Diets high in plant foods are protective of health. In particular, plant based diets appear to be protective of cardiovascular disease. Plants produce polyphenolic substances as secondary metabolites and many of these chemicals are biologically active in humans. The absorption and metabolism of polyphenolic substances in complex, but generally it is thought that polyphenolic metabolites are partly responsible for the cardioprotective effects of plants. The way that polyphenols can protect from cardiovascular disease has been extensively studied and a role for some polyphenols in preventing endothelial dysfunction, inhibiting platelet aggregation, and modulating lipid metabolism has been identified. Polyphenols are strong antioxidants and it is in this role that they are thought to protect the enzyme nitric oxide synthase from destruction by free radicals which in turn increases vascular concentrations of nitric oxide, a know vasodilating agent. As nitric oxide deficiency is thought to lead to endothelial dysfunction and ultimately cardiovascular disease, polyphenols may provide significant cardioprotection.
Blueberries are a good source of a group of polyphenols called flavonoids. In particular, blueberries contain high amounts of flavonoids called anthocyanins that are concentrated in the skins. The ability of blueberry polyphenols to produce cardioprotective effects has been tested in humans using double blind, placebo controlled, crossover trials. For example in one study1, researchers fed 21 health men a drink containing either 0, 766, 1278 or 1791 mg of blueberry polyphenols and measured plasma levels of flavonoids and the degree of flow mediated dilation at 1, 2, 4 and 6 hours after consumption. The results showed that there was a biphasic increase in the degree of flow mediated dilation (the amount of dilation caused in response to blood flow) at between 1 and 2 hours and also at 6 hours after consumption of the blueberry, but not the control drink. However, the blueberry treatments all produced the same degree of change, suggesting that 766 mg of blueberry polyphenols was enough to cause the maximum physiological response.
Because the 766 mg dose appeared to be as beneficial as the higher 1278 and 1791 mg doses, the researchers performed a further study at assess the dose response effects of blueberry polyphenols. In this experiment they administered either 0, 319, 637, 766 or 1791 mg of blueberry polyphenols and then monitored changes to flow mediated dilation for 1 hour post consumption. The results showed that for up to 1 hour, benefits to flow mediated dilation were seen in the subjects in a dose response manner up to the 766 mg dose, but after this no further improvements in flow were seen. The improvements in the degree of flow mediated dilation mirrored the increases in the amount of polyphenolic metabolite detected in the plasma of the subjects. Interestingly the 1-2 hour improvements in flow mediated dilation were associated with a different set of flavonoid metabolites that the 6 hour improvements, suggesting that the polyphenol profile and absorption characteristics of blueberries determines the cardioprotective improvements in flow mediated dilation.
Dr Robert Barrington’s Nutritional Recommendation: Blueberries appear to show particularly beneficial effects against the development of metabolic changes associated with cardiovascular disease. These effects include the ability of blueberries to improve flow mediated dilation and this in turn allows them to reduce blood pressure. Decreases in the amount of NADPH oxidase, a known generator of superoxide radicals, suggest that the benefits of the blueberries are because they increase the antioxidant defence of vascular tissues and this in turn increases levels of the blood vessel dilating agent nitric oxide. Blueberries therefore improve vascular function through antioxidant mechanisms and this prevents the development of endothelial dysfunction. Polyphenolic substances in other foods such as cocoa may have similar beneficial effects on endothelial function. Incorporating plant foods that are rich in polyphenols is therefore an important strategy in preventing cardiovascular disease.
RdB
