*4.3. Tart Cherry Juice*

Tart cherries contain approximately 13 ng of melatonin per kg of cherry [52], which upon consumption can increase exogenous melatonin, which is critical for the sleep–wake cycle in humans [53]. The high antioxidant content of tart cherries purportedly reduces oxidative stress, in turn enhancing sleep in isolation and in conjunction with melatonin. The reported anti-inflammatory properties may influence the pro-inflammatory cytokines involved in sleep regulation and also the recovery process after exercise [10,52]. The majority of studies investigating tart cherry juice usage in an athletic population have examined its effect on aspects of recovery including muscle soreness [54–56]. While promoting recovery is beneficial to athletes, tart cherry juice has enhanced sleep indices as assessed by PSG and wrist actigraphy monitoring in healthy individuals without the presence of sleep problems [31], and individuals with sleep problems such as insomnia [27]. Other studies have demonstrated that tart cherry juice can increase TST and SE, regardless of the differences in participants (good sleepers compared to individuals with insomnia) [27,57]. Consumption of a liquid blend consisting of Montmorency tart cherries and apple juice improved sleep in older adults with chronic insomnia by decreasing WASO, and reducing their insomnia questionnaire score compared to baseline [27].

The efficacy of tart cherry juice as an intervention to improve indices of recovery in marathon runners has been investigated [58]. Consumption of a tart cherry juice blend taken in the morning and afternoon (~240 mL) elicited a more rapid return of strength postrace and smaller elevations in inflammation markers (i.e., c-reactive protein, interleukin-6, and uric acid) compared to placebo [58]. It appears that tart cherry juice may be effective at accelerating the recovery process and restoring strength, even after high-intensity endurance exercise. However, there are claims that the use of antioxidants in an athletic population is questionable given potential blunting of the training adaptation response, and reduced training efficiency [59]. One authoritative consensus group indicated that tart cherry juice interventions in athletes is not recommend nor endorsed [60]. Further research is needed to assess the use of tart cherry juice in an athletic population, including its effects on sleep and physiological recovery.
