Good news for coffee lovers

by The Insights

Tanya Lewis: Hi and welcome to Your health, quicklyA American Scientist podcast series!

Josh Fishman: On this show, we highlight the latest life-saving health news, discoveries that affect your body and mind.

Each episode, we dive into a topic. We discuss diseases, treatments and some controversies.

Lewis: And we demystify medical research so you can stay healthy.

I am Tanya Lewis.

fisherman : I am Josh Fischman.

Lewis: Were American Scientist‘s Health Editors.

Today we are talking about coffee. We hear a lot of conflicting conclusions about whether our favorite beverage is good or bad for our health. But recently, a particularly rigorous study came out that might finally answer some of our percolating questions.

[Clip: Show theme music]

[Clips: (sound effects) coffee grinder, coffee percolating, liquid pour, sip]

fisherman : Chances are right now you’re sipping exactly what we’re talking about. Coffee. It is one of the most consumed drinks in the world.

Lewis: It’s true. In the United States, the average person drank almost 89 gallons of coffee in 2016, more than soda, tea and juice combined.

fisherman : That’s a lot of java. Or joe, brew or jitter juice, call it what you want.

Lewis: In effect. Do you drink coffee, Josh?

fisherman : In fact, I guess I’m one of the few people who doesn’t. I used to swallow it, however, about 4 or 5 cups a day. But I gave up a few years ago.

lewis: For what? What happened?

fisherman : Honestly, my stomach started turning. I thought I could do without that much acid, you know?

Lewis: It is quite logical. But personally, I’m not really functional until I’ve had my morning cup of coffee, and I don’t know if I could give it up.

fisherman : There are times when I catch the aroma of coffee, and it smells so good!

But listen, I’m still not sure the coffee was provoking my problems. I feel like every day a new study tells us that coffee is good or bad for us, for a whole bunch of different reasons. With all these mixed messages, it can feel like a boost.

Lewis: Well, it turns out that it’s actually very difficult to study how coffee or any other food or drink affects our health.

Most nutritional studies are observational studies, which compare the health outcomes of people who drink coffee to those who don’t. But it’s impossible to exclude other variables that might affect what you’re trying to measure.

Plus, you have to rely on people reporting what they consumed weeks or months after drinking it. And most of us don’t even remember what we ate for breakfast.

fisherman : So what is the solution ? Is there another way to study this?

Lewis: Well, there is a way to be more objective. I talked to…

Gregory Marcus: Gregory Marcus, professor of medicine and cardiologist at the University of California, San Francisco.

lewis: Marcus and his colleagues took a different approach than most other coffee studies. Instead of just studying people who drank coffee or not, he set up a random trial to study the impact of coffee on your heart rate.

They were looking for abnormal heart rhythms called arrhythmias.

Mark: The subject comes up very frequently in my clinic, where patients suffering from various arrhythmias ask if they can consume coffee. There is this conventional wisdom that coffee increases the risk of heart rhythm disturbances or heart electrical problems, which is my clinical subspecialty. And yet, we and others have generally failed to find a clear association between coffee and arrhythmias.

Lewis: In their new study, Marcus and his colleagues randomly assigned 100 people to drink or not drink coffee every day for a two-week period.

Mark: And they’re texting these instructions, and they’ve been randomly assigned to go ahead and drink all the coffee you want, compared to other random days, avoid all caffeine today.

Lewis: They asked participants to wear a heart monitor, a FitBit, and a continuous blood sugar monitor. They also asked them to download an app to their phones that collected GPS location data so researchers could see when people were actually visiting the cafes.

fisherman : With the heart monitors, what were they looking at?

Lewis: They were measuring two things: the number of what are called premature atrial contractions and premature ventricular contractions.

Mark: It’s very common for everyone to have a premature beat coming from the upper chambers of the heart called premature atrial contractions, or PACs, from time to time.

Lewis: But research has shown that having too much of these beats puts you at risk for atrial fibrillation, which is a dangerously irregular and rapid heartbeat. This is associated with a very high risk of stroke, dementia and death. Then there is the other type of irregular heartbeat:

Mark: Premature ventricular contractions are early beats that come from the lower chambers of the heart. Again, we all have them sometimes, but those who have more of them are at greater risk of developing heart failure or a weakening of the heart.

Lewis: They found that drinking coffee did not lead to more premature atrial contractions, the early heartbeats associated with atrial fibrillation. This is good news for those who were worried about it.

fisherman : It’s good to know. What about the other bad beats, the premature contractions of the lower chambers of the heart?

Lewis: These were slightly more frequent on days when people had to drink coffee, or on days when they drank more coffee, but not enough to be really concerning.

And that’s not all they found. Coffee consumption was also associated with a higher number of daily steps. The days when people drank coffee – and the more coffee they drank – the more steps they took.

Mark: On randomized coffee days, people took an average of about 1000 extra steps, which is very significant. And in fact, this difference in average milestones has been associated with improved longevity in large epidemiological studies.

Lewis: The study could not show why people increased their steps on days when they drank coffee. Maybe they were just walking to the cafe or the bathroom anymore! But regardless, 1,000 extra steps per day have been associated with a 6-15% lower risk of death in other studies.

fisherman : So the coffee might actually make people straighten up and move around.

Lewis: Yes, I guess coffee drinkers were full of beans. But there was a downside to drinking coffee, and it probably won’t surprise you.

fisherman : Ummm, let me guess. Have people slept less?

Lewis: Bingo. Study participants slept about half an hour less on average on days they drank coffee compared to days they didn’t.

But the results varied a lot from person to person depending on whether they were fast or slow coffee metabolizers, which is determined by your genetics.

The researchers gave the participants a saliva genetic test to determine what type of coffee metabolizer they were.

Mark: Thus, the fast caffeine metabolizers actually showed no significant relationship between coffee consumption and sleep, while the poor caffeine metabolizers had the worst effects on sleep. In fact, poor caffeine metabolizers slept on average almost an hour less when exposed to coffee.

fisherman : I never had a problem sleeping when I drank a lot of coffee. But I wake up at a ridiculously early morning – I talk at 5 am – so I’m usually zoned out at 10 pm anyway.

Lewis: I don’t usually find coffee keeping me awake at night, but I try not to take caffeine after about 3 or 4 p.m. Still, this study makes me wonder if I should stop drinking it earlier in the day.

Mark: If someone is suffering from insomnia, we found here in a randomized trial that there are significant effects on sleep – to such a degree that it should really motivate a good trial of coffee to really try to combat the ‘insomnia.

fisherman : Ok, this part is pretty much a no-brainer. But overall, the study seems like pretty positive news for those who enjoy their beer.

Lewis: Yeah, that’s pretty good news. It confirms other observational studies that did not show a higher risk of cardiac arrhythmias.

And some studies have shown that coffee consumption is linked to a lower overall risk of diabetes and lifelong death, which could be the result of the higher activity levels that coffee consumption could produce.

Ultimately, there may not be a simple answer to whether coffee is good or bad for you. It depends on how much you consume and each person is different.

Mark: I think overall this data should be generally reassuring about the safety of coffee. I think one of the challenges in doing nutrition-based research is that there tends to be a kind of natural hunger, especially from the media, but I think that’s just nature human to know to conclude, okay, is it good for me? Or is it bad for me? Which is it? It’s one or the other. And the reality is that the effects of coffee are complicated.

Lewis: Coffee affects each person differently. So if drinking it makes you feel bad, skip it. But if, like me, you enjoy it in moderation, go ahead and have that latte!

fisherman: Your health, fast is produced and edited by Kelso Harper, Tulika Bose and Jeff DelViscio. Our music is composed by Dominic Smith.

Lewis: Our show is part of American Scientistthe podcast of, Science, fast. You can subscribe wherever you get your podcasts.

fisherman: And don’t forget to go to for up-to-date and detailed health information.

lewis: I’m Tanya Lewis.

fisherman : I am Josh Fischman.

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

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