The Biological Relevance of Direct Antioxidant Effects of Polyphenols for Cardiovascular Health in Humans Is Not Established1–4

Abstract

Human studies provide evidence for beneficial effects of polyphenol-rich foods on cardiovascular health. The antioxidant activity of polyphenols potentially explains these effects, but is the antioxidant activity a reliable predictor for these effects? An International Life Sciences Institute Europe working group addressed this question and explored the potential of antioxidant claims for polyphenols in relation to cardiovascular health by using the so-called Process for the Assessment of Scientific Support for Claims on Foods project criteria. In this process, analytical aspects of polyphenols, their occurrence in foods, dietary intake, and bioavailability were reviewed. Human studies on polyphenols and cardiovascular health were reviewed together with methods for biomarkers of oxidative damage and total antioxidant capacity (TAC). In retrospective studies, F2-isoprostanes and oxidized LDL, the most reliable biomarkers of lipid peroxidation, and measures for TAC showed the expected differences between cardiovascular disease patients and healthy controls, but prospective studies are lacking, and a causal relationship between these biomarkers and cardiovascular health could not be established. Therefore, the physiological relevance of a potential change in these biomarkers is unclear. We found limited evidence that some types of polyphenol-rich products modify these biomarkers in humans. A direct antioxidant effect of polyphenols in vivo is questionable, however, because concentrations in blood are low compared with other antioxidants and extensive metabolism following ingestion lowers their antioxidant activity. Therefore, the biological relevance of direct antioxidant effects of polyphenols for cardiovascular health could not be established. Overall, although some polyphenol-rich foods exert beneficial effects on some biomarkers of cardiovascular health, there is no evidence that this is caused by improvements in antioxidant function biomarkers (oxidative damage or antioxidant capacity).

Free radical scavenging actions of threeTrifoliumspecies in the protection of blood plasma antioxidant capacityin vitro

“…The biological relevance of direct antioxidant effects of polyphenols for cardiovascular health in humans is not fully established, and the beneficial effect of polyphenol-rich diet seems to be rather an effects of their multifaceted bioactivity (Hollman et al, 2011). To the contrary, antioxidant properties still remain an important factor contributing to the favorable effects of polyphenolic compounds on human health.…”

Evidence for a protective effect of polyphenols-containing foods on cardiovascular health: an update for clinicians

“…Furthermore, recently, experts from an International Life Sciences Institute Europe working group found limited evidence concerning the impact of polyphenol-rich products on biomarkers of oxidative stress in humans. This group concluded that the biological relevance of direct antioxidant effects of polyphenols for cardiovascular health could not be established [Hollman et al 2011]. According to the recent literature, the mechanisms by which polyphenols express their beneficial properties appear to involve their interaction with molecular signalling pathways and related machinery that regulate cellular processes such as inflammation [Gonzalez-Gallego et al 2010;Gonzalez et al 2011].…”

The Occurrence, Fate and Biological Activities ofC-glycosyl Flavonoids in the Human Diet

“…As such, this review will principally focus on literature describing the defined bioactivities of enriched or purified Cglycosyl flavonoid fractions only. Additionally, direct antioxidant effects described in vitro will be omitted due to the lack of significant correlation between in vitro antioxidant capacity and in vivo plasma antioxidant capacity for some tested C-glycosyl flavonoids (Breiter et al, 2011;Hollman et al, 2011;Mladenka et al, 2010).…”