Polyphenolic compounds derived from plants are bioavailable in humans and may modulate a number of physiological parameter favourably. This is reflected in epidemiological studies that demonstrate an association between polyphenol consumption and certain health benefits. In particular, polyphenol intake is associated with a reduction in the risk of cardiovascular disease, although the mechanisms for such protective effects are not fully understood. Polyphenols are strong in vitro antioxidants, and one line of evidence suggests that they may maintain this activity in human plasma. Nitric oxide synthase is the enzyme responsible for the production of nitric oxide, a short-lived hormone required for dilation of blood vessels and responsible for blood pressure regulation. Oxidative stress can impair nitric oxide synthase and thus increase blood pressure. Through their antioxidant activity, polyphenols may inhibit this oxidative stress and therefore cause dilation of blood vessels and a reduction in blood pressure.
The blood pressure lowering effects of polyphenols has been reported in a number of recent studies. For example, one group of researchers1 investigated the blood pressure lowering effects of polyphenols by performing a meta-analysis on randomised controlled trials using cocoa powder to affect blood pressure. In particular, the authors assessed the effects of epicatechin, a component of the proanthocyanidins in cocoa, on the systolic and diastolic blood pressure readings of subjects, and determined if a dose response existed. Using data from 16 randomised controlled trials investigating systolic blood pressure and 15 randomised controlled trials investigating diastolic blood pressure, the authors reported that epicatechin showed a dose response effect on blood pressure. An intake of 25 mg epicatechin from cocoa caused a decrease in systolic blood pressure of 4.1 mm Hg and a decrease in diastolic blood pressure of 2 mm Hg.
These results support data from studies investigating the effects of other polyphenols on blood pressure. The authors reported that 25 mg of epicatechin was equivalent to 25 to 30 g of commercially available cocoa, and so this intake is achievable be the general population. A reduction in systolic blood pressure of 2 mm Hg is associated with a 10 % reduction in stroke mortality and a 7 % reduction in ischaemic heart disease in middle aged subjects. Tea has been extensively researched for its protective effect against cardiovascular disease. Tea, like cocoa, is also a rich source of epicatechin, and this may explain the epidemiological effects of tea on blood pressure and its ability to reduce the risk of cardiovascular disease. Diets high in polyphenols, such as the Mediterranean diet, also reduce blood pressure and some evidence (here) suggests that this is because they improve endothelial function through reductions in oxidative stress.
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