Polyphenols and their effects on sports performance

Abstract

In recent years, many different ideas have been put forward to improve the antioxidant potential and accordingly improve physical performance by improving nutrition and other related factors. Whether the athletes use or not use antioxidant supplements is an important issue that is discussed a lot (1). In this review, information about well-known and recently used antioxidants, primarily polyphenols, will be given and only human studies will be included. In addition, the effects of the polyphenols in the studies on exercise performance and exercise-induced oxidative stress will be explained.

This review article was prepared to compile the results of the studies investigating the effects of polyphenols on sportive performance by scanning the national and international literature between the years of 2022 and 2023. While searching, "Ebsco TR Index", "DergiPark Academic", "National Thesis Center" for national databases, “Polifenol”, “Polifenol Takviyeleri”, “Sportif Performans”, “Polifenol Takviyeleri and Sportif Performans” in databases, international databases for “Google Scholar”, “Pubmed”, “ScienceDirect”, “Scopus”, “Web of Science”, “Proquest”, “Ebsco Host” databases “Polyphenols”, “Polyphenols Supplements”, “Sportive Performance” and “Polyphenols Supplements and Sportive Performance” keywords were used.

Free radicals and reactive oxygen species (ROS) are the main oxidizing agents in cellular systems and play a role in aging and the onset of many types of diseases. Free radicals are produced physiologically in the mitochondria for aerobic oxygen production, in fatty acid metabolism, drug metabolism, and in the body when the immune system is activated (2-4). Although these free radicals have positive effects on immune reactions and cellular signaling; it is also known that lipids, proteins and nucleic acids have negative effects such as oxidative damage (2-5). ROS production induced by exercise and physical activity is an important signaling pathway to promote biological adaptations to training (2,3). However ROS production can have detrimental effects on lipid and protein peroxidation such as cells and tissues. In order to prevent this situation, some health professionals have given importance to the consumption of more nutritional supplements and supplements containing antioxidants in order to reduce the production of ROS, which can cause excessive oxidative stress during and after exercise (4,5). Antioxidants are defined as to be donate an electron to free radicals and neutralize, reduce or eliminate their ability to damage cells, major biomolecules such as nucleic acids, proteins and lipids (2,3). Antioxidants are divided into two groups as enzymatic oxidants (Superoxide dismutase, glutathione peroxidase, catalase enzyme) and non-enzymatic antioxidants (glutathione, vitamin E, vitamin C and bilirubin). Endogenous antioxidants have the function of delaying or preventing the oxidation of extracellular and intracellular biomolecules. Antioxidants, such as vitamins and minerals taken with food can also regulate the oxidative state of the body (2). There are still ongoing conflicts in studies investigating the effect of antioxidant supplementation on exercise-induced oxidative stress. Typical treatment usually includes various doses of vitamins A, C and E, administered either alone or in combination, chronically or acutely (6,7). Of these, vitamins C and E are used more frequently in clinical and experimental studies, mostly because they are safe and easy to find (6).

Recently, one of the topics that have been widely covered in the literatüre is that there has been a potential relationship between oxidative stress and bioactive compounds found in plant foods. In particular, the attention of researchers has turned to the effects of polyphenols, a bioactive nutraceutical compound that has attracted considerable interest. One of the first studies that attracted the attention of scientists was Zutphen's epidemiological study (Keli et al., 1996). In this study, a negative correlation was found between the intake of foods rich in polyphenols and the incidence of chronic diseases (diabetes mellitus (DM), cardiovascular diseases (CVD) and cancer, etc.) especially associated with a significant oxidative stress (8). For this reason, new nutritional strategies were being developed against oxidative stress caused by exercise, and in this sense, especially PP supplements were given importance. It is thought that polyphenol supplements were effective in improving performance and preventing oxidative stress in athletes (1)

Polyphenols (PPs) are natural organic compounds found in abundance in different plants, fruits, vegetables, nuts, seeds, flowers, tea and beverages (9). Polyphenols are more important due to their diversity, bioactivity, easy accessibility and lower toxicity effects, and their specificity in terms of antioxidant response (10). Today, there are many studies on PPs and physical exercise (11-13). Most of these studies include topics that cover both the important effects of polyphenolic compounds in exercise-induced muscle damage and their biological/physiological roles in improving physical performance. In order to measure the effects of polyphenols on sportive performance, various supplementation strategies were applied at different times and dosages, and studies were conducted in a wide variety of exercise conditions. In the literature, there are studies on PP supplements, especially quercetin, catechins/green tea extract (GTE), resveratrol and polyphenol mixtures in athletes.

Studies on quercetin supplementation in athletes have focused on the potential effects of exercise-induced inflammation, oxidative stress, immune dysfunction, and exercise performance (14). It is thought that catechin supplements will positively affect sports performance due to their high antioxidant content and activation of catechins with anti-inflammatory potential (12,13,15). There are few studies in the literature investigating the effect of RES on exercise performance, and some results show that it may be effective in increasing endurance capacity. Nowadays, studies investigating the relationship between RES and exercise are increasing, because it is thought that RES supplementation may have positive effects on the regeneration of liver cells, protect the liver glycogen stores that decrease during physical activity, and have a regulatory effect on glucose metabolism (15). Moreover, it has been observed in recent years that research has focused not only on the effect of PP supplements alone, but also on the biological effects of PP-containing mixtures. In this sense, many studies have been conducted with athletes using blueberry, blackcurrant, cherry juice, pomegranate, dark chocolate, turmeric/curcumin, honey, carob pulp powder (16-23).

In conclusion; although PP supplements are still a controversial issue in athletes today, application of different exercise protocols to athletes, obtaining different results about PP supplements and using different laboratory parameters to evaluate these effects make it difficult to understand the effects of PP supplements on athletes. Therefore, in order to analyze the data correctly and compare it with other studies on this subject, the type of exercise (aerobic or anaerobic), the oxidative stress biomarkers used, the athlete and training characteristics should be explained in detail in the method part of the study (1). At the same time, it is thought that nutritional protocols should be examined in more detail in studies and the amount of PP intake from nutrition in athletes should be calculated.