Vitamin C prevents attenuation of flow‐mediated dilation due to acutely altered SR patterns

Abstract

Alterations of normal shear rate (SR) patterns at rest impair flow‐mediated dilation (FMD), possibly due to augmented oxidative stress. We tested the hypothesis that the antioxidant vitamin C would prevent the attenuation of brachial artery FMD following a period of altered SR patterns. Twelve lean healthy men (26.3 ± 3.1 years) participated in two trials. One arm was exposed to altered SR profiles using 60 mm Hg of forearm cuff compression for 30 min while the contralateral arm served as the control. Subjects ingested 500 mg capsules of vitamin C or placebo capsules 90 min and 120 min prior to cuff compression in a randomized double‐blind cross‐over design. There were no differences in baseline FMD or antegrade, retrograde, mean or oscillatory SR. For both trials antegrade SR was unchanged in both arms (P > 0.10). Retrograde (P < 0.01) and oscillatory SR (P < 0.01) increased and mean SR (P = 0.01) decreased in the compression arm with no differences between trials (P > 0.23). FMD was unchanged in the control arm in both trials (P > 0.19). FMD decreased following compression + placebo (pre 5.2 ± 1.4% vs. post 3.5 ± 1.4%) (P < 0.01), but remained unchanged following compression + vitamin C (pre 5.3 ± 2.4% vs. post 5.7 ± 2.6%) (P > 0.46). These data demonstrate that acute vitamin C supplementation prevents the attenuation of FMD following altered SR profiles, which indicates that oxidative stress may contribute to the attenuated FMD response.