Friday, 1 February 2013

Cherry-picking the evidence?

A good friend of mine is really into running, and has many half-marathons, kilomathons, and marathons under his belt (at least one of which was in a very hungover state). He is taking a sour cherry supplement, which has led to some heated debate about whether or not it works.

He eagerly googled, to bring up some small studies of the effects of sour cherry juice on pain after a marathon. More animated discussion took place. He seemed to think that the very existence of some studies meant that the stuff would definitely work:  So I thought this would be the perfect place to assess what evidence there is for sour cherry.

It would seem that there are several different types of cherry, sweet and sour. It is the sour, tart varieties which appear to be of interest in exercise products such as this. And these things are pretty expensive.

My first point: the evidence appears to be looking at juice, not tablets. There is nothing to say that any benefits you might get from a juice will also be present in a tablet- think of garlic, for example, where allicin, the active ingredient, is mainly lost during the processing required to make a garlic supplement.

My search strategy begins with my old friend Embase. eagerly, I find sour cherry in the database and search it, only to get 9 results. When I limit it to humans, I get 1 result, and that is assessing its effects on sleep quality, so is nothing to do with exercising.

And so, I move onto Medline, in which I find a grand total of 2 studies looking at the effects of sour cherry juice in recovery following exercise.

The first study has 20 recreational marathon runners in it, so its tiny, and far too small to be able to draw any reliable conclusions from. Whilst it seems to show some positive results, with significant reductions in isometric stress, inflammation, and oxidative stress, there is no indication of how relevant this is clinically.1. Would I actually feel better after a marathon as a result of this? Is this increase in recovery of muscle function actually going to make a difference?

The second study has a grand total of 14 male students in it. It's randomised and placebo controlled, but again, to small to be of any interest. This study found that strength loss and pain were reduced in the cherry group, but relaxed elbow angle and muscle tenderness were no different. 2

There are a couple of other little trials dotted here and there are well. But they're all too small to suggest that there is any definite effect. Moreover, there is no information on the safety of such products. Any trials only apply to cherry juice, and can't as yet be extrapolated to cherry supplements such as tablets or capsules.

Whilst the preliminary evidence looks juicy, it's certainly not enticing enough to tempt me to pop my marathon cherry.

I'll stick to my favourite types of cherries, if you don't mind, namely those that are steeped in sugar and  encased in pastry.

Search strategy:
Embase:*sour cherry [Limit to: humans]
Medline: (sour AND cherry).af OR (tart AND cherry).af [limit to: humans]

1. Howatson G et al. Influence of tart cherry juice on indices of recovery following marathon running. Scandinavian Journal of Medicine & Science in Sports, 12 2010, vol./is. 20/6(843-52), 0905-7188;1600-0838
2. Connolly D et al. Efficacy of a tart cherry juice blend in preventing the symptoms of muscle damage. Br J Sports Med 2006; 40: 679-683