Introduction Observational evidence indicates that polyphenol-rich foods, in particular berries and dark chocolate, have the potential to influence cardiovascular disease (CVD) risk.There are few polyphenol dietary intervention studies of sufficiently robust design that assess the effect of polyphenol-rich foods on a range of cardiovascular endpoints in hypertensive patients.The aim of this study was to investigate the effect of increasing overall polyphenol dietary intake on microvascular function and other markers of cardiovascular risk in hypertensive participants.

Methodology All participants commenced with a 4-week run-in phase, during which they were asked to exclude berries and dark chocolate and consume <2 portions of FandV.Subjects were then randomised to continue with the low polyphenol diet for a further 8 weeks, or to consume a high polyphenol diet of 6 portions fruit and vegetables (FandV) (including one portion of berries/day) and 50 g of dark chocolate.Endothelium-dependent and –independent vasodilator responses were assessed by venous occlusion plethysmography.Compliance was assessed with 4-day food diaries and biochemical markers including vitamin C, carotenoids and epicatechin.Other measures of cardiovascular risk included systolic blood pressure (SBP), lipid profile, hsCRP and PAI-1.

Results A total of 99 volunteers completed the study, 6 were excluded from analysis due to elevated hsCRP.Between group comparison of maximum % response to acetylcholine (Ach) was significantly improved in the high polyphenol group (p = 0.02). Results were re-analysed with polyphenol-rich foods as a continuous variable, which revealed an absolute increase in the maximum response to Ach of 14.0% (p = 0.008) with an extra daily portion of FandV, and 112.5% (p = 0.020) with an extra daily portion of dark chocolate.There was no significant between group change in response to sodium nitroprusside.

There was a strong trend in favour of a reduction in SBP (p = 0.059), as well as a significant decrease in total cholesterol (p = 0.042), in the high polyphenol group. PAI-1 and hsCRP did not improve with a polyphenol-rich diet, though there was a significant decrease in hsCRP in the low polyphenol group (p = 0.026).There was a significant increase in the high polyphenol group on between group comparison of vitamin C (p < 0.001), carotenoids (p < 0.001 for all except lycopene, p = 0.098) and epicatechin (p = 0.008), indicating good dietary compliance.

Conclusions This work has shown that polyphenol-rich foods can effect a significant improvement in endothelium-dependent vasodilation following an 8-week intervention in hypertensive participants. These findings suggest that a well-tolerated, simple lifestyle modification can have a significant positive effect on markers of cardiovascular risk.