Blood biomarker monitoring in professional soccer: Longitudinal analysis of inflammation in English Premier League players

The high intensity demands of elite soccer predispose players to recurrent episodes of acute inflammation, and during periods of frequent match play recovery time may not be adequate for the resolution of the inflammatory response. Given the link between chronic inflammation and a host of sport specific medical problems, the monitoring of blood biomarkers of inflammation in athletes may be a medical and performance objective for protecting player health, recovery and adaptation. However, longitudinal studies examining biomarkers of inflammation in the English Premier League are absent from the literature. Therefore, the primary aim of this thesis was to examine inflammation in English Premier League players. The secondary aim was to investigate strategies which may reduce inflammation during the competitive season when the ability to recover in sufficient time may be compromised. The successful application of blood biomarker monitoring programs in elite sport is not only hindered by the need for more frequent testing but also by an understanding of meaningful changes in biomarker data. Therefore, the aim of the first study (Chapter 4) was to; Part 1: investigate the level of agreement between the standard laboratory method and a point of care test for C-reactive protein obtained from thirty five professional soccer players with physiological concentrations below 5 mg/L, over the course of 3 English Premier League seasons; Part 2 : calculate the analytical variation for the point of care measurement of C-reactive protein in well trained participants (duplicate samples) (n=10); Part 3: To calculate the biological variation and critical difference value for the point of care measurement of C-reactive protein in well trained participants who had capillary samples taken every morning for 5 consecutive days (n=8). The average difference between the two methods was 0.27 mg/L with the standard deviation of 0.115 mg/L and limits of agreement of -1.7 mg/L to 2.24 mg/L. Repeatability of the point of care assay was 5.26%, biological variation was 5.03% and the critical difference value was 20.1%. We report that the use of a point of care test for C-reactive protein in well-trained individuals is practical, but not interchangeable with the standard laboratory method, and the critical difference value reported here may be used to enhance interpretation of meaningful changes in C-reactive protein in well trained individuals. The aim of the second study (Chapter 5) was to examine blood biomarkers of inflammation and oxidative stress simultaneously with workload and wellness data in response to weekly match play in 22 players across the first half of an English Premier League season. We report that a competitive English Premier League game induces time-dependent changes in circulating markers of inflammation and oxidative stress, pre-match inflammation status predicts post-match inflammatory response, and pro-oxidant status significantly increase across the first half of an English Premier League season. The point of care measurement of inflammation was found to be highly sensitive in detecting subjective feelings of fatigue, muscle soreness and the presence of illness symptoms. No significant relationships were observed between match workload and biomarker responses. Our data suggests that the pre-game may be an important window for practitioners to reduce inflammation, since it is unlikely they can influence player match selection and that the POC measurement of C-reactive protein in conjunction with wellness data may offer an objective tool for identifying fatigue and illness risk in professional soccer. The aim of the third study (Chapter 6) was to investigate the effect of curcumin supplementation on biomarkers of inflammation and oxidative stress in response to weekly match play during an EPL season. We used an interrupted time-series design to analyse the effect of curcumin supplementation on biomarkers of oxidative stress and inflammation in healthy players. Following a seven-game control period, participants completed a four-game supplementation block, followed by a second control period of two games and another supplementation block of five games. We report that curcumin ingestion had no significant effect on inflammation, and had borderline significant effects on pro-oxidant responses. However, the magnitude of this change does not appear to be physiologically relevant, suggesting that at a group level curcumin ingestion using the dose and protocol prescribed may not be effective for attenuating inflammation and pro-oxidant status within the real world, applied, field setting of elite soccer. We therefore question the efficacy of curcumin supplementation in elite soccer players following their habitual diets. The kinetics and resolution of inflammation may be influenced by the nutritional status of the athlete, and measuring the composition of the erythrocyte membrane fatty acids and examining its association with inflammation could clarify the role of fatty acids in the development of low-grade inflammation in soccer players. Therefore, the fourth aim of the thesis (Chapter 7) was to examine, for the first time, concurrent seasonal alterations in erythrocyte membrane fatty acid composition and inflammatory markers and determine whether inflammatory status is associated with certain fatty acid parameters in professional soccer players (n=35) over the course of 3 seasons. We report significantly higher mean inflammation values, in the winter period compared to the pre-season. Moreover, time-dependent changes were also observed for omega-6 and omega-3 fatty acid variables, with the former decreasing and the latter increasing from the pre-season. We report a significant negative association between C-reactive protein and the omega-3 Index, and a significant positive association between C-reactive protein and the omega-6:omega-3 ratio, suggesting that fatty acid status is a significant driver of low-grade inflammation in professional soccer players. Together, we present convincing evidence that the erythrocyte membrane fatty acid composition influences the changes in inflammation observed across time in the elite soccer player. Large between subject variability in biomarkers mean that individualised approaches to biomarker monitoring may be of higher potential value in protecting player health or detecting an under-recovered state. Therefore, the fifth and final aim of the thesis (Chapter 8) was to explore the application of individualized adaptive reference ranges in professional soccer players competing in the English Premier League using point of care tests for C-reactive protein and hydroperoxides biomarkers. Secondly, we aimed to investigate whether the observed changes in blood as a result of curcumin supplementation are greater than the previously reported critical difference value for the aforementioned biomarkers and therefore of physiological significance for each player. Our study confirms that athletes deemed “healthy” or “non-healthy” present markedly different within- and between-subject variations in biomarkers values, which has a significant impact on their respective individualized ranges. Physiologically relevant changes in C-Reactive Protein levels were observed for only 3 athletes in the study group in response to the intervention, with no athletes displaying substantial decreases in hydroperoxides. The individualized approach presented here may be used to identify athletes that require recovery or clinical review, however, the results of this study highlight that human interpretation of is still required in order to intuitively observe trends in biomarker data. Future work investigating this individualised approach to longitudinal biomarker monitoring are required in elite soccer. The results of this thesis have shown that the point of care measurement of C-reactive protein provides a minimally invasive assessment that is sensitive to the changes in subjective feelings of wellness and illness and may assist in protecting player health and availability for team selection. We also show that the pre-match (i.e. game day -1) and the winter period of the English Premier League may be important windows to reduce inflammation. Furthermore, our findings provide rationale for augmenting the erythrocyte membrane fatty acid composition as a potential “pro-resolving” strategy during periods of limited recovery. We present an individualized approach to biomarker monitoring which may help guide the practitioner’s interpretation of individual biomarker data, however, future studies are warranted in order to transform this promising strategy into an efficient monitoring tool in a real world setting