Correlation or Causality? Wine and Heart Health

From a lecture series presented by The Great Courses

Is there a link between red wine and heart health, or coffee and heart health? To answer these questions, we must determine whether the connection is one of correlation or causality. Go behind the scenes of popular health articles and learn how to evaluate the results from the actual medical trials.

Stethoscope, red wine and heart image

Health Journalism Reveals More Transparency

Medical science is, by nature, nuanced, but the media tends to oversimplify complex issues in order to gain clicks and views. We’ve seen this when it comes to coffee and its health benefits and risks.

In 2004, headlines in the news included, “Coffee May Raise Heart Disease Risk,” while 2015 had more coffee-positive headlines like, “Drinking Three Cups of Coffee a Day Reduces Risk of Heart Attack.” In both cases, the articles failed to go in-depth on the strengths and weakness of the medical studies being reported on.

More recent articles based on coffee and heart studies illustrate more nuance and honesty. From The Guardian, in July 2017, a headline read: “Coffee Cuts Risk of Dying from Stroke and Heart Disease, Study Suggests,” with a subhead, “Coffee a day keeps the doctor away? Perhaps, but benefits may be down to lifestyles rather than the brew itself.”

This is a transcript from the video series The Skeptic’s Guide to Health, Medicine, and the Media. Watch it now, on The Great Courses Plus.

Here’s a news article about two newer studies that actually looked at the real endpoints, stroke and heart disease, rather than associated factors like blood pressure.

One involved 185,000 people, the other 450,000 people, all of whom were followed for about 16 years, assessing their eating and lifestyle habits, and tracking their rates of cardiovascular and other diseases.

These are still observational studies, but they’re huge, and they cover a long span of years—that makes their conclusions more reliable. And both studies found a decreased risk of serious cardiovascular diseases among the coffee drinkers.

The Guardian article also does a great job outlining the shortcomings of these studies:

“But experts warn that the two studies, both published in the Annals of Internal Medicine, do not show that drinking coffee was behind the overall lower risk, pointing out that it could be that coffee drinkers are healthier in various ways or that those who are unwell drink less coffee. In addition, levels of coffee drinking were self-reported.”

This description is a great example of solid health reporting from the headline on down.

Learn more about how to avoid falling for “clickbait”

Showing Causality in Medical Studies

And, if you needed more convincing, Time.com reported in 2017 about a different study looking at decades of data for 15,000 Americans in the Framingham, Massachusetts, heart study. Their headline was “Here’s Another Reason to Feel Good about Drinking Coffee.”

This study showed a solid dose-response effect of up to six cups of coffee a day, with each cup further decreasing the risk of heart failure, stroke, and coronary artery disease. As mentioned, the only sure way to prove causality is an experimental study.

But sometimes those just cannot be done. So using the quote “weight of the evidence” is second-best. Big observational studies add weight to the evidence, as do trials done on animals, or studies looking at surrogate markers.

Another way to support causality is showing a dose-response relationship. That is, even though this was only an observational study, the data showed that as more and more coffee was consumed, the effect grew larger and larger.

Biologically, this fits the idea that it’s the coffee that is causing the endpoint. Again, not proof, but this dose-response relationship adds to the evidence that coffee itself is preventing cardiovascular disease.

Shifting Views on Coffee and Heart Health

So, to recap the big picture, why did media stories go from coffee is bad for your heart to coffee is good for your heart? Early studies didn’t do a good job separating out or controlling for important variables.

For instance, coffee drinkers tended to be smokers, and it’s the smoking that’s bad for your heart. They were smaller studies, too, and of shorter duration.

They also depended on surrogate markers, and especially early-on surrogate markers that themselves were far removed from the occurrence of actual heart disease. Better studies have provided better insight, and the story of coffee and heart disease has changed.

top view image of table with open notebook and the text new mindset new results

Of course, this might not be the end of the story—we still don’t have good clinical trials, and probably never will. But the weight of the evidence makes it pretty clear that if you’re concerned about cardiovascular health, it’s okay to enjoy that “cup of joe.”

Red Wine and Heart Health: Why the Connection?

In the 1990s, enthusiasm for alcohol consumption—and, specifically, for red wine consumption—was a common theme in media headlines. Some examples: from the UK’s Independent, “To Be Taken with Every Meal: Red Wine Is So Good for You,” and from CNN, a more specific endorsement of one red wine varietal, “Cabernet Sauvignon Called Good for Arteries.”

The primary driver of interest in red wine was what became known as the French Paradox. We knew that compared to most other modern, industrialized countries, France seemed to have a population that experienced fewer heart attacks and less cardiovascular disease.

This was true despite the fact that traditional French cuisine includes plenty of butter and rich sauces. We also know that French people, as a population, drink a lot of red wine.

Now, the first thing that ought to come to mind is—so what? Is there any reason to think that more red wine is really what causes less heart disease?

There are many other differences that could come into play here: other dietary things, genetics, differences in smoking or rates of diabetes or obesity or high blood pressure—lots of things. But, somehow, we kind of got hung up on the red wine.

Learn more about coffee, wine, and cardiovascular health

Critically Evaluating Red Wine’s Health Benefits

To their credit, some news agencies sounded a note of caution. From The New York Times in 1994 came “Wine for the Heart: Overall, Risks May Outweigh Benefits.”

This article talked about some of the real, well-known risks of consuming too much wine, things like alcoholism and liver disease. Overall mortality, when they looked at data from several countries, seemed much higher among people who consumed more than two alcoholic beverages a day.

That’s a very good point: Even if red wine did prevent heart attacks, if it makes you more likely to die of something else, it’s not beneficial. It pays to look at the big picture.

If we fast forward to what we know now, you’ll see the tone of recent headlines has changed. CNN published an excellent long form article in 2015, titled “Health Effects of Red Wine: Where Do We Stand?”

CNN provided great context, including a timeline reviewing what was known about wine from ancient times though today. USA Today has also become more skeptical of the alcohol-and-heart-prevention bandwagon, with its story, “Alcohol Good for Your Heart: Evidence Is Evaporating.”

It turns out, in many much larger studies, that red wine is not superior to other alcoholic drinks. It doesn’t confer any specific cardiovascular protection.

Any alcoholic beverage, when consumed in moderation, might decrease your risk of cardiovascular disease by a modest amount, and might help prevent diabetes, too, though the evidence there is less strong.

However, there are risks. Drinking is associated with a higher risk of several kinds of cancer, and death from drunk driving, and problems with potential addiction, and, well, you get the picture.

That “in moderation” qualifier means one alcoholic drink a day for women, and one or two for men. More than that is not a good idea—health benefits quickly become health dangers when people drink too much.

That’s a real problem with headlines that enthusiastically support the heart benefits of alcohol consumption. They may do more harm than good.

From the lecture series The Skeptic’s Guide to Health, Medicine, and the Media, taught by Professor Roy Benaroch, M.D.

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