What Exactly Is Cholesterol?

A substance your body can't live without

from Cut Your Cholesterol

As if HDL, LDL, and VLDL weren’t enough to track, researchers are discovering other types of lipoproteins that play a role in your coronary heart disease (CHD) risk. Again, the standard cholesterol test doesn’t measure them, but most are included in a complete lipid profile.

You probably haven’t heard of this class of lipoproteins, as researchers are just beginning to understand their role as a risk factor in CHD. But chylomicrons (ki-LO-mi-krons) give rise to all other forms of lipoproteins. Unfortunately statins, the major class of cholesterol-lowering drugs (Zocor, Lipitor, Pravachol, etc.), doesn’t seem to affect chylomicrons, the main carrier of triglycerides. This is why many cholesterol drugs don’t work very well to lower triglyceride levels.

Researchers don’t know why, but the higher the level of chylomicron remnants in your blood, the greater your risk of CHD. Certain cholesterol-lowering drugs, such as Lopid (gemfibrozil) and other fibrates, help lower your chylomicron level, as do supplements of fish oil. There are no established targets for chylomicrons. Because they are transient, they don’t sustain a stable blood level.

Lipoprotein (a), also known as Lp(a) is made up of a small portion of LDL, with an adhesive protein (apoprotein A) surrounding it. This gives Lp(a) a Velcro-like stickiness that makes it more likely to cause blood clots and lead to the formation of artery-narrowing plaques. It also seems to prevent clots from dissolving, increasing the danger that a clot will block the flow of blood to your heart or brain. Although Lp(a) carries only a small amount of cholesterol, an elevated level is three to four times more powerful as a marker of CHD than other measures, such as LDL.

If you have high Lp(a), your risk of developing CHD over the next 10 years is 70 percent higher than someone with normal levels. The risk is particularly significant in women where high levels can double the risk of heart attack. If you have a family history of heart disease, especially if you’re a woman nearing menopause or postmenopause, ask your doctor about having your Lp(a) level tested.

With all of that said, there’s not much you can do to modify your Lp(a) level. Unlike other kinds of cholesterol, Lp(a) in the blood is mainly determined by genes, so drugs and dietary changes have little effect on it. But that doesn’t mean there’s no point in finding out your level. If, for instance, you have high Lp(a) with another CHD risk factor, like smoking or being overweight, that could justify setting an even lower goal for your LDL or being more aggressive in your efforts to change your lifestyle.

Cholesterol can’t get around the body without hooking up with proteins that act as transporters. Different types of cholesterol tend to hook up with different types of proteins. Apolipoprotein A, apo(a), and apolipoprotein B, apo(b), act as transporters for HDL and LDL respectively. So it’s no big surprise that a low level of apo(a) and a high level of apo(b) may indicate trouble.

One large study of people who had had heart attacks found that low apo(a) and high apo(b) levels quadrupled the odds of a second heart attack. The combination may also pose dangers for those who haven’t had a heart attack. In fact, research suggests that your apolipoprotein levels may predict your likelihood of having a heart attack even better than your LDL or HDL levels.

At some point doctors may start relying more on these protein levels as a sign of CHD risk. But right now the test is still relatively new, expensive, and not standardized for the basic doctor’s office. The exception is if you have a high triglyceride level that can make it more difficult to get an accurate reading of non-HDL cholesterol.

Normal ranges for apo(a) are 101-199 mg/dl for women and 94-178 mg/dl for men. For apo(b) normal ranges are 49-103 mg/dl for women and 52-109 mg/dl for men.

Remnant-Like Particle Cholesterol
One other form of cholesterol that researchers are studying is remnant-like particle cholesterol, referred to as RLP-C. These are lipoproteins that contain the greatest proportion of triglycerides, chylomicrons, chylomicron remnants, VLDL, VLDL remnants, and IDL. They’re veritable stuffed balloons of risk factors for heart disease.

Currently, there is no readily available test for RLP-C levels, although as more research emerges on its role in cardiac disease, that will change.