The Great Courses are for Great Learners—Like You!

Never stop learning with The Great Courses Plus! Stream over 11,500 video and audio lectures, delivered by experts from the world's most respected institutions. For a limited time, get a FREE MONTH trial!

The Great Courses are for Great Learners—Like You!

Never stop learning with The Great Courses Plus! Stream over 11,500 video and audio lectures, delivered by experts from the world's most respected institutions. For a limited time, get a FREE MONTH trial!

Is Coffee Bad for Your Heart? The Facts Behind the Headlines

It’s a common question that many coffee drinkers have considered—”Is coffee bad for my heart”? The answer can be complicated. Comparing popular media opinion to actual evidence from medical trials reveals the truth behind coffee’s health risks and rewards.

coffee beans and a stethoscope
Image: aroonroj/Shutterstock

Coffee and Heart Health

A 2002 WebMD.com headline read “Is Caffeine Bad for Your Heart?” with a subtitle “New research suggests caffeine elevates blood pressure, stress.”

The story itself is about a study that looked at blood pressure and other measurements in a small number of coffee drinkers—47 adults. Over three days, the study participants were given either a capsule of caffeine equivalent to about four cups of coffee or a capsule of placebo; on the other day, they received the other capsule.

When participants serve as their own controls, it is often called a crossover study. The researchers found that on the caffeine day, average blood pressures were higher by about three or four points, going from (just for example) 120/80 to 124/83.

At the same time, the average heart rate actually decreased by two beats per minute—a finding that was largely ignored in the press, but that reflects decreased stress on the heart. The article says, “The researchers concluded that the equivalent of four cups of coffee raises blood pressure for many hours. Although the increases appear modest, they are large enough to affect heart attack and stroke risk.”

What do you think? Are you convinced that coffee is bad for your heart? The answer is complicated. Even what is known now isn’t based on rock-solid evidence.

First, the study was quite small, involving all of 47 people. Small studies are not strong studies.

Second, it only documented one day of very modestly increased blood pressure. When we talk about the increased risk of heart disease related to high blood pressure, we’re talking about a risk that develops over many, many years.

One day of higher blood pressure honestly doesn’t matter. What could matter is years and years of high blood pressure, but that’s not what was measured in this study.

We don’t know that caffeine raises blood pressure on day two or seven or 100 of coffee drinking, or much less after 10 years of coffee drinking.

image of heart on top of coffee beans
Image: Shutterstock

Dr. Benaroch’s course, The Skeptic’s Guide to Health, Medicine, and the Media helps you uncover the facts about prevalent health myths we just can’t get away from. Check it out on The Great Courses Plus, where it’s one of many courses on topics including integrative medicine, emergency medicine, and mind-body medicine. And if you’re a new subscriber, you’ll get an entire month of unlimited access for free.

Heart Health or Blood Pressure: What’s Actually Being Measured?

But most importantly, this study looked at what’s called a surrogate marker rather than a real clinical endpoint. The headline of the story was “Is Caffeine Good for Your Heart?” but to be more honest, the study was all about a measurement called blood pressure.

They weren’t looking at heart damage or heart disease. Now, we do know that over time, a long period of hypertension, or an elevated blood pressure, is a risk factor for heart disease.

But they’re not one and the same. Not everyone with high blood pressure gets heart disease, and not everyone with heart disease has high blood pressure.

It may be an important observation that caffeine elevates blood pressure. But showing the rise in blood pressure is not the same as showing that caffeine raises the risk of heart disease or death, or anything that’s significantly important.

Another Coffee Study Misses the Big Picture

Here’s another headline about coffee and heart health, again from WebMD, this one from 2004: “Coffee May Raise Heart Disease Risk.” The article is about a study done in Greece involving over 3,000 adults—that’s much bigger than the 2002 study of 47 adults, so that’s a good start.

The participants, none of whom had any history of heart disease, were asked about how many cups of what kinds of coffee they drank, and blood was drawn to test for what are called “markers of inflammation.” These are blood tests that show that some kind of inflammatory process is underway, and previous research had shown that these markers correlate with heart disease risk.

And they did find that the more caffeine consumed from coffee, the higher these markers turned out to be. The conclusion from the article was, “Drinking even moderate amounts of coffee may raise your risk of heart disease.”

The article and the headline didn’t make it clear, but this was another surrogate marker study. The study didn’t examine if the participants developed heart disease; it only measured these inflammatory markers.

Though the inflammatory markers indicate a risk factor, they’re only one of many risk factors. Maybe the coffee also helped the participants lose weight, which would be a marker for improved heart health.

Or maybe coffee prevented diabetes, also helping the heart. Or maybe coffee drinkers were less likely to overindulge in alcohol—and that would protect the heart, too.

Conversely, maybe coffee increases alcohol consumption. We just don’t know from this study.

There’s another problem with this study that wasn’t mentioned in the news article. It’s subtle, but it’s important: The participants were asked to remember what kind of coffee they consumed, and how much, and how often.

Did they remember correctly? Could it be that some over- or underestimated their consumption? That is pretty likely.

Studies that rely on subjects remembering what they’ve done are weaker than studies that collect data as it happens, by having people fill out a daily diary, or even better, by using an electronic device to count how often they use their coffee machines.

Though imperfect, the evidence as of 2004 was stacking up on the anti-coffee side. These studies of surrogate markers drove headlines and created a media impression that coffee of any kind was bad for your heart.

Thankfully, for us lovers of coffee, more scientifically rigorous studies appear to be tipping the scales in the our direction. While the scientific consensus may still be out, this bean isn’t going away any time soon.

If you want to learn more about the facts behind the headlines in today’s media coverage of health and medicine, we suggest The Skeptic’s Guide to Health, Medicine, and the Media. Lecture ten covers how coffee and wine affect your heart in-depth. You can stream the entire course for free with a month-long free trial of The Great Courses Plus.