Effects of oat phenolic acids and avenanthramides on cardiovascular health

Abstract

High consumption of wholegrains is associated with lower risk of cardiovascular disease. Studies suggested that regular consumption of oats lowers blood cholesterol and improves post-prandial glycaemic control. Some of these benefits were shown to be partly mediated by β-glucan soluble fiber. However, oats are also a source of bioactive phenolics, including the most abundant ferulic acid and avenanthramides. Circulating phenolic acids from other foods/beverages such as blueberries and champagne were shown to exert health benefits via enhancing nitric oxide bioavailability to the vascular endothelium, research to date has not yet established whether oat phenolics may also contribute to cardiovascular health benefits of oats. Therefore, this thesis investigates the potential beneficial effects of oat phenolics on human cardiovascular system. Composition and content of a variety of commercial oat products were analyzed and average amounts delivered to the consumer in a portion was estimated as follows: 15.79-25.05 mg /40 g for oat products and 16.7 mg /11 g for oat bran concentrate. While the compositions and concentrations of the components in the different products were broadly similar, most abundant phenolic acid was shown to be ferulic acid. The findings suggested that commercial oat products are a source of phenolic acids and avenanthramides and these data informed following clinical work about human dietary intake levels of these compounds in oats. A 2-arm, randomized, crossover, single-blind acute clinical trial was conducted with 16 pre and stage 1 hypertensive men. Consumption of 90.2g of oats containing 50mg of phenolics resulted in a small non-significant improvement in flow mediated dilatation (FMD) at 1h and significant changes in both endothelium dependent and independent microvascular function relative to control at 2h. Inter-individual variability in phenolic absorption observed and changes in microvascular function at 2h were positively correlated with the blood concentration of phenolic acid metabolites including ferulic acid glucuronides and sulfates. However, no other changes in blood pressure (BP) and NADPH oxidase activity were observed between treatments. In a 3-arm, randomized , crossover, double-blind chronic trial , 28 pre and stage 1 hypertensive subjects consumed either a high (68.1 mg of phenolics) or moderate (38.9 mg of phenolics) phenolic acid and avenanthramide containing oat diet, or fibre matched control diet. 24-hour SBP, night time SBP and DBP decreased significantly and FMD response improved non-significantly following the consumption of high phenolic oats. There was also small non-significant improvements in endothelial dependent and independent microvascular reactivity and non-significant reductions in total and LDL-cholesterol following the consumption of high and moderate phenolics but no change observed in the numbers of circulating extracellular vesicles. These data suggest that consumption of oat phenolics may improve cardiovascular health and strengthen the evidence about health benefits of oats.