Blueberries are a perennial favorite in the news cycle. Maybe it’s because they are one of the more expensive berries — and we all know more expensive means better for your health — or maybe it’s just that they taste great in a banana smoothie. Whatever the reason, hardly a week goes by without someone mentioning this photogenic fruit, with media sources claiming that blueberries can prevent cancer, make you lose weight, and of course prevent aging and make you live forever.
Unfortunately, as is often the case, the story is a lot more complex than that. Blueberries may be a tasty — and relatively healthy — treat, and certainly can be part of a healthy diet.
But do they treat heart disease? The evidence suggests no.
Don’t go off your meds and start pounding punnets just yet.
The recent ‘study’ that has generated such sensationalist headlines is actually what’s known as a narrative review. Basically, the authors have compiled a series of experiments that they have been involved in to make a case for blueberries being helpful for heart disease. In many ways, it’s like an essay — they’ve collected a specific set of studies, and put them into order to tell a story.
The researchers collected a series of 2 human and 1 animal study that looked at the effects of a specific type of molecule contained in blueberries — called anthocyanins — on flow-mediated vasodilation, and two studies that looked at people who drank a blueberry supplement equivalent to 200 grams of blueberries per day on the same outcome. They found that anthocyanins improved flow-mediated vasodilation by a bit, that taking blueberry supplements increased the amount of anthocyanins in the blood, and that the blueberry extract also increased vasodilation in people by a bit when taken for a month.
If that sounds quite complex, that’s because it is. If it sounds like it has almost nothing at all to do with heart disease, that’s because it probably doesn’t.
Let me explain.
Flow-mediated vasodilation is what’s known as a surrogate outcome. The idea of surrogate outcomes is that it can be very hard to measure disease states — say, heart attacks — because they don’t happen very often. They can also be very expensive or difficult to determine. So instead we measure things that indicate the risk of a disease, because otherwise we can’t study the issue at hand. For example, in diabetes trials we usually measure blood sugar levels, because diabetes issues can take years or even decades to detect, but blood sugar gives you a good idea of long-term diabetes risk and can be measured easily with a blood test.
The problem with surrogate outcomes is that they are only ever an approximation, and they can be very misleading. Improving a marker for heart disease is not the same as improving heart disease itself. So while there is some evidence that flow-mediated vasodilation can impact the risk of developing issues like high blood pressure, and this can cause heart attacks, the connection is not as solid as you might think. A study that relies only on a surrogate outcome like flow-mediated vasodilation to demonstrate an effect might not prove much in terms of benefit at all.
The researchers did also look at blood pressure, which is good, but only found a very marginally significant association for one measurement of blood pressure, which is not so good. This slight improvement was the one that caused the amazingly absurd “blueberries are as good as heart medication” headlines.
It’s also worth noting that these were extremely small studies. The sample size ranged from 5 to 40 total participants, which is really not a lot for this kind of trial. It’s hard to know what to make of the findings when there were so few people studied.
The study also didn’t find an improvement in any of the other factors they looked at, including cholesterol levels, blood sugars, and blood cell counts. The participants in the study were also taking a lot of blueberries — remember, equal to 200 grams a day. That’s about $120 of blueberries a month, which is quite a lot of fruit.
So, overall, a big benefit for a very loosely-connected surrogate outcome for heart disease, and not much benefit for anything else, in a series of tiny trials using very high doses of the treatment in question.
Not quite as peachy a picture as the media stories suggest.
This brings us to the funniest part of the whole story. You see, at this point you might well ask: who funds research into blueberries? What’s the point? There’s not likely to be an enormous clinical benefit from a little bit of fruit, so who is interested in funding this really quite expensive work?
It turns out that it’s the Wild Blueberry Association of North America.
Now, funding isn’t everything, and industry funding can and does make a difference in clinical research. But it’s impossible not to feel a bit skeptical about a tiny trial — or series of them — that was funded by the blueberry growing industry and found that blueberries improved health.
It’s even more problematic when you look at the literature for blueberries more broadly. A recent systematic review that looked at a total of six studies with 204 participants found that there was no benefit for blueberries in heart disease. Based on the other studies done in this area, it seems likely that blueberries have no benefit to heart health at all, despite the headlines.
Bottom line? Fruit is good for your health. Eating more fruit is almost always going to improve your diet.
Blueberries are fruit. Therefore, eating more blueberries — and less junk — will usually be a good thing for you.
But this is true of almost all fruit out there. You could eat more apples, durians, rambutans, starfruit or pears. You could go to town on some lychees, or try some dragonfruit instead.
If you’re worried about your heart health, talk to a doctor. Never stop taking any medication before talking to your doctor, especially based on sensationalist articles. Blueberries aren’t going to replace your heart pills any time soon.
Ultimately, there’s no good reason to think that blueberries are any more helpful for your health than other fruit.
They certainly aren’t going to save your life.