Cholesterol: The good, the bad, and the oily

By Tyrone M. Reyes, M.D.

Control your cholesterol.” You’ve probably heard that before, especially if you have some form of heart disease. And while you might know a little about cholesterol — some kinds are good and some are bad, and having too much is definitely not good — you’re not always clear on what the commotion is all about.

So what exactly is cholesterol and how does it work? Why is too much bad for you? Does lowering it really help your heart? These are good questions that are asked not only by patients but by doctors as well. Although quite a bit is known about cholesterol and its relationship with heart disease, much is still uncertain and doctors suspect that the relationship may be more complicated than previously believed.

Here’s what’s known and what’s not about cholesterol.

What is cholesterol?

Cholesterol is a waxy substance found in all of your body cells. Its normal function is to help form and maintain cell membranes, and to protect and insulate nerve fibers. Cholesterol is also involved in the formation of sex hormones, such as estrogen, and the production of bile salts, which help you digest fats.

Your liver produces most of the cholesterol in your body — and all the cholesterol you need. But you can also get cholesterol from foods of animal origin, such as red meat and eggs. Even cholesterol-free foods that are high in saturated fats can contribute to an increase in blood levels of cholesterol. In fact, foods high in saturated fats appear to be one of the main causes of high cholesterol levels.

Good and bad cholesterol

Cholesterol is carried in your blood attached to proteins. This cholesterol-protein package is called lipoprotein. There are two main types of lipoproteins.

• Low-density lipoprotein (LDL). Low-density lipoproteins transport cholesterol throughout your body, delivering cholesterol to different tissues and organs. When the cells have all the cholesterol they need, they reduce the number of receptors, or gateways, for cholesterol to enter. As a result, cholesterol contained in the LDL particles (LDL cholesterol) starts to build up in your blood stream.

Over time, circulating LDL cholesterol undergoes chemical changes (becomes oxidized) and also reduces in size. These smaller particles more easily enter the blood vessel wall and start to build up under the vessel lining. Deposits of LDL cholesterol particles in vessel walls are called plaques and can lead to inflammation, bleeding into the area, and calcium buildup (calcification). Eventually, the buildup of plaques can start to crowd the space within the blood vessel and obstruct the blood flow. This process of plaque accumulation is called atherosclerosis.

When atherosclerosis affects the arteries leading to your heart (coronary arteries), you may have chest pain and other symptoms of coronary artery disease. If plaques tear or rupture, a blood clot may form — blocking the flow of blood or breaking free and plugging an artery downstream. If blood flow to part of the heart stops, you’ll have a heart attack. If blood flow to your brain stops, a stroke occurs. This is why LDL cholesterol is often referred to as “bad” cholesterol.

An optimal level of LDL cholesterol is less than 100 milligrams (mg, a measure of weight) per deciliter of blood (dL, a measure of volume) — a little less than half a cup. LDL levels of 130-158 mg/dL are considered “borderline high,” 160-189 mg/dL are “high,” and 190 mg/dL and above are “very high.”

• High-density lipoprotein (HDL). Rather than deliver cholesterol to cells, high-density lipoproteins leave the liver with very little cholesterol, pick up excess cholesterol on their route through the bloodstream and take it back to your liver. The liver excretes this cholesterol into the bile and out of your body through your bowels. Because HDL particles remove excess cholesterol from your body, they are considered protective. That’s why HDL cholesterol is often referred to as “good” cholesterol (see diagram on Page D-1).

You want higher levels of HDL, ideally 60 mg/dL or greater, according to the US National Heart, Lung, Blood Institutes (NHLBI) National Cholesterol Education Program.

Your “lipoprotein or lipid profile” test, done after a nine to 12-hour fast, will also provide information about triglycerides, another form of fat in your blood. (Watch out for a separate article on triglycerides next month.) Fasting triglyceride levels above 150 mg/dL are considered “borderline high,” and 200 mg/dL or more are “high.”

The quest for lower cholesterol

Originally, scientists thought the main contributor to LDL cholesterol was, logically enough, the cholesterol found in foods, such as meat and eggs. It turns out, however, that only some dietary cholesterol find their way into the bloodstream as serum cholesterol. It’s still a good idea though, especially if you’re at risk for heart disease, to limit intake to less than 300 mg per day. For individuals either with or at high risk of heart disease, the NHLBI’s Therapeutic Lifestyle Changes (TLC) diet calls for consuming less than 200 mg of dietary cholesterol per day. (One egg, for comparison, contains about 175 mg.)

Today, most experts believe the chief LDL cholesterol culprit is saturated fat — found in high amounts in animal products such as meats, full-fat dairy, and butter. Although the connection between saturated fat intake and heart disease risk remains the subject of study, scientists call for limiting saturated fat intake to less than seven percent of your total calories. Switching from saturated to mono or polysaturated fats has been shown to reduce the risk of heart disease (An Apple a Day, New Facts on Fats, October 12, 2010).

You should also avoid trans fats, found in the partially hydrogenated oils used in some baked goods and packaged products, which raise LDL cholesterol. Since these findings about the effects of trans fats, however, they’re much less commonly used than saturated fat.

What about total fat intake? The emphasis has shifted from reducing the quantity of fats of all kinds in your diet to improving the quality of fats. Experts recommend consuming no more than 25 percent to 35 percent of your total calories from fats.

Another dietary change you can try is increasing consumption of soluble fiber. Soluble fiber binds with cholesterol-containing bile and helps carry it out of your body — this is the science behind oat-cereal’s claim to lower cholesterol.

Other steps you can take to control cholesterol, according to the NHLBI’s National Cholesterol Education Program, include losing weight if you’re overweight and getting regular physical activity. Getting 30 minutes of physical activity on most days of the week can help lower LDL and raise HDL; it’s particularly important if you’re overweight and have high triglyceride or low HDL levels.

Overall, according to the NHLBI, the following diet and lifestyle changes can put a big dent in your LDL numbers:

• Reduce saturated fat to less than seven percent of calories: eight to 10 percent LDL reduction.

• Decrease dietary cholesterol to less than 200 mg/day: three to five percent reduction.

• Add five to 10 grams/day of soluble fiber: three to five percent reduction.

• Lose 10 pounds if overweight: five to eight percent reduction.

• If dietary and lifestyle changes aren’t enough, medications are available to help lower LDL levels further. Statins are some of the most popular and effective drugs for lowering LDL cholesterol. These drugs work by directly preventing the formation of cholesterol in the liver. Studies show that statins not only lower LDL cholesterol but also reduce your risk of dying of cardiovascular disease. Other cholesterol-lowering medications are available too, such as resins, fibrates, the B vitamin niacin, and cholesterol absorption inhibitors.

Taking control of your cholesterol with a combination of dietary and lifestyle changes can lower your LDL numbers by as much as 20-30 percent, while increasing your HDL count. Even if you’re taking statins or similar drugs, you can still do more to improve your cholesterol and protect your heart.