Facts on File Encyclopedia of Health and Medicine

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 LIVERproduces most of the cholesterol in
the blood circulation, manufacturing this neces-
sary chemical from saturated fats and other
dietary NUTRIENTS. Dietary cholesterol is a minor
factor in this process. The liver continues to man-
ufacture cholesterol as long as it receives the
ingredients, via ingested nutrients, to do so. Cells
throughout the body also can synthesize choles-
terol to meet their needs. The body stores some
excess cholesterol, along with other fatty acids
(notably triglycerides), in adipose tissue through-
out 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 phos-
pholipids (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 cho-
lesterol and most of the triglycerides. It is the
excesses of LDL cholesterol (LDL-C) and VLDL cho-
lesterol (VLDL-C) that create increased cardiovas-
cular 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 pri-

marily 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 blood-

stream and increases the proportion of HDL cho-

lesterol (HDL-C) to LDL-C/VLDL-C. Cells draw the

cholesterol they need from the supply in circula-

tion, helping maintain a healthy balance. Gener-

ally, 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 pastMENOPAUSE 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 avail-

able to manufacture cholesterol and lipoproteins,

sending into circulation the levels that the body

can use. “Optimal” blood cholesterol values iden-

tify 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 recommenda-

tions emphasize LDL-C blood values; the recom-

36 The Cardiovascular System

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