By Glyn Howatsen and Asker Jeukendrup
Tart cherry juice has become increasingly popular as a recovery aid and the scientific evidence seems to be growing. I caught up with Professor Glyn Howatsen who wrote an excellent blog on cherry juice for mysportscience, based on the studies that his team and others performed. The results seem very promising but I still had a few questions and could not find the answers in the literature. So I asked Glyn for his expert opinion.
AJ: Hi Glyn, thanks for the great blog and for the willingness to answer a few more questions. I usually call it "the stuff you don't read in the papers". When I read the literature my conclusion is that the results of cherry juice studies are not uniform. I also get the impression that some results could be the result of an inability to completely blind subjects. What is your view on this?
GH: Results are not uniform form many variables, but function is shown consistently to change, which from an athletic perspective is absolutely critical. If metric like maximal voluntary contraction (MVC) return faster, then by inference your ability to produce power is also returning faster. If function is in good shape, then any subsequent training and competition will be completed close to optimal (or at least baseline). There is a real issue with blinding for many studies, so conceptually if the participants know about cherries, then there could be a placebo or participant belief effect.
However, most studies show improvement in other indices that are difficult to explain by a lack of blinding - mostly in inflammation. Perhaps some psychosomatic effect is possible, but I suspect that a little belief in an intervention will unlikely translate to modulation of IL-6 or CRP, for example. Although the taste of cherries are distinctive, most (but not all) use a cherry flavoured or fruit flavoured cordial that is matched for macro-nutrient value and the participants are told the trial is about the efficacy of a fruit juice, not cherries. Lastly, although some indices do not show an effect, there are no negative responses. Thus cherries do not seem to have detrimental effects.
AJ: How strong do you think the evidence is? From a practical point of view how promising is it? Is it worth the investment and is it indeed low risk?
GH: There is a good range of studies in isolated muscles (using high intensity eccentric contractions). This is all very interesting and provides some proof of concept, but they lack task specificity to what athletes might encounter. In a series of studies we (and others) have tried to use this intervention in Marathon running, simulated road race cycling conditions and simulated repeated sprint sports (football, for example). The bottom line is that the evidence is very promising and at the moment seems unequivocal. I think from my perspective the athlete and practitioner needs to weight up the risk/benefit balance. From the current evidence there is nothing to lose and everything to gain; at the very least you ensure that the athlete is getting a polyphenol-rich fruit portion.
AJ: You mention that it is only this type of cherries… What is so special? What is the most likely active compound?
There are plenty of cherries in the supermarkets (Morello, Bing and so on). These are the same genus (Prunus; the same as apricots, peaches, plums) and in the case of Morello, the same species. However, despite being the same species the cultivars are different and the phytonutrients found are also different. It is very much like wine, where soil, environment, geography and seasonal variations can influence the goodies in the cherries. Montmorency cherries, which are largely from North America, are rich in polyphenols and anthocyanins and it is these compounds, and their downstream metabolites (phenolic acids), that are thought to be the bio-active plant compounds.
AJ: Now lets turn this into practical recommendations. Studies are all different… different number of days, slight different doses etc. What would you say is the perfect dose…. If there is such a thing? How many days would you use it? Before or after the event, or daily during a period with a congested competition schedule?
Is there a better time of day to take it? Any other recommendations?
GH: If you know what the schedule is, then it makes sense to start taking the juice in the days leading up to and after the event/session. Routinely, where recovery and NOT adaptation is the primary concern (for example rugby and football) because playing schedules are congested, players will have it on the table at meal times. I do not know if co-ingestion with other foods affects absorption, but in most cases, participants are instructed to consume the beverage in the morning and the evening around meal times. I think the crux of the whole thing is to provide the substrate when there is trouble (strenuous exercise), so it can act on the potential negative effects (probably oxidative stress and inflammation). Given the pharmacokinetics (the absorption, digestion, action and excretion) intake in the morning and afternoon/evening seem pragmatic. I would personally be tempted to take the PM dose about an hour before bed to potentially facilitate a better nights sleep.
If you consume a concentrate (often diluted with 100-200 milliliters (3-7 fl oz) of fresh water) then you need 30 milliliters (1 fl oz ) of the concentrate taken twice per day. However, we have done some bioavailability studies and showed that the compounds we think are having an effect tend to peak and subside within a few hours. So, if there is a benefit of a ‘loading’ phase for 3-5 days then these compounds are perhaps being stores in tissue somewhere - I have my doubts! However, ALL studies used a loading phase and ALL show some benefit - the easy way to conclusively address this is to only supplement after the event and see if the responses are similar.
AJ: Now that would be a great study and important from a practical point of view. Please let us know when you have done this study. Or perhaps one of our readers now has a great idea for a research project. Thanks very much Glyn for your insights and please keep us informed about any new developments in this area!