OBJECTIVES: There is previous epidemiological evidence that intake of 
polyphenol-rich foods has been associated with reduced cardiovascular disease 
risk. We aimed to investigate the effect of increasing dietary polyphenol intake 
on microvascular function in hypertensive participants.
METHODS: All participants completed a 4-week run-in phase, consuming <2 portions 
of fruit and vegetables (F&V) daily and avoiding berries and dark chocolate. 
Subjects were then randomised to continue with the low-polyphenol diet for 
8 weeks or to consume a high-polyphenol diet of six portions F&V (including one 
portion of berries/day and 50 g of dark chocolate). Endothelium-dependent 
(acetylcholine, ACh) and endothelium-independent (sodium nitroprusside) 
vasodilator responses were assessed by venous occlusion plethysmography. 
Compliance with the intervention was measured using food diaries and biochemical 
markers.
RESULTS: Final analysis of the primary endpoint was conducted on 92 
participants. Between-group comparison of change in maximum % response to ACh 
revealed a significant improvement in the high-polyphenol group (p=0.02). There 
was a significantly larger increase in vitamin C, carotenoids and epicatechin in 
the high-polyphenol group (between-group difference p<0.001; p<0.001; p=0.008, 
respectively).
CONCLUSIONS: This study has shown that increasing the polyphenol content of the 
diet via consumption of F&V, berries and dark chocolate results in a significant 
improvement in an established marker of cardiovascular risk in hypertensive 
participants.
TRIAL REGISTRATION NUMBER: NCT01319786.