Blueberries are often in the news as a potential cure-all for virtually every health condition. Whether it’s diabetes, heart disease, obesity, or even cancer, blueberries have been promoted as a treatment or even cure for almost every disease under the sun.
It’s impossible to know why this is — Maybe it’s because they’re delicious, maybe it’s because they are expensive and slightly mysterious, or maybe it’s because there’s a large research institute funded by the U.S. Highbush Blueberry Council (an industry group)that pumps out a remarkable number of trials demonstrating that blueberries are linked to good health.
Who knows? It could be all of the above.
The latest news is no exception. According to every media outlet from Forbes to the Express to the New York Times, eating just a punnet of blueberries a day is lifesaving. The magical fruit won’t just make you feel better — apparently, just a few blueberries a day will reduce your risk of heart disease by 15%!
It sounds amazing. Too bad it’s total nonsense.
Blueberries won’t do anything at all to help your heart health.
The recent study that has blueberries being hailed as the cure for all heart problems was a randomized-controlled trial looking at the effects of blueberries on heart health. The researchers split people into three groups, gave two groups either a little or a lot of frozen blueberry powder, and gave one group a placebo control which was flavoured sugar powder.
Now, normally this is the bit of the blog where I’d tell you the findings and then debunk the results. But, in all honestly, I think this was a pretty good study. There were a reasonable — if slightly small — number of participants involved, it was long enough to detect an effect, and the statistical analysis was reasonable and fair.
Which is why, when I say that blueberries don’t have any heart health benefits, you can trust me, because that’s exactly what the study found. People who took the blueberry supplements didn’t improve on any of the primary markers of heart health compared to placebo, which means that, based on this research, it’s unlikely that blueberries confer any benefit to heart health at all.
Which is exactly the opposite of what most news stories reported.
So how did the story get so muddled? Well, it turns out that there were some significant results. In a smaller subgroup analysis of the trial results, there were barely-significant (p=0.04) associations between people who had the highest dose of frozen blueberry powder and arterial stiffness, which was one of the secondary surrogate outcomes the trial looked at. There was also a very modest improvement in one type of cholesterol in an even smaller group of people, once more than half of the trial participants were excluded.
And this was what the trial focused on.
The problem is that, if you flip a coin enough times, you will almost always get at least one heads. Similarly, if you do enough statistical tests, you’ll probably find at least one positive result. And this study did a lot of tests. Here’s the main table of results:
From these results we can say that blueberries probably don’t help with:
- Blood pressure
- Blood sugar
On the other hand, there may be a very small benefit in terms of arterial stiffness from blueberries, although since a smaller intake of blueberries actually made this worse it’s extremely unlikely that this is the case. It looks much more likely that, based on the results of this trial, blueberries do nothing whatsoever for heart health.
The problem is that the scientists did not report the study this way. They focused entirely on the very minor benefits from a secondary surrogate outcome and ignored completely the negative results for the vast majority of things they looked at.
And that’s what ended up being reported on.
So, what to make of these results? Firstly, every single media story that reported a 13% or 15% benefit to the risk to heart disease was completely and utterly wrong. This study didn’t look specifically at heart disease at all, just surrogate markers of the disease that may or may not be directly related. The 15% figure came from a vague extrapolation that might not have any relationship with actual outcomes.
But more importantly, the study didn’t show any benefits at all. Despite the reporting, and the conclusions of the study itself, there didn’t appear to be any benefits to heart health from blueberries, which actually lines up quite well with previous research.
Why did this study report such positive results despite not finding anything much? Well, we could speculate. There are many possible reasons. One potential cause could be that the funder, who also appear to employ two of the lead authors of the study — the Highbush Blueberry Council — had some influence, although it’s impossible to tell.
Maybe I’m just being cynical.
Whatever the reason, the study was reported entirely wrong. Based on this and previous research, blueberries are almost certainly a waste of time for heart disease.
Eat blueberries because they’re tasty. They’re an expensive but delicious snack. Replacing less healthy snack foods — say, chocolate, or chips — with blueberries is probably going to be good for you regardless of the independent benefits that blueberry anthocyanins might have.
But don’t gorge on this lovely fruit because it’s going to cure your heart disease.
The evidence shows that it’s probably a total waste of time.
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