The effects of sitting on cerebrovascular and cognitive function

Abstract

Sedentary behaviour (SB) has emerged as a risk factor for cardiovascular morbidity and mortality, independent of physical activity (PA) levels. Despite associations between SB and cerebrovascular disease, little research has assessed the influence of SB on cerebrovascular function, comprising cerebral blood flow (CBF), cerebral autoregulation (CA) and cerebrovascular carbon dioxide reactivity (CVR). This is of upmost importance since the maintenance of cerebrovascular function appears critical for cognition, mood and the prevention of cerebrovascular diseases. Consequently, the overarching aims of this thesis were to explore the effects of sitting on cerebrovascular function, cognition and mood and to explore the effect of breaking up sitting on these parameters. Study one assessed whether objectively measured workplace sitting and PA were associated with cognition and mood. Results showed workplace sitting was negatively associated with calm mood state, but not cognition. Standing and stepping whilst at work were positively associated with aspects of cognition (working memory and attention) and mood (positive affect and calm and content mood states), indicating PA throughout the workday should be encouraged as it may have beneficial effects on mental wellbeing and cognitive performance. In contrast to guidelines advising increasing light-intensity PA in the workplace, only moderate-intensity PA at work was positively associated with working memory, possibly indicating this higher intensity of PA should be encouraged during work hours to positively influence cognitive performance in desk workers. Study two aimed to determine the acute effects of a prolonged sitting period on cerebrovascular function, cognition and mood in healthy desk workers. Uninterrupted sitting for six hours reduced CBF and impaired aspects of CA but had no effect on CVR. Decreases in positive affect, and the alert and content mood states were also observed, but these were not related to the concurrent changes in cerebrovascular function. There was no change in cognition following prolonged sitting. Results may have important implications for the long-term mental and physical health of individuals who are repeatedly exposed to periods of uninterrupted sitting. Study three assessed the acute effects of breaking up sitting time on cerebrovascular function in healthy desk workers using two different walking break strategies. The decrease in CBF and CA observed following four hours of uninterrupted sitting was prevented using frequent, short duration walking breaks rather than less frequent, longer duration walking breaks. Results further demonstrate that prolonged uninterrupted sitting impairs cerebrovascular function and suggest that the frequency of the breaks used to interrupt sitting is an important component to preserve aspects of function. In contrast, both walking break strategies caused a larger increase in CVR compared to prolonged sitting. This indicates that, for this aspect of cerebrovascular function, any duration or frequency of PA may have acute benefits. Study four assessed whether using a computer-based prompting software designed to break up prolonged sitting at work altered cerebrovascular function, cognition and mood in healthy office workers. Following the intervention, workplace sitting was reduced and replaced predominantly by increased time spent standing. This reduction in sitting improved aspects of CA but had no influence on other measures of cerebrovascular function, cognition or mood. Results provide preliminary evidence that long-term reductions in SB may improve aspects of cerebrovascular function. Overall, the major findings of this thesis are that prolonged, uninterrupted sitting acutely impairs aspects of cerebrovascular function, however this can be prevented by breaking up sitting with short duration, regular walking breaks. Prolonged sitting also acutely impairs aspects of mood but not cognition. Taken together this thesis provides the first evidence that SB negatively effects cerebrovascular function and further research should explore whether this leads to heightened cerebrovascular disease risk.