The Most Important Number May Be A Kind of Cholesterol Your Doctor Does Not Test

Everybody has heard the “clogged pipes” analogy of cholesterol and heart disease. Just as a ball of grease can stop your kitchen drain, the analogy goes, cholesterol can clog your own “pipes” and cause heart attack, stroke, or poor circulation.

There is just one problem with that analogy. Cholesterol never forms clogs. And arteries are most commonly closed off by clots formed by red blood cells, not clogs formed by cholesterol.

Even if you had a total cholesterol of 10,000 mg/dl, only about 10 per cent of your bloodstream would be cholesterol-and nobody ever has a total cholesterol reading of 10,000 mg/dl. The simple fact is that our bodies do not make enough cholesterol to clog our arteries. If you have a total cholesterol of 200, for example, then you have about half an ounce (15 grams) of cholesterol in your entire bloodstream. That would be a pretty big clog, except cholesterol doesn’t form clogs.

What cholesterol does that is detrimental to vascular health is to adhere to the lining of arteries where it is attacked by the immune system and calcifies. Calcified arteries become stiff, and eventually they can’t open themselves to keep blood flowing around a clot of red blood cells.

If cholesterol never “sticks” to the linings of arteries, you don’t get heart disease. If it never calcifies, you don’t get heart disease. If your arteries remain flexible despite calcified cholesterol deposits, you don’t get heart disease.

And it is not every kind of cholesterol that hardens into plaques. It’s just LDL cholesterol, and it’s not even every form of LDL cholesterol.

Cholesterol is a fat, and the bloodstream is mostly water. Fat doesn’t dissolve in water, so every kind of cholesterol has to be attached to a carrier molecule to travel through the bloodstream. Larger pieces of LDL cholesterol are attached to a carrier molecule called apolipoprotein-A. Smaller, denser pieces of LDL cholesterol are attached to a carrier molecule called apolipoprotein-B.

If cholesterol is bound to apolipoprotein-A, it doesn’t calcify in the lining of arteries. If cholesterol is bound to apolipoprotein-B, then it usually does wind up forming a hardened, calcified plaque in the lining of some artery.

The only kind of cholesterol that causes cardiovascular disease is LDL that is attached to apolipoprotein-B, also known as apo-B. If you have high LDL and it’s all attached to apo-B, or mostly attached to apo-B, then you are at higher risk for heart disease. If you have high LDL and it’s attached to apo-A, then there is no health issue, other than maybe your doctor’s hair catching on fire when reading your lab reports.

Your total cholesterol, your LDL cholesterol number, your HDL cholesterol number, and your triglyceride numbers help doctors make educated guesses, but that’s all they are. The one kind of cholesterol that makes a difference is apo-B. But as you will read in the article on cholesterol and triglycerides, doctors almost never measure it!