Nutritional interventions for thyroid function in adolescent academy footballers

Boldon, Ruth (2021) Nutritional interventions for thyroid function in adolescent academy footballers. Doctoral thesis, Northumbria University.

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Abstract

Thyroid function is vital for health, with direct impacts on metabolic rate and energy production. Research has established that exposure to various stress factors can inhibit thyroid function and supresses circulating thyroid hormones (THs). These stress factors include maturation, fasting, poor nutritional intake and increased exercise energy expenditure (EEE). It is hypothesised that these adaptations are due to altered peripheral conversion of thyroxine (T4) away from the active hormone triiodothyronine (T3) and toward the inhibitor reverse-triiodothyronine (rT3). Consequently, adolescent athletes are a unique population in the sense that they can be presented with a plethora of these stress factors concurrently, yet the combined impact of this on thyroid function has not been confirmed. The aim of this thesis was to elucidate the impact of various stress factors on thyroid function in adolescent male footballers and identify periods in maturation and the sporting season when thyroid function could be at risk, with the final intention of developing a nutritional intervention in an attempt to mitigate any suppression of THs. It was hypothesised that thyroid function would be supressed under high training loads, under low energy availability (EA), during maturation and when carbohydrate intakes were low. As such it was hypothesised that providing a nutritional load to rectify the energy and carbohydrate deficits would help to preserve thyroid hormone concentrations during periods of high stress. In Study One and Two, Liquid Chromatography–Mass Spectrometry (LC-MS) analysis was confirmed as a valid, reliable and logistical method for assessing THs in adolescents and it was suggested that body temperature and blood pressure could potentially be surrogate markers for thyroid function. Study Three showed that those in peak height velocity, with low EA and with low carbohydrate intakes were more likely to have supressed TH concentrations, particularly after a competitive football match. Study Four suggested that a post-exercise carbohydrate drink can mitigate some of the acute suppression of T3 (<60 mins), however for longer term benefits, a more systematic approach to increase energy intake might be required. This work extends understanding of supressed TH concentrations during periods of stress and provides valuable insight into when thyroid function might be at risk within adolescent male footballers. These findings highlight the importance of adequate energy and carbohydrate intakes in adolescent athletes, particularly when undergoing bouts of heavy training and during maturation.

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