Factors affecting hepcidin in athletes

The aim of thesis was to investigate some of the factors affecting hepcidin, which are influenced by a variety of training, physiological and nutritional aspects common in the everyday lives of athletic populations. Chapter 4 (Study 1) investigated if a resting ischaemic preconditioning (IPC) protocol increased hypoxia and inflammation. These factors have contrasting influences on hepcidin and therefore the net outcome on hepcidin is unknown. This study demonstrated that, although there was a significant increase in hypoxia-inducible factor-1α for the IPC trial (p = 0.031, ES = 0.60), a resting IPC protocol does not increase hepcidin above and beyond the response to diurnal variation (IPC vs Control Trial p = 0.418). Chapter 5 (Study 2) aimed to investigate if vitamin D status was related to hepcidin concentrations before and following exercise. This study demonstrated a significant association between vitamin D and pre-exercise hepcidin concentrations (r = 0.430, r2 = 0.185, p = 0.036) this was not evident following exercise (3h post-exercise, rho = 0.328, p = 0.117). Chapter 6 (Study 3) aimed to further understand how the female menstrual cycle (MC) interacts with hepcidin and iron regulation within females of varying training and exercise levels, from low volume recreational exercisers to elite athletes. Both oral contraceptive (OC) users and non-oral contraceptive (NOC) users were investigated. This study demonstrated that hepcidin levels differ over a menstrual cycle (p < 0.005) and with elite status exerting the largest influence on hepcidin (~14 ng/mL increase for every ng/mL in non-elite females), ferritin (~-23 μg/L decrease in ferritin for every μg/L in non-elite females) and iron (~-4 μmol/L decrease in iron for every μg/L in non-elite females) in OC users, and iron (~-2 μmol/L decrease in iron for every μg/L in non-elite females) within NOC users. However, oestrogen and progesterone levels were not significantly associated with hepcidin or iron status. Chapter 7 (Study 4) built on the previous 2 chapters, investigating whether hepcidin responses post-exercise differ between MC phases in NOC using females and whether vitamin D status influences the response. In agreement with the previous chapter, hepcidin levels differed significantly between the MC phases (LF significantly higher than ML, p ≤ 0.001, ES = 0.99) yet the levels of the specific sex hormones were not significantly associated with those of hepcidin (17β-oestradiol, r ≥ -0.393, p ≥ 0.296; progesterone, r ≥ 0.503, p ≥ 0.168). In addition, Vitamin D status was not significantly associated with hepcidin (r ≤ 0.56, r2 ≤ 0.32, p ≥ 0.114). This thesis provided evidence to further our understanding of the factors which influence hepcidin within athletes, although additional investigations into specific mechanisms is required. This information will help aid decision making on the management and monitoring of iron status in athletic populations, enabling greater optimisation of their health, training, and competitive performance.