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.
