol synthesis. It is recycled. The liver excretes it in a non-esterified form (via bile) into the digestive tract. Typically about 50% of the excreted cholesterol is reabsorbed by the small bowel back into the bloodstream. When the cholesterol levels in the blood are too high, it can cause increase in the risk factors for heart disease.

Types of cholestrol-

1) High density lipoproteins-

They are also known as HDL, is considered the "good" cholesterol. HDL is produced by the liver to carry cholesterol and other lipids (fats) from tissues and organs back to the liver for recycling or degradation. High levels of HDL are a good indicator of a healthy heart, because less cholesterol is available in your blood to attach to blood vessels and cause plaque formation. 

According to the National Cholesterol Education Program:

• Any HDL level above more than 60 mg/dL (1.56 mmol/L) is considered high. A high HDL level is considered very healthy, since it has a protective role in guarding against heart disease.
• An acceptable HDL range is between 40- 60 mg/dL (1.04–1.56 mmol/L).
• An undesirable level of HDL is any level below 40 mg/dL (1.04 mmol/L). In this case, low HDL levels may help to contribute to heart disease.

2) Low Density Lipoproteins-

Low density lipoproteins, also referred to as LDL, is known as the "bad cholesterol". LDLs are produced by the liver and carry cholesterol and other lipids (fats) from the liver to different areas of the body, like muscles, tissues, organs, and the heart. It is very important to keep LDL levels low, because high levels of LDL indicate that there is much more cholesterol in the blood stream than necessary, therefore increasing your risk of heart disease. LDLs are calculated by using an equation involving total cholesterol, triglycerides, and HDLs--all of which are measured directly in the blood:

LDL = TC – (triglycerides/5) + HDL)

The following guidelines have been set forth by the National Cholesterol Education Program:

• LDL levels less than 100 mg/dL ( 2.6 mmol/L) are considered optimal.
• LDL levels between 100 – 129 mg/dL (2.6–3.34 mmol/L) are considered near or above optimal.
• LDL levels between 130 – 159 mg/dL (3.36–4.13 mmol/L) are considered borderline high.
• LDL levels between 160 – 189 mg/dL (4.14 - 4.90 mmol/L) are considered high.
• LDL levels at or above 190 mg/dL (4.91 mmol/L) is considered very high.

3) Very Low Density Lipoproteins-

Very low density lipoproteins, or VLDL, are lipoproteins that carry cholesterol from the liver to organs and tissues in the body. They are formed by a combination of cholesterol and triglycerides. VLDLs are heavier than low density lipoproteins, and are also associated with atherosclerosis and heart disease. This number is obtained by dividing your triglyceride levels by 5.

When a patient gets a lipid profile test done, there are three main types of cholesterol that are tested. Namely- LDL, HDL and VLDL. Triglycerides, another type of lipid in the blood, are also tested. The amounts of each lipid in your blood will allow the patient's health care provider to predict his risk for getting heart disease in the future.

A cholesterol test is done to diagnose a lipid disorder.  Everyone should have their first screening test by age 35 in men, and age 45 in women.