关于咖啡的健康影响，终于有了篇严谨的研究｜科学60秒

Tanya Lewis: Today we’re talking about coffee. We hear a lot of conflicting findings about whether our favorite beverage is good or bad for our health. But recently, an especially rigorous study came out that may finally answer some of our percolating questions.

Josh Fischman: There’s a good chance that, right now, you’re sipping the very thing we’re talking about. Coffee. It is one of the most widely consumed beverages in the world.

Lewis: It’s true. Here in the U.S., the average person drank almost 89 gallons of coffee in 2016—more than soda, tea and juice combined.

Fischman: That’s a lot of java. Or joe, brew, or jitter juice, whatever you like to call it.

Lewis: Indeed. Do you drink coffee, Josh?

Fischman: Actually I guess I’m one of the few people who doesn’t. I used to guzzle it, though—about 4 or 5 cups a day. But I gave it up a few years ago.

Lewis: Why? What happened?

Fischman: Honestly, my stomach started getting upset. I figured I could do without so much acid, you know?

Lewis: That totally makes sense. 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 that up.

Fischman: There are times when I catch the aroma from a coffee shop, and it just smells so good!

But listen, I’m still not sure coffee was causing my problems. It feels like every day there’s a new study telling us coffee is good for us or bad for us, for a whole bunch of different reasons. With all these conflicting messages, it can feel like whiplash.

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

Most nutrition studies are observational studies, which compare health outcomes in people who happen to drink coffee to those who don’t. But it’s impossible to rule out other variables that could affect what you’re trying to measure.

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

Fischman: So, what’s 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 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 didn’t, he set up a randomized trial to study coffee’s impact on your heartbeat.

They were looking for abnormal heart rhythms called arrhythmias.

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

Lewis: In their new study, Marcus and his colleagues randomly assigned 100 people to either drink or not drink coffee each day for a period of two weeks.

Marcus: And they receive these instructions via text message, and they were randomly assigned to either go ahead and drink all the coffee you want, versus on other random days, avoid all caffeine today.

Lewis: They had participants wear a heart monitor, a FitBit and a continuous glucose monitor. They also had them download an app on their phone that collected GPS location data so the researchers could see when people were actually visiting coffee shops.

Fischman: 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.

Marcus: It's very common for everyone to have an early beat arising from the upper chambers of the heart called premature atrial contractions, or PACs, once in a while.

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

Marcus: Premature ventricular contractions are early beats that arise from the lower chambers of the heart. Again, we all have those sometimes, but those with more are at higher risk of developing heart failure or a weakening of the heart.

Lewis: They found that drinking coffee did not result in more premature atrial contractions—the early heart beats associated with atrial fibrillation. That’s good news for people who were worried about that.

Fischman: That’s good to know. What about the other bad beats, the premature contractions in the heart’s lower chambers?

Lewis: Those were slightly more common on days when people were told to drink coffee, or on days when they drank more coffee—but not enough to be really worrisome.

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

Marcus: On days randomized to coffee, people took on average about 1000 more steps, which is highly significant. And in fact, that difference in average steps has been associated with the improved longevity in large epidemiologic studies.

Lewis: The study couldn’t show why people increased their steps on days when they drank coffee. Maybe they were just walking to the coffee shop or the bathroom more! But regardless, an extra 1,000 steps per day has been linked to a six to 15 percent lower risk of death in other studies.

Fischman: So coffee might actually make people perk up and move around.

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