Ingestion of glucose and Vitamin C affects orthostatic stress-induced cardiovascular responses in young men

Aim: We hypothesized that coadministration of glucose and Vitamin C will reduce the orthostatic tolerance in normal young male volunteers. Materials and Methods: In a randomized controlled crossover fashion, nine nonobese, young men ingested nothing (control), and glucose (75 g) alone and with Vitamin C (1 g) 10 min before standing on 3 separate days of appointment. We measured the supine and standing blood pressure, heart rate, hematocrit, and blood glucose levels. The orthostatic tolerance was evaluated as the time to presyncope during motionless standing or until presyncopal symptoms were observed. Results: During the first 60 min of standing, 89%, 78%, and 0% of patients experienced the presyncopal symptoms when ingested nothing, glucose alone, and glucose + Vitamin C, respectively. Ingesting glucose alone did not affect the orthostatic tolerance (61.4 ± 1.4 vs. 63.0 ± 1.7 min; P > 0.05) while ingesting glucose with Vitamin C significantly improved the orthostatic tolerance (86.6 ± 2.2 vs. 63.0 ± 1.7 min; P < 0.001). Increases in the systolic blood pressure (SBP) and heart rate induced by standing were significantly enhanced when glucose + Vitamin C was ingested, while changes in diastolic blood pressure were not significantly affected. Ingestion of glucose alone or with Vitamin C led to a comparable significant increase in blood glucose levels after standing. However, a significant increase in hematocrit level was observed after standing when glucose + Vitamin C but not when glucose alone was ingested. Conclusion: The present study reveals that the oral glucose loading with Vitamin C ingestion improves the orthostatic tolerance, and the improvement is associated with an enhanced SBP, heart rate, and hematocrit level.