Monitoring Mucosal Immunity, Upper Respiratory Illness, and the Influence of Vitamin D in Athletes

Abstract

Introduction: Upper respiratory illness (URI) is the most frequently reported illness in athletes, resulting in lost training time and reduced success at competition. Due to the high physical demands on elite swimmers, identification of risk factors associated with URI and individuals at increased risk of illness would be paramount. Individual athletic monitoring of mucosal immunity and identifying risk factors of URI, could enable modification of training and other illness preventative strategies (Gleeson & Pyne, 2016). Vitamin D levels are known to naturally decrease in winter, further increasing risk of seasonal illnesses. However, few studies have examined the effect of vitamin D supplementation on mucosal immunity and the prevention of URI in athletes.

Methods: Study one (Chapter 4) investigated the effect of training load, sleep and EBV status on mucosal immunity and self-reported URI symptoms, for 8-months leading into the 2018 Commonwealth Games. The periodised training load plan for each week was classified by coaches as low, moderate, and high. When this was compared against swimmer’s perceived weekly training intensity, it was significantly correlated. Weekly sIgA was examined to investigate changes in mucosal immunity over different training loads and leading into major competition. Blood samples were taken to determine EBV status and self-reported URI symptoms were quantified using an adapted illness questionnaire. In addition to monitoring self-perceived sleep, quantitative sleep parameters were measured use wrist-worn actigraphy at three different time points during the study period. Chapter 5 presents the development and optimisation of an in-house Enzyme Linked Immunosorbent Assay (ELISA). Assay development and validation protocols were carried out in order to produce an ELISA for determination of sIgA, from the elite swimmer samples in Chapter 4. The final study (Chapter 6) provides a met-analysis and systematic review on the effectiveness of vitamin D supplementation in prevention of URI and the effect on immune markers.

Results: Over the 8-month observation (Chapter 4), 70 upper respiratory symptom (URS) episodes were recorded, leading to 34 days of missed training. Significantly more URS were reported, with increased duration and severity during high training loads. In total, 61% of swimmers had evidence of past infection with EBV. However, EBV seropositivity had no correlation with the number of episodes, severity, or duration of symptoms. When sIgA values were normalised to each individual’s mean, relative sIgA concentration was significantly lower during URS (25%) than when no symptoms were present. No relationship was found for sIgA against training load, and incidence, duration, or severity of URS. Sleep duration was significantly lower during high training loads, plus sleep efficiency was poor throughout the study period. Validation and optimisation of the ELISA was conducted in Chapter 5, which included successful analysis of sensitivity, accuracy, precision, linearity of dilution, matrix effects, range, and intra-variation. Additionally, results from the in-house ELISA were significantly correlated with those from a commercially available assay. The meta-analysis (Chapter 6) found no effect on sIgA, or URS duration and severity following vitamin D supplementation.

Practical Application: The current thesis highlights the importance of individual athlete monitoring for coaches and physiologists to identify athletes at increased illness risk. Identification of risk factors associated with URS, such as increased training load, lowered sIgA and inadequate sleep, may allow for modifications in training or other illness preventative strategies. Overall, elite swimmers showed inadequate sleep; therefore promoting the use of sleep hygiene strategies and napping. There was high prevalence of EBV seropositivity for the elite swimmers; however it was not a predictor of URS. Low participant numbers could be considered for the lack of significant findings with EBV serostatus; there is ongoing debate that individual data and trends may be more useful in elite athletic research, compared to group statistical analysis. Secondly, thesis work presenting ELISA optimisation and validation was successful in offering a good basis for future work. Lastly, findings from the meta-analysis regarding the effect of vitamin D supplementation on URI contrasted with many large cohort studies from the general population. The small number of studies included, low participant numbers, and differences in study design may have influenced these findings. Thus, a clear gap in research is evident and more well-designed control trial studies are needed to establish the relationship between supplementation of vitamin D and URI in athletes.