Polyphenols and Their Effect on Health and Performance in Active Individuals

Abstract

Background: Companies producing polyphenol supplements make ‘health claims’ that their products improve immunity, health and athletic performance based on injudicious scientific research. Polyphenols appear to be effective antioxidants, anti-inflammatory, antiviral and immune-modulating agents, however the degree to which the numerous in vitro studies translate to clinically meaningful human outcomes is undetermined. Currently accepted is the link between exercise load and increased upper respiratory illness (URI), leading to decreased training and impaired athletic performance; less clear is the interaction of dietary polyphenols. Further, there is disagreement to the extent, if any, polyphenol supplementation aids performance. Despite polyphenol supplements being widely available, limited human trials have been conducted with clinically relevant performance and illness outcomes. Consequently, the effect of polyphenol supplementation on health and performance is indeterminate. Objective: The purpose of the thesis was to investigate the effect of dietary polyphenols on health and performance in active individuals to provide efficacy to currently marketed polyphenol ‘health claims’. The predominant supplement under investigation was Olive Leaf Extract (OLE), which contains a variety of polyphenols. Methods: The thesis was a combination of validation, observational and cell-based studies, in conjunction with randomised controlled trials (RCTs), and a meta-analysis. In order to conduct the RCT, a sporting upper respiratory symptom (SUPPRESS) questionnaire was developed and validated, and then implemented to establish URI rates from elite to school age rugby players. Subsequently, high-school student athletes were recruited into a placebo- controlled, double-blind, RCT with OLE supplementation for nine weeks during their playing season to investigate URI differences. Further, a high-throughput cell culture assay screening tool was developed and optimised to identify novel combination of polyphenols that may alter and/or improve metabolic activity and mitochondrial function. Following, active adult individuals were recruited to a crossover double blinded RCT supplementation study for 28 days and completed performance tests, while measuring biomarkers of antioxidant status, URI incidence and training load. Lastly, a meta-analysis was conducted to ascertain the overall effect of polyphenol supplementation on performance. Results: The SUPPRESS questionnaire was developed, validated and used to establish that elite high-school athletes experienced the highest rates of URI. OLE supplementation in this cohort did not alter URI incidence (OR: 1.02 (95% CI 0.21–4.44)) but reduced sick days by 28% (OR: 0.72 (95% CI 0.56–0.93) p-value = 0.02). The high-throughput screening of C2C12 muscle cells identified combinations of polyphenols within OLE may alter cellular metabolism and mitochondrial activity. When active individuals where supplemented with OLE for 28 days however, there was no significant effect on performance (O1.43 ± 5.98%; 95%CI (O4.75O1.88%) p-value = 0.37). Finally, the pooled results demonstrated polyphenol supplementation for at least 7 days increases performance by 1.90% (95% CI 0.40–3.39), and quercetin supplementation alone by 2.82% (95% CI 2.05–3.58). Conclusion and Implications: Polyphenol supplementation appears to have trivial effects on immunity, with more corroboration for improving performance. Although long-term OLE supplementation decreased URI duration, there was no effect on performance. Other polyphenols supplementation regimes however, such as quercetin or anthocyanins, may be more advisable with their reported and now established, dual effect on both URI and performance.