Encyclopedia of Health and Medicine

36 The Cardiovascular System
culation exceeds the body’s needs. The excess
lipoproteins that transport the cholesterol fall out
of suspension and infiltrate the inner lining of the
arterial walls, forming ATHEROSCLEROTIC PLAQUE.
Health factors that increase the risk of elevated
lipoprotein-cholesterol blood levels include OBE-
SITY, DIABETES, and HYPERTENSION.
The LIVER produces most of the cholesterol in
the blood circulation, manufacturing this necessary
chemical from saturated fats and other
dietary NUTRIENTS. Dietary cholesterol is a minor
factor in this process. The liver continues to manufacture
cholesterol as long as it receives the
ingredients, via ingested nutrients, to do so. Cells
throughout the body also can synthesize cholesterol
to meet their needs. The body stores some
excess cholesterol, along with other fatty acids
(notably triglycerides), in adipose tissue throughout
the body. The body can then withdraw this
cholesterol when liver synthesis slows. However,
adipose tissue can hold only so much. Remaining
excess cholesterol stays in the bloodstream.
The liver manufactures the lipoproteins that
carry cholesterol as well as triglycerides and phospholipids
(collectively called fatty acids or lipids).
Different lipoproteins transport the kinds of fatty
acids. Very low-density lipoprotein (VLDL) and
low-density lipoprotein (LDL) transport some cholesterol
and most of the triglycerides. It is the
excesses of LDL cholesterol (LDL-C) and VLDL cholesterol
(VLDL-C) that create increased cardiovascular
health risks. These lipoprotein packages settle
out of the blood easily, collecting against the inner
walls of the arteries. Over time (typically decades)
the lipoproteins, along with other cellular debris
that gathers, infiltrates the innermost layer of the
arterial wall and forms atherosclerotic plaque. This
process is the foundation of ATHEROSCLEROSIS.
High-density lipoprotein (HDL) transports primarily
cholesterol. It appears that HDL not only
carries cholesterol from the liver but also picks up
fragments of cholesterol-bearing LDL and VLDL
and returns them to the liver, which disassembles
them. Lowering the available lipoproteins in the
body reduces the excess circulating in the bloodstream
and increases the proportion of HDL cholesterol
(HDL-C) to LDL-C/VLDL-C. Cells draw the
cholesterol they need from the supply in circulation,
helping maintain a healthy balance. Generally,
the higher a person’s total cholesterol, the
higher his or her LDL-C levels.
ADDITIONAL CARDIOVASCULAR RISK FACTORS
age 65 or older
CONGENITAL HEART DISEASE
DIABETES
family history of CARDIOVASCULAR
female past MENOPAUSE DISEASE (CVD)
HYPERTENSION
HEART ATTACK
male, any age
ISCHEMIC HEART DISEASE (IHD)
PERIPHERAL VASCULAR
OBESITY
DISEASE (PVD)
physically inactive
smoking
STROKE
TRANSIENT ISCHEMIC ATTACK
When the body’s nutrient intake is in balance,
the liver uses up the nutrient components available
to manufacture cholesterol and lipoproteins,
sending into circulation the levels that the body
can use. “Optimal” blood cholesterol values identify
this balance, or lipid homeostasis, in which
there is no increased cardiovascular risk in most
people. Researchers have recently determined the
LDL level to be the most significant in people who
have other RISK FACTORS FOR CARDIOVASCULAR DIS-
EASE.
Current lipid-lowering treatment recommendations
emphasize LDL-C blood values; the recom-
CHOLESTEROL-LOWERING MEDICATION RECOMMENDATIONS
LDL-C Level Risk Factor Profile Target LDL-C Level
< 100 mg/dL CVD + 2 or more CVD risk factors 100 mg/dL
130–160 mg/dL CVD 100 mg/dL
160–190 mg/dL 2 or more CVD risk factors 130 mg/dL
> 190 mg/dL no CVD or risk factors 160 mg/dL
190–219 mg/dL male under age 35 160 mg/dL
190–219 mg/dL female premenopause 160 mg/dL