Cholesterol is a waxy fat that is present
in all human beings. Two sources contribute to the amount
of cholesterol in the human body. First, the liver manufactures
about 80 percent of it. Second, people consume it by eating
animal products such as meat, eggs and dairy products. Cholesterol
is carried through the bloodstream by certain proteins (apolipoproteins).
When these proteins wrap around cholesterol and other types
of fats (lipids) to transport them through the bloodstream,
the resulting "packages" are called lipoproteins.
There are four different types of lipoproteins that carry
cholesterol through the bloodstream:
" High-density lipoproteins (HDL), which are associated
with "good" cholesterol.
" Low-density lipoproteins (LDL), which are associated
with "bad" cholesterol.
" Very-low-density lipoproteins (VLDL), which
are associated with "very bad" cholesterol.
" Chylomicrons, which only carry a small percentage of
cholesterol. Chylomicrons are mostly rich in another type
of fat (lipid) called triglycerides.
The National Cholesterol Education Program classifies cholesterol
levels as follows (all measurements are in milligrams per
deciliter):
" Total cholesterol levels less than 200 are desirable.
" Total cholesterol levels between 200 and 239 are borderline-high.
" Total cholesterol levels that are 240 or higher are
high.
" HDL levels should be 40 or above.
" LDL levels should optimally be less than 100 (levels
greater than 129 are considered borderline-high, and levels
greater than 159 are considered high).
What is cholesterol?
Cholesterol is a fat-like substance (lipid). It is both produced
in the liver and consumed by eating animal products such as
meat, eggs or dairy products. The body needs cholesterol
and manufactures all the cholesterol needed by various organ
systems. In fact, the body naturally produces up to four times
more cholesterol than what would be normally be taken in through
diet. The body uses cholesterol to:
- Assist in the manufacture of hormones or vitamin D
- Break down carbohydrates and proteins
- Help form a protective coating around nerves
- Build cell walls and to produce bile (the word cholesterol
is Greek for “bile solids”)
- Cholesterol is carried through the bloodstream by lipoproteins.
Lipoproteins are proteins that wrap around both cholesterol
and other fatty materials and transport them through the
bloodstream.
Two types of lipoproteins carry most of the cholesterol in
the bloodstream, and they behave very differently from each
other as they move through the body:
- High-density lipoproteins (HDL). “Good” cholesterol,
HDLs move easily through the blood and are actually beneficial
to the body. They are stable and do not stick to artery
walls. They help to prevent heart disease by carrying cholesterol
away from the arteries and back to the liver, where the
process of their removal from the body begins.
- Low-density lipoproteins (LDL). “Bad” cholesterol,
LDLs contain more fat and less protein than HDLs. LDLs are
unstable; they tend to fall apart. Rather than being removed
from the body by the liver, they stick to (and can damage)
cells lining the inside of artery walls. Areas of cell damage
provide a magnet-like attraction for other fatty substances
(e.g., triglycerides), sticky blood-clotting materials (e.g.,
fibrin and platelets) and white blood cells. The waxy accumulation
of these materials is known as plaque. This can eventually
lead to hardened arteries (atherosclerosis) or coronary
artery disease. Therefore, high levels of LDLs are strongly
associated with increased risk for heart disease. Many people
with high levels of "bad" cholesterol also have
high triglyceride levels because both types of fats have
similar risk factors (e.g., obesity and diabetes).
- Smaller amounts of cholesterol may travel in “very
bad” cholesterol (very low-density lipoproteins [VLDLs])
or another type of lipoprotein called chylomicrons (which
are rich in triglycerides). VLDLs and so-called intermediate-density
lipoproteins (IDLs) belong to a newer category known as
non-HDL cholesterol. Studies are showing that high non-HDLs
can raise the risk of non-fatal heart attack and angina
among individuals who already have heart disease.
Advances in research techniques have allowed for more in-depth
measurements of cholesterol. Lipoprotein “a” –
abbreviated Lp(a) – is a type of cholesterol that is
associated with increased risk of heart disease when values
are greater than approximately 30 milligrams per deciliter.
Apolipoprotein B (apo-B) has been shown to be helpful in determining
cardiovascular risk in women.
What causes high cholesterol levels?
The cholesterol value in the human body can rise to abnormally
high levels when someone eats a diet high in saturated fats
or trans fats – especially when
that person is obese and/or rarely exercises.
High cholesterol levels can also be caused by a number of
different genetic conditions. The most widespread inherited
cholesterol disorder is familial hypercholesterolemia (FH).
The cholesterol levels of people with this disorder may reach
as high as 550 milligrams per deciliter – almost four
times the level considered desirable for the average person.
With cholesterol this high, people with FH are at a high risk
for an early heart attack, regardless of the presence of other
risk factors. If FH is suspected, children as young as two
years of age may be appropriate for a cholesterol screening.
Another genetic condition associated with high cholesterol
levels is familial dysbetalipoproteinemia (or familial combined
hyperlipoproteinemia) in which both cholesterol and triglyceride
levels are elevated.
What is the link between high cholesterol
and heart disease?
The medical term for an excessive amount of cholesterol
in the blood (over 240) is hypercholesterolemia. It is one
of the greatest threats to someone’s health. Not only
is it a major contributor to the development of hardened arteries
(atherosclerosis), but it can also lead to a certain type
of chest pain called angina, or even a heart attack. Research
studies have concluded that for every 1 percent reduction
in blood cholesterol level, the risk of coronary heart disease
decreases by as much as 3 percent.
What cholesterol levels are considered
high or low?
According to the most recent guidelines from the National
Heart, Lung and Blood Institute (NHLBI), cholesterol levels
are classified as follows:
| Total Cholesterol Level
| Category |
| Less than 200 mg/dL |
Desirable |
| 200 to 239 mg/dL |
Borderline high |
| 240 mg/dL and higher |
High |
| LDL Cholesterol Level
| Category |
| Less than 100 mg/dL |
Optimal |
| 100 to 129 mg/dL |
Near optimal/above optimal |
| 130 to 159 mg/dL |
Borderline high |
| 160 to 189 mg/dL |
High |
| 190 mg/dL and higher |
Very high |
| HDL Cholesterol Level
| Category |
| Less than 40* mg/dL |
Low (increased risk) |
| 60 mg/dL and higher |
High (heart-protective) |
It is recommended
that women maintain HDL cholesterol levels of at least 45.
| Triglyceride Level
| Category |
| Less than 150 mg/dL |
Normal |
| 150 to 199 mg/dL |
Borderline high |
| 200 to 499 mg/dL |
High |
| 500 mg/dL and higher |
Very high |
Labs outside of the United States may use different units
of measure for cholesterol levels. To convert a cholesterol
level from milligrams per deciliter (mg/dL) to international
units (IU), multiply the mg/dL cholesterol level by 0.0259
millimoles per liter (mmol/L). For example, a cholesterol
level of 200 mg/dL is equal to a cholesterol level of 5.18
IU.
Hypercholesterolemia, or high cholesterol, is diagnosed
by measuring total cholesterol levels, as well as by separate
HDL ("good") and LDL ("bad") levels. The total cholesterol
equals HDLs + LDLs + 1/5 triglycerides. Another calculation
gives the cholesterol ratio, which is the total cholesterol
divided by the HDL level. The level of total cholesterol should not be
more than five times the level of good cholesterol. This
may also be expressed as the ratio 5:1. Test results may
include this important ratio. Ratios such as 4:1 or 3:1
are more desirable, and ratios such as 6:1 or 7:1 are less
desirable. Furthermore, experts generally recommend that
the level of HDL cholesterol should be at least 35 milligrams
per deciliter, regardless of total cholesterol level.
Low total cholesterol (below 160) is not directly harmful
to the human body but could indicate the presence of other
medical conditions that may require attention. These medical
conditions include the following:
- Hyperthyroidism. An overactive thyroid gland that leads
to an excess of thyroid hormone in the body.
- Malnutrition. Inadequate nutrition that may be caused
by an unbalanced diet or a condition in which the body
has difficulty digesting or absorbing nutrients from food
(malabsorption).
- Pernicious anemia. A type of anemia (red blood cell
deficiency) caused by the lack of a substance in the body
needed to absorb vitamin B-12.
- Sepsis. A serious bacterial infection that has spread
to the blood.
Who needs cholesterol screening and how
often?
Regular cholesterol screenings are important. The National
Cholesterol Education Program recommends that both males
and females 20 years of age and older have a "lipid
profile" (or cholesterol test) every five years. Regular
cholesterol screenings are particularly important for people
who have risk factors such as diabetes, obesity or a family
history of cardiovascular disease. Such higher risk individuals,
and people over age 65, may be screened more frequently.
Even children can benefit from having their cholesterol
checked, because it is one way to identify factors that
may adversely affect their heart health as they grow. Furthermore,
starting young children on medication to treat high cholesterol
may be more of a risk than the early plaque build-up it
is meant to prevent.
Cholesterol screening is fast and relatively painless. Blood
is drawn from a vein or through a fingertip “prick
test.” Regular screenings are the first line of defense
against developing high cholesterol levels. If triglyceride
levels are going to be measured, test participants will
be asked to stop eating or drinking for approximately nine
hours prior to the screening.
This cholesterol screening is only an approximate indication
of one’s cholesterol level. Even under normal conditions,
the test results may be higher or lower than a person’s
actual cholesterol levels by about 14 percent. Also, test
results can vary quite a bit even when repeated over a short
period of time. Therefore, many physicians will provide
results as a cholesterol range (e.g., 150 to 160) rather
than an exact number.
Gender Differences in Cholesterol
Women benefit from cholesterol-lowering activities as much
as men do. However, they are far less likely to seek or
receive treatment for high cholesterol. Studies have suggested
that high LDL levels are not as significant a risk factor
for women as for men. Researchers suggest that apolipoprotein
B (apoB), a protein found in in low-density lipoproteins,
is the best cholesterol-related predictor of coronary artery
disease or women. As gender-specific research continues,
women will probably see an increased availability of information
and protocols for monitoring their cholesterol levels.
