The physical exercise in which athletes take part in competitive sport may result in a disturbance of homeostasis of the body, which in turn leads to much worse sports performance, as well as a deterioration of health. Analysis of the available literature indicates that the compounds contained in chokeberry have strong antioxidant activity. In this respect, a key role is attributed to anthocyanins, which prevent the excessive formation of free radicals, namely superoxide, hydroxyl, nitrite and chlorine radicals [16, 17]. The anti-radical activity of these compounds is increased by the number of hydroxyl groups on the B ring and the arylation of sugar residues with phenolic acids. As demonstrated in the studies of van Acker et al., anthocyanins have 100 times higher activity in nitric oxide radical (•NO) removal than the endogenous antioxidant glutathione [18]. Due to the presence of hydroxyl groups in the C ring, these compounds are able to chelate transition metal ions (e.g. iron and copper) [19]. Another important feature of anthocyanins from the point of view of health is their ability to inhibit lipid peroxidation [20], which can be of great importance in reducing haemolysis induced by intense physical exertion.
Research shows that the antioxidant capacity of chokeberry measured by total antioxidant capacity (TAC) as well as the strength of reduction of Fe3+ to Fe2+ is very high and depends on weather conditions; the presence of active compounds is influenced by both the average air temperature and hours of sunshine from May to September [21].
The antioxidant potential of the chokeberry juice given to football players was measured using two methods, DPPH and ABTS, as 8.83 mg/ml and 7.62 mg/ml, respectively (relative to the activity of the Trolox reference compound), which indicates that it was relatively low. This can probably be explained by the lack of statistically significant differences demonstrated not only in the level of TAC, but also in other biochemical, morphological and performance parameters in football players (Tables 3a, 3b, 4 and 5).
Petrovic et al. used chokeberry juice supplementation in handball players and showed that 100 ml/day supplementation of chokeberry contributed to small changes in the lipid profile and reduced TBARS levels; however, these changes were observed only in men [22]. In our research, the chokeberry juice dose was twice as high, which had no effect on the reduction of free radical damage measured with both TBARS and 8-OHdG levels (Table 3b). García-Flores et al. combined chokeberry extract with citrus juice (200 ml of drink was 95% fresh citrus juice and 5% chokeberry extract); this combination of ingredients significantly reduced post-exercise changes in the level of DNA damage markers measured in both the plasma and urine of triathlon riders [23].
Analysis of the available literature indicates that the advantage of compounds derived from chokeberry is their comprehensive effect on both the immune system and reduction of oxidative stress, including the ability to chelate iron ions, which seems to be a key element not only for iron management. For this reason, we expected it to reduce markers of oxidative stress. However, the lower (statistically insignificant) average values of the tested markers of oxidative stress, obtained in the second test period (after supplementation), concerned both the supplemented and control groups, which may be a result of the players’ adaptation to the applied exercise loads. Zügel et al. analysed the cumulative effect of training stress in highly qualified athletes practising rowing on the level of hepcidin and its impact on parameters related to iron management. They showed that the levels of hepcidin and ferritin as acute-phase proteins were a sensitive indicator of changes in training loads (increase in volume and intensity of exercise). In their own research, football players were subjected to the same training loads throughout the entire study period (Table 2), which probably explains the lack of statistically significant differences in the levels of hepcidin and ferritin (Table 3a) [24]. In other studies conducted by the team of Villaño et al., the effect of physical exercise and supplementation with juice high in polyphenols (the juice also contained chokeberry extract) on the level of hepcidin was analysed in a group of triathletes of both sexes. The study did not show a significant impact of the supplement on this parameter, while its reduction was associated with adaptation of the players’ bodies to the applied exercise loads [25].
In our study of footballers, interesting trends related to iron levels were observed in the second study period; namely, the level of this parameter after 3 h of rest in the supplemented group decreased, while in the control group it increased (Tables 3a and 4). Similar changes in iron levels were observed by Punduk et al. in volunteers who received intensive platelet-rich plasma therapy during intense exercise. This therapy aimed to improve muscle regeneration, which was damaged by the use of high-intensity exercises (exercise-induced muscle damage, EIMD) [26]. It can be assumed that the ability to chelate iron ions, through the active compounds contained in chokeberry, can also counteract damage to muscle fibres. Confirmation of this thesis can be observed from the changes in myoglobin level in subjects, although they were not statistically significant (Table 3a). Myoglobin is a marker of muscle fibre damage; in the group supplemented with chokeberry it showed a downward trend, while in the control group the level of this parameter increased.
In the inflammatory process, the role of anthocyanins can result from both the ability to sequestrate iron [27] and from their regulatory action on various components of the immune system involved in the development of inflammation [28]. Research conducted by Ohgami et al. on animal models has shown that chokeberry extract has a strong anti-inflammatory effect on endotoxin-induced uveitis in rats. The authors observed that the number of inflammatory cells, the protein concentration, and the levels of NO, pyrogenic prostaglandin E2 (PGE2) and TNF α in the aqueous humour in the groups treated with aronia crude extract were significantly reduced, and effect strength depends on the dose used [29]. For this reason, the standardization of chokeberry products for the presence of anthocyanin compounds, which play a key role in health protection, may be of great importance.
Summing up the research results presented above, it can be stated that the use of chokeberry products in the diet did not cause significant changes in the parameters analysed. The reason could be both good adaptation of the examined players to their physical exercise, and the use of juice with low antioxidant capacity. Therefore, it seems reasonable to consider the use of chokeberry extracts standardized for the presence of anthocyanins. Another issue that should be explored is to understand the mechanisms of how and what compounds contained in chokeberry may be responsible for improving the parameters studied.