Blackcurrant news
NewsHub and Radio NZ had stories about New Zealand blackcurrant juice and its claimed ability to make exercise less tiring
Scientists at Plant & Food Research have found that juice from New Zealand blackcurrants consumed prior to exercising could increase motivation to adhere to exercise.
and
Plant and Food science group leader, Dr Roger Hurst says New Zealand blackcurrants are high in the properties, which help your body recover from exercise. He also said polyphenol lifted mood, so that people felt more inclined to exercise better and for longer.
The open-access research paper is here, and the press release is here. It was a placebo-controlled randomised experiment, which is good. Even better, it was pre-registered at the ANZ Clinical Trials Registry, so we can tell what the researchers said they planned to do and match that up to what they say they have done.
Participants drank real or fake blackcurrant juice before a long period of gentle walking on a treadmill. People who drank real blackcurrant juice felt better (by about half a point on a ten-point mood scale) and felt they were exerting themselves less (by about one point on a twenty-point scale). That’s all as the stories claim. The researchers also found a bunch of biochemical things that were consistent with what they expected.
The main critical thing I’d say is that the study registration listed the effect on exercise duration as the first primary endpoint; that is, the main question the study was about. There was no real evidence of any effect on exercise duration, and this negative finding for the primary study question has been rather deemphasised in the press release and media coverage. The research paper does give the exercise results, but doesn’t mention their status as a primary endpoint — I wouldn’t have known if I hadn’t looked up the study pre-registration, and I might well have assumed this was a small preliminary study that wasn’t really expecting to find exercise differences.
Which, of course, is why pre-registration is so helpful.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
Sounds typical , 40 people were tested and the difference is 0.5 on a 10 pt scale. ( half used placebo)
Yet future blackcurrant stories stories will say ‘ Scientist say motivation is increased’ as though its a ‘thing’, the real story of small group and a tiny change is missed.
5 years ago