What Exactly Is Cholesterol?
A substance your body can’t live without
Although cholesterol has gotten a bad rap over the years, it’s not, by itself, a bad thing.
Cholesterol is a soft, faintly yellow, naturally occurring waxy substance found in cell walls and membranes throughout your body, including your brain, nerves, muscles, skin, liver, intestines, and heart. It’s one of several fats, or lipids, your body produces. Without enough cholesterol, you simply couldn’t live.
You use cholesterol to produce sex hormones (including estrogen, progesterone, and testosterone), vitamin D, and bile acids that help you digest fat. However, you need only a relatively small amount to take care of all of these things. And your body (your liver, intestines, and even skin) manufactures plenty of it — about three or four times more cholesterol than most Americans eat. That means you could go the rest of your life without ever consuming another bite of cholesterol and you’d be just fine. (Although there’s no need to do so. In actuality, eating too many foods that contain cholesterol is not the main cause of high blood cholesterol.)
Like so many things, cholesterol isn’t bad for you unless there’s too much of it, at which point it begins to cause trouble. The story isn’t quite that simple, however. As you probably already know, there are different kinds of cholesterol — some bad, some good. And how much you have of each type makes a tremendous difference in your likelihood of developing coronary heart disease (CHD).
It’s actually not cholesterol per se that’s good or bad for you, but the “vehicle” through which it travels your bloodstream. Because cholesterol is waxy, it can’t mix with blood, which is watery. Like oil in a salad dressing, it remains separate. To enter the cells and tissues where it’s needed, then, it hooks up with proteins, creating special transporters called lipoproteins. Think of these as submarine-like bubbles that carry cholesterol around the body. Some of these “submarines” are friends, but most are foes.
Low-density lipoproteins, or LDLs, are the primary foes — the archenemies, in fact. LDLs carry most of the cholesterol (75 to 80 percent) in the blood, depositing it into the cells, including the arteries. There these particles contribute to the formation of plaque, which narrows the arteries. That reduces the amount of blood that can get through, diminishing the amount of oxygen that reaches the heart.
Some LDL types are more dangerous than others. Smaller, denser LDL particles are more damaging to blood vessels because it’s easier for them to cross the lining of the vessel and burrow into the vessel wall.
Most people won’t know what type of LDL they have because the tests to determine it are too expensive and complicated for the typical doctor’s office. If you already have coronary heart disease (CHD), or have a strong family history of CHD, and your doctor has sent you to a cardiac specialist, that doctor may run more detailed tests to better understand your risk. But it doesn’t matter much, as the focus remains the same regardless: Lower the amount of LDL in your body.
So what’s the ideal LDL level? That depends on your personal history and other risk factors for CHD. But if you’re a man 45 or older or a woman 55 or older and don’t have CHD, diabetes, hypertension, or a family history of premature CHD, and don’t smoke, here’s what you should aim for (levels are measured in milligrams per deciliter, or mg/dl — a deciliter is about 3 ounces). An optimal LDL level is less than 100 mg/dl. 130-159 mg/dl is borderline high and anything above 160 mg/dl is high.
Everything from your weight to whether or not you smoke to your family health history — even the amount of stress you’re under — affects your LDL level. Of course, your diet makes a difference, too, particularly the types of fats you eat.
High-density lipoproteins, or HDLs, are the good guys — the “garbage trucks” of the bloodstream, as described by C. Noel Bairey Merz, M.D., director of the Preventive and Rehabilitative Cardiac Center at Cedars-Sinai Medical Center in Los Angeles. HDLs typically transport about 20 to 25 percent of the cholesterol in your blood, carrying it away from tissues to your liver, which disposes of it. The more HDL in your bloodstream, the more artery-clogging cholesterol is being removed.
Research finds that for every 1 percent increase in your HDL level, your risk of a heart attack drops 3 to 4 percent. By comparison, a 1 percent drop in your LDL level reduces your risk of a heart attack just 2 percent. HDL is so beneficial that a high level may offer enough protection to cancel out a heart disease risk factor like having diabetes or being overweight.
Having low HDL, on the other hand, often signifies other problems. For instance, many people with low HDL also have high levels of other dangerous blood fats, such as triglycerides and remnant lipoproteins (more on this later). That makes sense, since low HDL means fewer “garbage trucks” disposing of the “trashy” cholesterol. Low HDL can also be a sign of insulin resistance and metabolic syndrome, or Syndrome X.
An HDL level of less than 40 mg/dl is risky, 40-59 mg/dl is average, and 60 mg/dl is protective.
Smoking, being overweight, being sedentary, and consuming a high-carbohydrate diet (more than 60 percent of your calories) contribute to low HDL. So does a family history of low HDL. In fact, about half of HDL imbalances are due to genetics. Women are lucky in that they generally have a higher HDL level than men. But some doctors think women need these higher levels to remain healthy, and they suggest an HDL level even higher than 60 (the usual target) is most desirable for women.
Another up-and-coming indicator of your overall risk of heart disease is your non-HDL cholesterol count. You see, not all “bad” cholesterol is equally bad. While LDL has long been the focus of cholesterol reduction efforts, researchers have recently identified several other lipoproteins, including VLDL and IDL (intermediate-density lipoproteins) that also affect your cardiovascular health. To take these into account, they’ve come up with a new measurement and focus of treatment: non-HDL cholesterol. Your non-HDL cholesterol count is simply your total cholesterol minus HDL, or put another way, the sum of your LDL, VLDL, and IDL.
In late 2002 researchers published an article in Circulation, the journal of the American Heart Association, confirming that if you have heart disease, your non-HDL level can help predict your risk of a heart attack or angina (chest pain) and determine treatments. “LDL cholesterol, even though it is a ‘bad’ cholesterol, tells only part of the story,” said lead author Vera Bittner, M.D., MSPH, professor of medicine in the division of cardiovascular diseases at the University of Alabama at Birmingham. “We found that while LDL cholesterol is important, the non-HDL cholesterol is the more important predictor — at least in this group of people with heart disease.”
Many people won’t know their levels of VLDL and IDL, and that’s okay. Current recommendations call for obtaining at least a total cholesterol and HDL level to determine CHD risk. If these levels don’t raise any red flags, there’s no reason to investigate further (unless you have CHD or a strong family history of heart disease). But if the levels are elevated, you’ll probably need more detailed tests, possibly including VLDL and IDL counts.
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.