Cholesterol and Human Health
Ma Hongbao, Ph.D.
Department of Medicine, Michigan
State University
East
Lansing, Michigan, USA
Abstract
Cholesterol plays a
major role in human heart health and high cholesterol is a leading risk factor
for human cardiovascular disease such
as coronary heart disease and stroke. There are 102.3 million
American adults who have total blood cholesterol values of 200 mg/dl and
higher, and about 41.3 million. Cholesterol can be good (high-density
lipoprotein) or bad (low-density lipoprotein) to the cardiovascular system. For
the total cholesterol in blood: less than 200 mg/dl is desirable level, 200 to
239 mg/dl is the borderline high for heart disease, and 240 mg/dl and above is
High blood cholesterol. A person with this level of 240 mg/dl or above has more
than twice the risk of heart disease as someone whose cholesterol is below 200
mg/dl. Statin drugs are very effective for lowering LDL cholesterol levels and
have few immediate short-term side effects. Some bacteria can
change cholesterol in food to coprostanol that cannot be readily absorbed by
the body and some oral bacteria such as Lactobacillus acidophilus have
been commercial available for the cholesterol lowering.
Key Words: cardiovascular,
cholesterol,
health, heart, lipoprotein
Cholesterol is a waxy substance made by animal liver and also supplied
in diet through animal products such as meats, poultry, fish and dairy
products. Cholesterol is needed in the body to insulate nerves, make cell
membranes and produce certain hormones. However, the body makes enough
cholesterol, so any dietary cholesterol isn't needed.
Cholesterol plays a major role in human heart health. Cholesterol can be both good
and bad. High
cholesterol is a leading risk factor for human cardiovascular disease such as coronary heart disease and
stroke - America's
number one killer (Tabas 2002). Excess cholesterol in the bloodstream can form plaque (a
thick, hard deposit) in artery walls. The cholesterol or plaque build-up causes
arteries to become thicker, harder and less flexible, slowing down and
sometimes blocking blood flow to the heart. When blood flow is restricted,
angina (chest pain) can result. A heart attack will result when blood flow to
the heart is severely impaired and a clot stops blood flow completely. When there is too much LDL
cholesterol in the blood, it is deposited inside the blood vessels, where it
can build up to hard deposits and cause atherosclerosis, the disease process
that underlies heart attacks.
There are 102.3 million American adults who have
total blood cholesterol values of 200 mg/dl and higher, and about 41.3 million
American adults have levels of 240 mg/dl of cholesterol or above. Total blood cholesterol is
the most common measurement of blood cholesterol. Cholesterol is measured in
milligrams per deciliter of blood (mg/dl). A person’s health cholesterol
content is based on other risk factors such as age, gender, family history,
race, smoking, high blood pressure, physical inactivity, obesity and diabetes.
Cholesterol can be good or bad. High-density
lipoprotein (HDL) is called “good cholesterol” that is good for the
cardiovascular system and low-density lipoprotein (LDL) is called “bad
cholesterol” that is bad for the cardiovascular system. The standard test of
cholesterol is done after a 9-12 hours fast without food, liquids or pills. It
gives information about total cholesterol, LDL, HDL and triglycerides (blood
fats). The cholesterol content in blood is the key data for the health
information of cholesterol related (Table). If a person’s total cholesterol is
200 mg/dl or more, or his/her HDL cholesterol is less than 40 mg/dl, he/she
needs to have a lipoprotein profile done to determine LDL cholesterol and
triglyceride levels.
A person’s LDL cholesterol goal depends on how many
other risk factors he/she has: (1) If he/she does not have coronary heart
disease or diabetes and have one or no risk factors, his/her LDL goal is less
than 160 mg/dl. (2) If he/she does not have coronary heart disease or diabetes
and have two or more risk factors, his/her LDL goal is less than 130 mg/dl. (3)
If he/she has coronary heart disease or diabetes, his/her LDL goal is less than
100 mg/dl.
|
Cholesterol |
Cholesterol Level |
Category |
|
Total
Cholesterol |
Less
than 200 mg/dl |
Desirable
level. |
|
200
to 239 mg/dl |
Borderline
high for heart disease. |
|
|
240
mg/dl and above |
High
blood cholesterol. A person with this level has more than twice the risk of
heart disease as someone whose cholesterol is below 200 mg/dl. |
|
|
HDL
Cholesterol |
Less
than 40 mg/dl |
Low
HDL cholesterol. A major risk factor for heart disease. |
|
40
to 59 mg/dl |
The
higher HDL level, the better. |
|
|
60
mg/dl and above |
High
HDL cholesterol. An HDL of 60 mg/dl and above is considered protective
against heart disease. |
|
|
LDL
Cholesterol |
Less
than 100 mg/dl |
Optimal |
|
100
to 129 mg/dl |
Near
or above optimal |
|
|
130
to 159 mg/dl |
Borderline
high |
|
|
160
to 189 mg/dl |
High |
|
|
190
mg/dl and above |
Very
high |
|
|
Triglyceride |
Less
than 150 mg/dl |
Normal |
|
|
150-199
mg/dl |
Borderline
high |
|
|
200-499
mg/dl |
High |
|
|
500
mg/dl and above |
Very
high |
Triglyceride is the most common type of fat in the
body. Many people who have heart disease or diabetes have high triglyceride
levels. Normal triglyceride levels vary by age and sex. A high triglyceride
level combined with low HDL cholesterol or high LDL cholesterol seems to speed
up atherosclerosis, which is the buildup of fatty deposits in artery walls that
increase the risk for heart attack and stroke.
People should reduce the amount of saturated fat, trans-fat,
cholesterol and total fat in their diet. Some studies have shown a higher
mortality in people with low cholesterol levels - that is, lower than 160
mg/dl. These deaths are from non-coronary causes (some cancers, chronic
respiratory disease, liver disease and trauma). On the other hand, some
evidence suggests that total cholesterol levels below 160 mg/dl are not
dangerous. In many countries a major portion of the population has cholesterol levels
in this range throughout life without serious health problems. Also, less than
6 percent of the American population has a cholesterol level below 160 mg/dl.
It's rarely necessary to lower total cholesterol below that.
Hyperlipidemia is an elevation of lipids (fats) in
the bloodstream. These lipids include cholesterol, cholesterol esters
(compounds), phospholipids and triglycerides. They're transported in the blood
as part of large molecules called lipoproteins. These are the five major
families of blood (plasma) lipoproteins: (1) chylomicrons, (2) very low-density
lipoproteins (VLDL), (3) intermediate-density lipoproteins (IDL), (4)
low-density lipoproteins (LDL), (5) high-density lipoproteins (HDL). When hyperlipidemia is
defined in terms of class or classes of elevated plasma lipoproteins, the term
hyperlipoproteinemia is used. Hypercholesterolemia is the term for high
cholesterol levels in the blood. Hypertriglyceridemia refers to high
triglyceride levels in the blood. The average American man gets about 337 mg of
cholesterol a day from food and the average woman gets about 217 mg. I suggest
that a person should limit cholesterol from food to an average of no more than
300 mg per day.
The drugs of first choice for elevated LDL
cholesterol are the HMG CoA reductase inhibitors, e.g. lovastatin, pravastatin
and simvastatin. Statin drugs are very effective for lowering LDL cholesterol
levels and have few immediate short-term side effects (Jongh et al. 2002). They are easy to administer, have high patient
acceptance and have few drug-drug interactions. Patients, who are pregnant,
have active or chronic liver disease, or those allergic to statins shouldn't
use statin drugs. The most common side effects of statins are gastrointestinal,
including constipation and abdominal pain and cramps. These symptoms are
usually mild to severe and generally subside as therapy continues. Another
class of drugs for lowering LDL is the bile acid sequestrants - cholestyramine
and colestipol - and nicotinic acid. These have been shown to reduce the risk
for coronary heart disease in controlled clinical trials. Both classes of drugs
appear to be free of serious side effects. But both can have troublesome side
effects and require considerable patient education to achieve adherence.
Nicotinic acid is preferred in patients with triglyceride levels exceeding 250
mg/dl because bile acid sequestrants tend to raise triglyceride levels.
Other available drugs are gemfibrozil, probucol and
clofibrate. Gemfibrozil and clofibrate are most effective for lowering elevated
triglyceride levels. They moderately reduce LDL cholesterol levels in
hypercholesterolemic patients, but the American FDA hasn't approved them for
this purpose. Probucol also moderately lowers LDL levels and it has been received
FDA approval for this purpose.
If a patient doesn't respond adequately to single
drug therapy, combined drug therapy should be considered to further lower LDL
cholesterol levels. For patients with severe hypercholesterolemia, combining a
bile acid sequestrant with either nicotinic acid or lovastatin has the
potential to markedly lower LDL cholesterol. For hypercholesterolemic patients
with elevated triglycerides, nicotinic acid or gemfibrozil should be considered
as one agent for combined therapy.
Some bacteria can change cholesterol in food to
coprostanol that cannot be readily absorbed by the body. These kind of bacteria
are called friendly bacteria. This helps recycle cholesterol to make hormones. Bifidobacterium
and Lactobacillus acidophilus may play an important role in cholesterol
metabolism of their host. Intestinal bacteria convert cholesterol into a less
absorbable form coprostanol thus hampering its absorption from the intestinal
tract (Lin and Chen 2000). Lactic acid bacteria in intestine have the
cholesterol lowering effect (Pereira and Gibson 2002). Some oral bacteria such
as Lactobacillus acidophilus have been commercial available for the
cholesterol lowering. Feeding friendly bacteria can do: (1) reduce the growth
of unfriendly bacteria, (2) maintain regular bowel movements, (3) maintain
cholesterol and triglyceride levels, (4) maintain healthy blood sugar levels.
There are a
variety of medications available for lowering blood cholesterol levels. They
may be prescribed individually or in combination with other drugs. Some of the
common types of cholesterol-lowering drugs include statins, resins and
nicotinic acid (niacin), gemfibrozil, and clofibrate:
1.
Clofibrate (Atromid-S).
This drug raises the HDL cholesterol levels and lowers triglyceride levels.
2.
Gemfibrozil (Lopid).
This drug lowers blood fats and raises HDL cholesterol levels.
3.
Nicotinic Acid.
This drug works in the liver by affecting the production of blood fats. It's
used to lower triglycerides, lower LDL cholesterol and raise HDL cholesterol.
4.
Resins. Resins are
also called bile acid-binding drugs. They work in the intestines by promoting
increased disposal of cholesterol. There are three kinds of medications in this
class: Cholestryamine (Questran, Prevalite, Lo-Cholest),
Colestipol (Colestid), Coleseveiam (WelChol).
5.
Statins. Statin drugs
are very effective for lowering LDL cholesterol levels and have few immediate
short-term side effects. They work by interrupting the formation of cholesterol
from the circulating blood. Commonly prescribed statins include: Atorvastatin
(Lipitor), Cerivastatin (Baycol), Fluvastatin (Lescol), Lovastatin (Mevacor),
Pravastatin (Pravachol), Simvastatin (Zocor).
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M, Chen T. Reduction of cholesterol by Lactobacillus Acidophilus in
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