Bad Cholesterol Isn't Actually Always Bad

Cholesterol is complicated. While just reading the word conjures images of people eating fast food or clutching their hearts, cholesterol isn't inherently bad. When your levels are under control, it's actually a necessary and helpful part of your internal chemistry.

That's true even for so-called "bad" cholesterol, or the type associated with low-density lipoprotein (LDL) particles, says Michael Blazing, an associate professor of medicine at Duke. "LDL is nothing more than a truck that carries cholesterol around so that any cells that need it can get it," he says.

Brace yourself. Piping hot biochemistry coming your way: Your cells use cholesterol—a fatty substance—to produce hormones, vitamin D, and enzymes that help you digest food. While cells can produce some cholesterol on their own, they may also need to access the cholesterol made and stored in your liver.

That's where LDL comes in. To borrow from Blazing's analogy, LDL is like a truck that transports cholesterol from your liver to the cells of your body via your blood. Meanwhile, high-density lipoprotein (HDL) particles perform the opposite task. They take cholesterol from your cells and haul it back to your liver, which then removes the cholesterol from your blood.

In some cases, LDL-transported cholesterol can accumulate in your arteries and up your risk for serious heart trouble. That's why it's sometimes called "bad" cholesterol. Because HDL is removing cholesterol from your cells and blood, it's known as "good" cholesterol. "But LDL is only bad when it's too high," Blazing says. Defining "too high" is where things get tricky. (Okay, trick-ier.)

As of now, most health authorities recommend people at high risk for heart trouble aim for an LDL count below 70 mg/dL. For healthy young people, the current target is much higher; anything below 160 mg/dL is considered safe—though heart experts are still sorting out the "ideal" numbers to shoot for.

But a just-published study Blazing coauthored suggests a much lower target—below 40 mg/dL—may lead to better outcomes among high-risk patients. It's possible to lower LDL cholesterol by eating right and exercising. But getting your LDL cholesterol below 70—let alone down below 40—usually requires a pharmacological assist from prescription drugs like statins, says Randy Thompson, a cardiologist at St. Luke's Health System in Kansas City.

Thompson just published a paper on a South American people called the Tsimane, who live in the Bolivian Amazon. As a group, the Tsimane have some of the healthiest hearts ever discovered. Compared to the heart of an average American adult, the heart of a Tsimane is 28 years younger (based on biomarkers of arterial disease), Thompson says.

What does a Tsimane's cholesterol look like? "Their lifelong LDL is around 70," Thompson explains. These are people who eat almost nothing they don't grow, hunt, or gather themselves, and who spend nearly every waking hour on their feet and engaged in some form of physical activity. If they're bottoming out around 70, you can see why going much lower would be tough for most of us without the help of drugs.

So is zero LDL cholesterol achievable—or even desirable? Yes and no, says Robert Rosenson, director of cardiometabolic disorders at the Icahn School of Medicine at Mount Sinai. Some people are born with an inherited blood disorder that deprives them of nearly all LDL. While they may not have to worry much about arterial disease, they may suffer from night blindness, bone fractures, bleeding problems, and other not-fun health issues, Rosenson says.

For those without that genetic abnormality, it may be possible to get LDL down to 25 mg/dL or below using a class of drugs called PCSK9 inhibitors, Rosenson says. He's published research on the benefits of this kind of aggressive LDL lowering—which may include lower risks for stroke and heart disease. His research has also turned up few negative side effects.

"But you wouldn't do this for someone at low-risk for cardiovascular disease or stroke," he says. The drugs are expensive, and there's not a big enough payoff for someone who's already at low risk for heart problems. So to sum all this up, even so-called bad cholesterol is only bad in certain situations. You don't want too much of the stuff circulating through your blood. But at safe levels—and especially if you're young and healthy—LDL isn't your enemy.

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