Marathon runners, triathletes, cyclists and other endurance athletes have an increased susceptibility to upper respiratory tract symptoms [URTS], which is associated with longer duration exertion and high-volume workloads (Nieman, 1997). The interesting feature of these symptoms – resembling a common cold that primarily effect the upper airways – is that numerous studies have failed to find any causative link between acute suppression of the immune system and incidence of upper respiratory tract infections (Nieman, 2000; Peters-Futre, 1997; Nieman et al, 1995, Pedersen et al., 1989).
In fact, many of these symptoms are present without any identifiable bacterial or viral infection – hence the characterization of the phenomenon as upper respiratory tract symptoms [URTS] as opposed to upper respiratory tract infections [URTI]. We’re focusing on URTS in this post, which epidemiology indicates occurs acutely in the 1-2 weeks after an exhaustive event (Nieman, 1997), and which also do not follow any seasonal pattern in the way that URTI are observed to (Kuchar et al., 2013). In fact, the non-seasonal pattern and acute nature of the symptoms suggests an underlying cause other than infection, and the strongest evidence implicates inflammation and oxidative stress (Dimitriou et al., 2015).
Endurance exercise increases expression of inflammatory biomarkers in airways, potentially causing bronchoconstriction and allergic reactions (Kuchar et al., 2013). This exercise-induced inflammation is independent of conditions like asthma, albeit may present with similar symptoms, and is a common occurrence in endurance athletes (Bonsignore et al., 2001). Inhaled pollutants and allergens can also aggravate airways, leading to an inflammatory response (Robson-Ansley et al., 2012).
Oxidative stress is also implicated. The term ‘antioxidant’ has become a nebulous, unscientific term due to the prevalence of Insta-babes and their juices. However, as biological creatures who rely on oxygen to sustain life, we go through a process of balancing the generation of potentially damaging byproducts of oxygen metabolism (reactive oxygen species, or ROS) by using endogenous anti-oxidant defence systems to neutralize them.
This balancing act is known as redox balance. The term oxidative stress describes a situation when the capacity of our inbuilt anti-oxidant systems to maintain redox balance is overwhelmed by the generation of ROS (Halliwell, 2007). As a result of the sheer level of oxygen consumption during an endurance event, the production of ROS increases beyond the capacity of endogenous antioxidant defence systems to maintain redox balance (Levers et al., 2016).
Ok, recap – we have a phenomenon of URTS in endurance athletes that is acute (within 14-days post-event), non-seasonal, and distinguishable because of the lack of association with infection or decreased immune function (Nieman, 2000; Peters-Futre, 1997; Nieman et al, 1997; Kuchar et al., 2013; Dimitriou et al., 2015). Rather, the primary causative factors appear to be increased airway inflammation and oxidative stress (Dimitriou et al., 2015). The question is, what can you do to prevent it happening in your next race?
Enter tart Montmorency cherries.
There is a classification of properties of food known as ‘bioactive food components’ [BAFC]: non-nutritive constituents of food that aren’t required for nutrition (like a vitamin or mineral), but that influence health. Montmorency cherries contain high levels of these BAFC, including quercetin and anthocyanins, which have antioxidant and anti-inflammatory properties (Wang et al., 1999; Seeram, 2001). These properties have generated interest in the capacity of Montmorency cherries to reduce oxidative stress and exercise-induced inflammation (Dimitriou et al., 2015).
One mechanism of action relates to their high antioxidant capacity. In a recent randomized double-blind placebo controlled trial (RCT), supplementation with 480mg Montmorency cherry powder for 7-days leading up to a 21km race increased total antioxidant status by 15-31% measured over 48-hours post-race, while the placebo group decreased up to 8% over the same period (Levers et al., 2016). An RCT in marathon runners consuming 8oz cherry juice for 5-days pre-race found a similar effect, in which total antioxidant status remained elevated 24-hours post-race, while the placebo group had returned to pre-race baseline levels (Howatson et al., 2009).
In another recent RCT, lipid hydroperoxide [LOOH], a biomarker of oxidative stress, remained suppressed throughout a simulated cycling road race, with a series of 66 sprints of 5, 10 or 15 seconds duration, after 4-days of consuming 60ml cherry juice (Bell et al., 2014).The exact mechanisms of action remain unclear, and several mechanisms have been proposed, including acting directly as free radical scavengers and upregulating antioxidant defences (Traustadottir et al., 2009).
Anthocyanins may not be responsible for an immediate effect given their poor absorption and half-life of 90-120 minutes, but the above studies all used pre-race loading phases and the antioxidant effect of anthocyanins may reflect a time-interaction and dose-response (Bell et al., 2013). Quercetin may have a more direct effect, because this BAFC does act to scavenge reactive oxygen species (Boots, Haenen & Bast, 2008). Quercetin is absorbed with better efficiency (50% from food sources), and with a half-life of 11 to 16 hours, can accumulate and increase plasma antioxidant concentrations (Bell et al., 2013).
At this point, the most likely mechanism is the upregulation of endogenous antioxidant capacity. Both anthocyanins an quercetin have been shown to reduce markers of oxidative stress, including LOOH, an effect which may be mediated by activating glutathione, a potent endogenous antioxidant (Zhu et al., 2012; Girotti, 1998; McCune et al., 2010). Like most BAFC, it is likely the quercetin and anthocyanins act synergistically (Bell et al., 2013; McCune et al., 2010).
An RCT in London marathon runners found that C-reactive protein, a biomarker of inflammation, was significantly lower than placebo up to 48-hours post-race following consumption of 472ml cherry juice (divided into two 236ml doses, one in the morning and another at lunch) (Dimitriou et al., 2015). A similar study found the same effect: increases in CRP were 34% lower than placebo group in marathon runners measured at 24 and 48-hours post-race (Howatson et al., 2009).
A feature of these studies is that subjects consumed cherry juice for 5-7 days pre-race, the day of the race, and for the 48-hours post-race (Dimitriou et al., 2015; Howatson et al., 2009; Levers et al., 2016). Consistent high intake of anthocyanins has been associated with lower CRP levels, potentially to be through suppression of pro-inflammatory mediators (Jennings et al., 2013).
The other factor in URTS inflammation is inhaled pollutants over the course of an event, and quercetin may attenuate pollutant-induced airway inflammation (Dimitriou et al., 2015). It has been proposed that the primary mechanism by which Montmorency cherries mediate exercise-induced inflammation is through inhibition of inflammatory cytokine expression, particularly in the post-exercise recovery period (Levers et al., 2016; Lyall et al., 2009). At 1-hour following a half-marathon, increases in the stress hormone cortisol were 44% in the placebo group compared with 15% in the Montmorency cherry group (Lyall et al., 2009).
The pro-inflammatory cytokine Il-6 is consistently reduced by 30-50% with Montmorency cherry ingestion (Nieman, 2000; Levers et al., 2016; Bell et al., 2014). The overall mechanism of anti-inflammatory action may be through inhibition of COX2 enzymes (Seeram, 2001), and inhibition of COX2 has been shown to reduce both IL-6 and CRP (Monakier et al., 2004).
The evidence that Montmorency cherry consumption prevents susceptibility to URTS after endurance events, in particular evidence from RCT’s, is strong. While the mechanisms of action remain unclear, the likelihood is a synergistic anti-inflammatory and antioxidant effect from multiple bioactive food components.
So, what’s your action step for your next event?
Dose: 236ml (8fl oz) Montmorency cherry juice OR 30ml of concentrate (dilute to drink);
Timing: Taken once in the morning and again with lunch;
Duration: 5 days leading up to the race, the day of the race, and 48-hours after the event.
This is a very simple, effective and actionable strategy. Put it into place for your next event.
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