Other Lipoproteins Being Studied

As if HDL, LDL, and VLDL weren’t enough to track, researchers are discovering other types of lipoproteins that play a role in your 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-mikrons) give rise to all other forms of lipoproteins. When you eat, the fat in your meal passes through your digestive system into your intestine. There the cells lining the small intestine transform the fat. into small droplets of fat and protein that contain cholesterol and triglycerides. These droplets are the chylomicrons,

They head out of your gut and into your bloodstream, eventually encountering enzymes that break them down into chylomicron remnants. The remnants continue on to your liver, where they’re repackaged as other forms of cholesterol and triglycerides, The reason that statins, the major class of cholesterol-lowering drugs (Zocor, Lipitor. Pravachol, ete.), don’t work very well to lower triglyceride levels is that they don’t seem to affect chylomicrons, the major transporter of triglycerides. (We’ll talk more about statins in Chapter 8.)

Researchers dlon’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 (more on this in Chapter 5) 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)—doctors call it “el-pee little-a”—is found only the blood of hedgehogs, certain monkeys, and humans. It’s 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 Although Lp(a) carries significant in women. The landmark Heart and Estrogen/Progestin only a small amount of Replacement Study (HERS) found that women with the highest Lp(a) levels had a 54 percent greater risk of recurrent heart problems than those with the lowest levels. And the farmingham Heart Study found that levels above 30 mg/dl doubled the risk of heart attack in 3,000 women.

Although Lp(a) carries only a small amount of cholestrol, an elevated level is three to four times more powerful as a marker of heart diease than other measure such as LDL

While there is no official target level for Lp(a), studies suggest that for many people, levels starting at 30mg/dl may raise your risk of heart diseases.African-Americans are the exception; their levels are typically two to three times higher than those of Caucasians.

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.


As noted earlier, 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. HDL pairs with apolipoprotein A—or apo(a) for short— and LDL bonds with apolipoprotein B—apo(b). 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 docters 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, so don’t expect to have one; it isn’t part of the typical complete lipid profile, either. 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.

Thus, a high apo(b) level may be the tiebreaker to help your doctor decide whether to start you on cholesterol lowering drugs, There’s also some thought that apo(b) may actually turn out to be a very accurate indicator of heart disease risk in women, whose triglyceride levels tend to run high to begin with.

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 forwomen 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 tigiveerides, chylomicrons, chylomicron remnants, VLDL, VLDL remnants, and IDL. They’re veritable stuffed balloons of risk factors for heart disease. In one major Japanese study, researchers measured levels of total cholesterol, LDL, HDL, triglycerides, Lp(a), and RLP-C in the blood of 208 patients, of whom 57 had high cholesterol and 151 had normal cholesterol. They found that an unfavorable ratio of RLP-C to HDL (a normal ratio is less than 1:4) in patients with overall normal cholesterol levels was highly associated with narrowing of the coronary arteries. In other words, here’s a clear example of why having a normal total cholesterol level may not be good enough to prevent heart disease Currently, there is no readily available test for RLP-C levels, although as more research emerges on its role in cardiac disease, thal w ill change

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