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Understanding Cholesterol

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