Effect of ascorbic acid treatment on conduit vessel endothelial dysfunction in patients with hypertension

Abstract

Hypertension is associated with low plasma ascorbic acid levels and impaired endothelial function. Recent evidence suggests that increased vascular oxidative stress contributes to the pathophysiology of endothelial dysfunction and hypertension. We recently showed that chronic oral ascorbic acid therapy lowers blood pressure in hypertensive patients. We hypothesized that it would also improve endothelial vasomotor function. In a randomized, double-blind, placebo-controlled study, we examined the effect of acute (2 g po) and chronic (500 mg/day for 1 mo) ascorbic acid treatment on brachial artery flow-mediated dilation in 39 patients with hypertension. Compared with 82 age- and gender-matched normotensive controls, these patients had impaired endothelium-dependent, flow-mediated dilation of the brachial artery [8.9 +/- 6.1 vs. 11.2 +/- 5.7% (SD), P < 0.04]. After therapy, plasma ascorbic acid concentrations increased acutely from 50 +/- 12 to 149 +/- 51 micromol/l and were maintained at 99 +/- 33 micromol/l with chronic treatment (both P < 0.001). As previously reported, chronic ascorbic acid therapy reduced systolic and mean blood pressure in these patients. However, acute or chronic ascorbic acid treatment had no effect on brachial artery endothelium-dependent, flow-mediated dilation or on endothelium-independent, nitroglycerin-mediated dilation. These results demonstrate that conduit vessel endothelial dysfunction secondary to hypertension is not reversed by acute or chronic treatment with oral ascorbic acid. The effects of this treatment on resistance vessel vasomotor function warrant further investigation.

Drug Treatment of Hypertension: Focus on Vascular Health

“…Importantly, there was no improvement in forearm vascular responses to the endothelium-independent vasodilator sodium nitroprusside, which suggests that the beneficial effects of fruit and vegetable intake are related to protective effects on the endothelium 156 . The data from this study are in contrast to forearm plethysmography studies that assessed the effect of ascorbic acid on forearm vascular responses and suggest that a balanced, pragmatic approach that considers whole food and dietary patterns may be the best means of improving the overall vascular phenotype of patients with hypertension 156,[178][179][180] . Increased fruit and vegetable consumption may also make patients more likely to adopt other favourable dietary modifications, such as reduced salt and fat consumption.…”

Reactive oxygen species and vascular biology: implications in human hypertension

“…[21][22][23] It is still unclear whether oxidative stress causes hypertension in humans and only a few small clinical studies showed a blood pressure-lowering effect of anti-oxidants, [24][25][26] with most large antioxidant clinical trials failing to demonstrate any cardiovascular benefit and blood pressure lowering. [27][28][29] Nevertheless, what is evident is that oxidative stress has a critical role in the molecular mechanisms associated with cardiovascular and renal injury in hypertension and that hypertension itself can contribute to oxidative stress.…”

Is vitamin C an effective antihypertensive supplement? A review and analysis of the literature

“…Thirteen trials [8][9][10][11][12][13][14][15][16][17][18][19][20] making up 14 separate group populations were identified and analyzed providing a total pooled population of 284 hypertensive patients (52% female), with a weighted mean age of 58.8 ± 9.5 years and a weighted mean body mass index of 28.5 ± 1.9 Kg/m 2 . Median vitamin C dose and study intervention duration was 500mg/day and 6 weeks respectively ( Table 1).…”

“…Clinical trials performed to assess the effect of vitamin C supplementation on blood pressure in hypertensive individuals have met with mixed results. [8][9][10][11][12][13][14][15][16][17][18][19][20] In 1997 Ness et al concluded that there were too few clinical trials, and those reported at that time were generally too small and too varied to provide confirmatory evidence for a casual relationship. 21 This study was undertaken in order to evaluate the current clinical evidence that vitamin C supplementation lowers both systolic and diastolic blood pressure in hypertensive individuals, and to also review the hypothesized mechanisms of action.…”