Cardiovascular diseases (CVD) are the leading cause of non-communicable diseases worldwide, with the underlying atherosclerotic process originating in youth. Children and adolescents with CVD risk factors have impaired endothelial function, which is implicated in the process of atherosclerosis. Habitual sugar sweetened beverage (SSB) consumption is associated with the progression of CVD risk factors in youth, and adolescents consume the highest quantities of SSBs. Acute SSB consumption results in vascular dysfunction in adults, though the effects in youth are unknown. It is thought that exposure to CVD risk factors in youth may impair cerebrovascular reactivity (CVR), possibly having implications for future CVD risk. It is also unknown whether the types of sugar in SSBs have different consequences on vascular function. This thesis aimed to investigate the effect of sugar moiety on cerebrovascular function in adolescents, following consumption of a sugary drink and subsequent meal. Data on the reliability of CVR in a paediatric population was needed to first establish if this was a reliable measure of endothelial function. The purpose of this thesis was to: 1) examine the within and between-day reliability of a breath-hold protocol to assess CVR in adolescents. 2) examine the acute effect of sugar moiety (fructose, sucrose, glucose) on CVR and putative blood outcomes, and 3) examine the effects of SSB consumption on postprandial health in adolescents. Chapter 3 examined the reliability of a breath-hold protocol to assess CVR in youth, determined via transcranial Doppler ultrasonography of the middle cerebral artery (MCA). CVR was calculated as the percentage increase in MCAv mean following three breath-hold attempts. This outcome yielded acceptable levels of within and between-day reliability for use in multiple visit experiments to assess CVR in adolescents. Chapter 4 investigated the effect of sugar moiety on cerebrovascular function, measured through breath-hold induced CVR, in adolescents following SSB consumption and a subsequent challenge meal. This study found that the glucose and sucrose drinks resulted in elevated blood glucose levels compared to fructose and water. With consumption of fructose, elevations in uric acid were present, however the sugar moieties all presented similar increases in TAG concentrations following meal consumption. Despite these different metabolic responses, no significant impairments in CVR were present following the drink or challenge meal.
This thesis demonstrated that consumption of SSBs led to increases in glucose and uric acid concentrations, which have previously been shown to be atherogenic. This thesis also provided data on the reliability of CVR as a non-invasive and easy to administer tool for measurement of endothelial function in youth. This is the first study to demonstrate that breath-hold induced CVR can be reliably measured in youth, as a practical, affordable and non-invasive method. These findings provide valuable data that will inform the implementation and analysis of a breath-hold protocol for reliable CVR assessment in youth in future research. Having established that CVR was reliable within and between-day, it was not possible to determine if it was sensitive to change, with no effects seen on CVR following acute SSB consumption. To build on these findings, future research should explore the acute and chronic effects of SSB consumption, with consideration of measuring a range of different vascular outcomes such as changes in peripheral microvascular and macrovascular functions. As this thesis did not include another measure of peripheral endothelial function, it is not certain whether endothelial function was impaired, or if CVR was not sensitive to change in the present study. In order to determine if CVR is sensitive to change, future investigation is needed with established measures of peripheral endothelial function (i.e. flow mediated dilation) alongside measures of CVR.