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I’ve been ignoring cherry juice for well over a decade now. The studies keep showing up in my dragnet of potentially interesting research, suggesting that tart cherries accelerate post-exercise recovery, funded more often than not by the Cherry Marketing Institute. But other studies find no benefit. And more generally, my approach to supplement research is to assume that (a) nothing works and, (b) if something actually does work in any meaningful way, you won’t have to go digging for evidence because everybody will be talking about it.
Cherry juice still hasn’t reached the “everyone is talking about it” stage, at least in my circles, but the studies keep on coming, including a couple of recent reviews and meta-analyses. Interestingly, the gist of some of these recent papers is less “Does cherry juice work?” and more “We know cherry juice works, so why aren’t more athletes using it?” With that in mind, I’m going to try to sum up the current state of research, then offer a few thoughts about why athletes might — and perhaps should — remain hesitant.
The best place to start is a meta-analysis published last year in the International Journal of Sport Nutrition & Exercise Metabolism by Jessica Hill of St. Mary’s University and her colleagues. Hill’s team combined the results of 14 studies with a total of 303 subjects, looking at recovery from strenuous exercise. They found evidence of a “small beneficial effect” on muscle soreness, a “moderate beneficial effect” on recovery of muscle strength, and mixed effects on blood markers of muscle damage and inflammation.
This sounds pretty good. But if you wade into the results of the individual studies, you find a lot of results clustering around zero and a few outliers — generally the ones with the biggest error bars — skewing strongly positive. It doesn’t fill me with a ton of confidence.
Here’s an illustration of what I mean. This is called a “forest plot,” with each individual study outcome represented by a horizontal line, and the overall average shown by a diamond. Lines or diamonds to the left of the vertical line indicate that cherry juice helped strength recovery after damaging exercise; lines or diamonds to the right indicate the opposite. The wider the horizontal line, the bigger the error bar. The studies at the top focus on “metabolic” exercise like endurance cycling; the studies at the bottom focus on “mechanical” exercise like lifting heavy weights. I realize this sounds overcomplicated, but it’s a great way of getting a big-picture view of an entire body of research:
Again, this was the data for strength recovery, which had the most positive effect of all outcome variables in the meta-analysis. What jumps out at me is four strongly positive studies—which, when you look closely, turns out to be one single study by Connolly in 2006, with four outcomes measured at 24, 48, 72, and 96 hours. Remove that study, and I suspect that the “moderately beneficial” overall effects would largely fade away. (And yes, for the record, the Connolly study was funded by Cherrypharm, a tart cherry juice company, and the study’s three authors each had an equity stake in the company.)
So, to sum up, this meta-analysis didn’t eliminate my skepticism when it was published last year. What caught my eye, instead, was a more recent review in the Scandinavian Journal of Medicine & Science in Sports by Malachy McHugh of the Nicholas Institute of Sports Medicine and Athletic Trauma in New York (and, it turns out, a co-author of the 2006 Connolly study).
McHugh’s article offers a great overview of the arc of tart cherry research. Why, for example, is the focus on tart cherries rather than sweet ones? It’s simply a matter of cost and availability: both work similarly, but the Montmorency tart cherry industry in Michigan provides a convenient supply. There are juices, gels, and powders, all of which seem to work. A typical dose is the equivalent of around 100 fresh cherries a day. And there’s a key misunderstanding that might explain some of the mixed study results, McHugh says: cherry juice is really a “precovery” drink rather than a recovery one. It takes several days of supplementation to build up your defenses against exercise-induced muscle damage, so taking cherry juice after exercise is unlikely to help.
This is the idea that caught my attention, and finally inspired me to take a dive into the cherry juice literature. The key ingredient in tart cherries is their anthocyanins, which are responsible for the red, blue, and purple color of cherries, blueberries, grapes, and various other foods. Anthocyanins have both antioxidant and anti-inflammatory properties, which is why they might help the body handle the heavy oxidative and inflammatory impact of hard exercise.
According to a survey of athletes from 15 countries across 21 sports published last year, 22.6 percent of respondents had used or were using cherry juice supplements. I’d be cautious about taking that number too literally, because when a group of cherry juice researchers recruits subjects “through social media and posters,” you have to wonder if the people they reach might be more likely than average to have heard of cherry juice. The real reason I’m mentioning this study is that one of the 21 sports covered was “weaselling,” which to my disappointment seems to be a distinctively British cross between bouldering and spelunking rather than literally chasing live weasels.
As I said at the top, new studies continue to appear. There was one published just this month from the University of Exeter that shows a nice improvement in post-exercise strength recovery after seven days of loading up on tart cherry concentrate. Other studies published this year look at mental fatigue and mood, blood pressure, and blood sugar control. It’s easy to get excited about the potential benefits, but the overall results remain stubbornly ambiguous. And there are methodological issues, too: for example, some studies require participants to limit their consumption of anthocyanin-rich foods in the days leading up to the experiment. Maybe a normal balanced diet gives you all the anthocyanins you can use, and the benefits only show up if you create an artificial shortage.
Even if the evidence was crystal clear that cherry juice speeds up recovery, there’s a more fundamental question. Anthocyanins fit into a larger body of research on antioxidants and exercise that remains highly controversial, as a recent review explains. As with cherry juice, there’s some suggestive but ambiguous evidence that antioxidants in general may help recovery. But there’s a parallel stream of research suggesting that antioxidant supplements interfere with the gains you’d normally get from both aerobic and endurance training. The reactive oxygen species that produce oxidative damage also happen to be important signaling molecules, telling the body to adapt and get stronger in response to exercise. Neutralize them with antioxidants, and you may feel better tomorrow but be less fit next week or next month.
To be clear, the practical relevance of this research is still being debated. One school of thought argues that you should use antioxidants before major competitions, when recovery is your top priority, but avoid them during heavy training, when the primary goal is fitness gains. This sounds like a nice idea in theory, but I don’t think anyone has demonstrated that it leads to better performance in the real world.
The problem with cherry juice research, generously funded by the cherry industry, is that there’s little incentive to look at the potential for indirect negative effects. I realize that there’s a bit of a catch-22 for supplement companies: if they don’t fund research, they’re criticized for peddling unscientific products; if they do fund research, they’re criticized for biasing the literature. So for the record, I think it’s great that cherry growers are funding good independent studies, even if the results haven’t won me over.
I’m also a big cherry fan. I always keep a bag in the freezer for cereal toppings and smoothies, and I’m especially fond of the tart cherries from my neighbor’s tree. I also love and frequently consume other anthocyanin-rich foods like blueberries and saskatoon berries. I think they’re both tasty and healthy. But to me, there’s a big step from consuming a food to consuming a processed extract or concentrate of that food with the goal of boosting performance. To make that leap, I’d like to see clear and unambiguous evidence that you gain more than you lose—and for sour cherry juice, I’m still waiting.
This article was originally published by Outside.
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