Cholesterol is one of the most recognized and most misunderstood blood
tests available. A high blood level of cholesterol can unnecessarily create
fear while a “normal” blood level can make one wrongly feel
safe. Let’s take a look at the real story behind cholesterol.
Cholesterol is necessary for life. Without it your cell membranes would
not function properly. In addition, critically important substances like
steroid hormones (cortisol), sex hormones (testosterone), bile acids that
allow for the absorption of fat, and Vitamin D require cholesterol as
part of their biosynthesis.
The cholesterol in your blood comes from two sources. It is either absorbed
in your small intestine from your diet or synthesized in your liver. Of
these two mechanisms your liver is the source of the majority of the cholesterol
we measure in blood. There is an intricate regulation of the rate at which
cholesterol is made in the liver in balance with the amount absorbed through
the diet and the level of cholesterol in the blood.
The cholesterol in the blood is a fat and the blood is essentially water
based. So, much like pouring oil in water, the cholesterol cannot travel
in blood by itself or it would separate. To accomplish this, the body
packages the cholesterol inside a protein covering that can travel in
the blood throughout the body to be used in the normal physiology of living.
It is these lipoproteins that are responsible for most of the heart disease
risk. They are distinguished in several ways, but most commonly by their
density, so you see LDL (low density lipoproteins), VLDL (very low density
lipoprotein), and HDL (high density lipoproteins), in a “Cholesterol
Blood Panel”.
The trouble arises when either through a genetic propensity, poor lifestyle
choices with a high fat diet, or a sedentary lifestyle accompanied by
weight gain, that the blood levels of cholesterol increase. Above a certain
point, it appears the cholesterol circulating in your blood as it interacts
with certain substances becomes oxidized and makes its way under the inner
lining (intima) of arteries in the body. Diets high in trans-fats, smoking,
poorly controlled diabetes and metabolic syndrome increases the likelihood
of oxidation. Through a series of subintimal interactions involving inflammation
an atheroma or plaque forms, narrowing the artery over time.
We now know that not all cholesterol is created equal. For example we
now know that the LDL “Bad” cholesterol is made up of seven
sub fractions, some of which are more atherogenic and likely to become
oxidized and slip under the intimal lining of the artery. For example,
an LDL with predominantly small, dense particles (Pattern B) may be much
more risky that the same LDL level with predominantly larger more buoyant
particles (Pattern A). Furthermore, some recent evidence suggests the
number of particles (LDL-P) may be even more important than the density
profile of LDL. In a similar way the HDL is composed of 5 subunits, some
of which may be more protective that others. Finally, it now looks like
it may be the number of each type of particle that matters most, making
measuring LDL-P(particles) and HDL-P(particles) important in determining
risk factors.
As you can see, our understanding of heart disease and cholesterol is
constantly advancing. So when evaluating your cholesterol, it is important
to consider the latest information we have about cholesterol and dig deeper
than just the “good” (HDL) and the “bad” (LDL)
levels. A complete understanding of cholesterol as a risk factor should
include important genetic markers, an HDL and LDL phenotype with each
of their respective sub-fractions, and LDL particle count (LDL-P) and
markers of inflammation to evaluate oxidation risk. Only a comprehensive
evaluation of cholesterol in your blood can assure that you are acting
on the complete picture, allowing for a personalized and more precise
action plan.
Written by James Lindberg, M.D., Hoag Executive Health Chief of Service