Tanya Lewis: Hi, and welcome to Your Health, Quickly, a Scientific American podcast series!

Josh Fischman: On this show, we highlight the latest vital health news, discoveries that affect your body and your mind.  

Every episode, we dive into one topic. We discuss diseases, treatments, and some controversies. 

Lewis: And we demystify the medical research in ways you can use to stay healthy. 

I’m Tanya Lewis.

Fischman: I’m Josh Fischman.

Lewis: We’re Scientific American’s senior health editors. 

On the show today, we’ve got some surprising news about cholesterol. The so-called “good” kind is supposed to protect your heart and arteries. But it actually makes things worse under certain circumstances. And doctors are just figuring this out. 

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Fischman: You go to the doctor for an annual checkup, right, Tanya? 

Lewis: Sure. As any good health editor would!

Fischman: Me too. You get asked a bunch of personal questions, a cold stethoscope on your skin, and the doctor draws some blood for standard lab tests. Among those tests, when you get them back, are two cholesterol numbers.

Lewis: Right. One is your level of low-density lipoprotein cholesterol, or LDL. It’s supposed to stay under 130 milligrams per deciliter—the lower the better. 

The other one is high-density lipoprotein, or HDL. And that’s supposed to stay above 40 milligrams per deciliter. The higher it is, the better, we’re told.

Fischman: That’s because LDL is the “bad” cholesterol, the one that leads to artery-clogging plaques, heart disease, strokes, and other nasty stuff. We want less of it. 

HDL, on the other hand, is “good” cholesterol. We want more of it.

Lewis: HDL has this good reputation because it binds to LDL, carrying that bad stuff to the liver. From there it gets flushed out of your body, where it can’t hurt you.

Fischman: But … you know that old saying about having too much of a good thing? It seems to be true of good cholesterol. 

Lewis: So, is it possible to have too much HDL?

Fischman: It is totally possible. Turns out that too much HDL actually raises the chances of artery and heart disease, the very things we’re trying to avoid. 

Once you get above 80 for men and 100 for women—and I’m going to stop saying milligrams per deciliter because it’s a mouthful—you’re in the danger zone. A bunch of recent studies have found this effect.

But generally, that’s not what doctors have told patients.

Quyyumi: The teaching has been up until recently, that the higher the HDL, the lower the risk. So traditionally, physicians have been using very high HDL levels as a marker of a really healthy cholesterol profile.

Fischman: That’s the researcher behind some of the newer studies.

Quyyumi: My name is Arshed Quyyumi. I'm professor of medicine in the Division of Cardiology at Emory University School of Medicine in Atlanta, Georgia. 

Fischman: He did a study of more than 400,000 people in the U.K., people without other predisposing risk factors for heart disease. For men, cardiac and other disease risks went up if their HDL levels were under 40—or over 80. For women, the risk climbed once HDL levels topped 100.

Lewis: When you say “climbed,” how much of a risk are we talking about? A few small percentage points, or a much bigger increase?

Fischman:  Excellent question, and I asked Quyyumi about the amount of extra risk that people faced.

Quyummi: If you just took them without any other evaluation of other risk factors like LDL cholesterol, blood pressure, diabetes, etc, it's almost two fold higher compared to the lowest risk group, which would have levels between 40 to 60. 

Fischman: Even when he and his team took into account those other factors, those with very high HDL had a risk that was 80 percent higher than normal. 

Other studies back this up. One of them looked at more than 11,000 people with high blood pressure. It found a much higher rate of cardiovascular problems in people with HDL levels both under 40 and over 80.  

Lewis: OK, let me run through the numbers. HDL is bad if it’s under 40. It’s good if its 40 to 60. Possibly a risk in the 60 to 80 range. And a pretty big risk if its above 80 for men and 100 for women. 

Fischman: Yep. “Good cholesterol” is really bad cholesterol over 80 or over 100, depending on your sex, and under 40. The middle zone is the safe zone.

Now it’s a bit of a mystery why HDL should turn bad when it goes really high. Why should a molecule help you at level 45, for instance, but hurt you at level 85? It’s possible that the shape of the molecules change. So they don’t latch on tightly to circulating cholesterol and help ferry it out of the body. 

Lewis: Interesting. I want to go back to something intriguing you mentioned: There’s a difference between where men and women enter the HDL danger zone. You said it was over 80 for men, but over 100 for women. Why is that?

Fischman: You’re right. There was a 20 point difference between men and women. And honestly, neither Quyyumi’s team nor anyone else really knows why.

Quyyumi: Part of it is thought to be just sex hormone differences, you know, estrogen, testosterone differences…. between men and women. There are some genetic reasons for that as well. It’s not really well worked out.

Lewis: I’ve read that estrogen can increase HDL in women, and that it can be protective. But once women reach menopause, their estrogen levels drop, and HDL becomes less protective. 

In any event, it sounds like women shouldn’t freak out if their HDL is slightly over 80, according to these studies. Though men in that range should be aware they are at risk.

Fischman: Yeah. And there shouldn’t be a huge number of people freaking out, period. Overall, the research shows that about 7 percent of the general population reaches these scary high HDL levels. 

But still, that’s nothing to ignore. If a doctor sees 100 patients in a week, 7 of them will be in this HDL danger zone.

Lewis: If people are in the danger zone, what should they do?

Fischman: I asked Quyyumi about that one, too. Drinking a lot of alcohol drives HDL up, so he’d tell patients guzzling one or two glasses of wine or booze daily to cut it out. 

There aren’t drugs that bring down high HDL. So the big thing he’d do is focus on treating LDL. 

Statins, for instance, are very effective at lowering LDL levels, and he’d use those. 

And baby aspirin, used carefully, can reduce blood clots that lead to heart attacks. Check with your doctor on that one—aspirin can have side effects. 

And there’s one more thing…

Quyyumi: If they're sedentary, they should be encouraged to exercise. Exercise is helpful for everything.

Lewis: I guess I’m going to keep going for my morning runs. And I’ll try to keep my “bad” cholesterol low and “good” cholesterol in that happy middle zone.

Fischman: Our colleague Lydia Denworth calls it the Goldilocks zone: not too low or too high, but just right. You can read her new Science of Health column on HDL in the middle of May, on sciam.com. 

And now I’m going to call my doctor to schedule my yearly checkup.

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Fischman: Your Health Quickly is produced and edited by Tulika Bose, Jeff DelViscio, Kelso Harper,  and Alexa Lim. Our music is composed by Dominic Smith.

Lewis: Our show is a part of Scientific American’s podcast, Science, Quickly. You can subscribe wherever you get your podcasts.

Fischman: And don’t forget to go to Sciam.com for updated and in-depth health news. 

Lewis: I’m Tanya Lewis.

Fischman: I’m Josh Fischman.

Lewis: We’ll be back in two weeks. Thanks for listening!