Cerebrovascular reactivity (CVR) is one of three regulatory mechanisms to maintain adequate cerebral blood flow (CBF): autoregulation, neurovascular coupling (NVC) and cerebrovascular reactivity (CVR). Autoregulation and NVC have been implicated in blunted responses following an acute glucose load in the context of both healthy individuals and those with metabolic diseases. However, it has yet to be demonstrated if CVR magnitude changes in response to acute glucose loading in healthy participants. The aim of this study was to elucidate the effects of acute hyperglycemia on CVR to increases in carbon dioxide (CO2). We hypothesized that acute glucose loading would blunt the magnitude of the cerebrovascular response to increases in CO2 during rebreathing. 23 healthy participants were recruited and subjected to two separate hyperoxic CO2 rebreathing trials: fasted, and 30-min following ingestion of a standard 300 mL, 75g glucose drink. Blood glucose levels were tested before and after glucose loading, and the difference between these was significant (P <0.0001). CVR was quantified via linear regression during CO2 rebreathing, with the average CVR slope decreasing from the fasted state (1.37±0.5 cm/s/mmHg) to glucose loaded state (1.04±0.6 cm/s/mmHg; P=0.005). This data suggests that relative hyperglycemia significantly blunts the regulatory mechanisms underlying CVR to CO2, and these results could have implications for those suffering from metabolic disorders like diabetes and populations who regularly consume high carbohydrates diets.