Effects of a 'healthy' diet and of acute and long-term vitamin C on vascular function in healthy older subjects

Abstract

Objective: Aging is associated with endothelial dysfunction. We studied the acute and longer-term effects of vitamin C compared to a 'Mediterranean-type' diet on endothelial function in healthy older subjects.

Methods: Bilateral venous occlusion plethysmography was used to measure forearm blood flow in subjects aged 57-80 years. Responses to cumulative intra-arterial doses of the endothelium-dependent dilator bradykinin (BK; n=56; 20, 40, 80 pmol/min) and the nitric oxide donor glyceryl trinitrate (GTN; n=54; 4, 8, 16 nmol/min), were determined alone and in the presence of vitamin C (25 mg/min). We then randomised 54 subjects to a 'healthy' diet (n=18), vitamin C (1 g/day; n=18) or placebo for 6 weeks and reassessed endothelial and smooth muscle function.

Results: Acute intra-arterial vitamin C did not alter dilatation to BK or GTN. Similar increases in plasma vitamin C occurred on oral vitamin C (83+/-4 to 135+/-8 micromol/l) and 'healthy' diet (84+/-5 to 135+/-27 micromol/l; P<0.01 for both), with no change seen on placebo. Treatment with a 'healthy' diet but not oral vitamin C improved endothelium-dependent (P=0.043) and endothelium-independent dilatation (P=0.011).

Conclusions: A 'Mediterranean-type' diet rich in vitamin C improves vascular function. Neither acute intra-arterial nor sustained administration of oral vitamin C improves vascular function in healthy older subjects.