The effects of an oral glucose challenge on cardiovascular responses to mental stress

Consumption of carbohydrates has been demonstrated to alter resting cardiovascular function and cardiovascular reactions to mental stress (known as cardiovascular reactivity). Previous investigations of the effects of acute carbohydrate administration on cardiovascular reactivity suggest that ingestion of glucose followed by mental stress alters hemodynamic responses by attenuating elevations in cardiac output and increasing total peripheral resistance. However, these prior investigations have utilized tasks which have limited generalizability to real-life stressors and were conducted with participants in a recumbent position. The present study investigated the effects of oral glucose administration on resting cardiovascular parameters and cardiovascular reactivity in twenty four seated healthy male college students. Interpersonal speech and anger recall tasks were utilized to elicit a greater emotional response than those used in previous studies and to more closely mirror stressors encountered in everyday life. Ratings of affect, task engagement, and hunger were assessed to determine whether these constructs might be involved in promoting cardiovascular responses. During the post-prandial baseline period, ingestion of glucose resulted in significantly increased systolic blood pressure, heart rate, and cardiac index and a greater decrease in cardiac pre-ejection period than placebo. However, there was no significant effect of oral glucose administration on cardiovascular reactivity. There were no effects of glucose on affect, task engagement or hunger ratings at post-prandial baseline, however, during the tasks glucose was associated with increases in positive affect, negative affect, and task engagement, as well as decreases in hunger ratings. In comparison, consumption of the placebo was associated with decreases in positive affect, negative affect, and task engagement, and increases in hunger ratings during the tasks. These results suggest that oral glucose administration evokes a potent cardiac response at rest, but does not influence cardiovascular responses to emotionally-evocative mental stress. The effects of oral glucose administration on cardiovascular reactivity may therefore be limited to mental stressors that lack a strong emotional or interpersonal component and/or these effects may be limited to situations where stress is encountered in a recumbent position. Results of the current study add to the literature by enhancing the ecological validity of the mental stressors utilized. Further, the present investigation showed that the association of glucose to cardiovascular function can be effectively studied less invasively with impedance cardiography. The present study also extended previous work in this area by demonstrating that acute glucose administration increases positive and negative affect, and task engagement while decreasing hunger ratings. It is concluded that, for healthy young men, prior ingestion of glucose may not enhance cardiovascular responses to all types of stressors and therefore may not increase risk for cardiovascular disease. However, the increase in resting cardiovascular parameters following glucose administration may have negative cardiovascular health consequences.