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NutrInsight • Do we need dietary polyphenols for health?
In a mouse prostate cancer model, Siddiqui et al, have also demonstrated that tea polyphenols inhibit the NFkB signalling, which is a central control for inflammatory conditions [Siddiqui et al., 2008]. In the same way, cocoa polyphenols are able to reduce NFkB activation in different cell model [Vazquez-Agell et al., 2011].
3.3 Increasing nitric oxide bioavailability
There is now quite convincing evidence that flavanols (epicatechin) and probably other polyphenols also increase NO bioavailability [Schroeter et al., 2006] with increased plasma NO metabolites coinciding with improved FMD. So how do polyphenols improve NO bioavailability?
There are a number of possibilities and several have been shown to be plausible. These include (but are not limited to) inhibition of NADPH oxidase (NOX) [Steffen et al., 2008] and increase in levels of endothelial nitric oxide synthase (eNOS) or its activation [Schini-Kerth et al., 2010].
3.4 Prebioticeffects
Increasing evidence also suggests that polyphenols can modulate the microbiota in the large intestine, potentially acting as prebiotics, thus influencing the immune response and modulating some aspects of lipid metabolism.
Recently, Tzounis et al [Tzounis et al., 2011] have shown the ability of cocoa polyphenols to modulate gut microbiota. In this trial, high-flavanol diet led to an increase in enteric Bifidobacteria, Enterococcus, and Lactobacilli whereas Clostridia were decreased. This kind of change in microbiota composition is thought to be beneficial for health [Saulnier et al., 2009]. Notably, bacterial changes was associated with a change in C-reactive protein concentration, a circulating marker of inflammation.
3.5 Metal chelation
Finally, one often overlooked mechanism of action of polyphenols, in particular of ortho-diphenols, is metal chelation [Mladenka et al., 2010]. Metals are normally circulated in blood and are also stored as part of other molecules. Examples are iron in hemoglobin and copper in ceruloplasmin. Unbound metals are toxic since they catalyse oxidative reactions, e.g. Fenton’s formation of free radicals. Metal chelation by polyphenols, e.g. during food digestion when large amounts of peroxides are formed, lessens the risk of oxidative damage [Kanner & Lapidot, 2001].
Therefore, consumption of polyphenol-rich foods, e.g. extra virgin olive oil [Visioli et al., 1995] with meals might lessen oxidative damage independent of their mere antioxidant action.
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