Health effects of phenols and polyphenols

Polyphenols have poor bioavailability, indicating that most of what are consumed are extensively metabolized and excreted.[1][3] Gallic acid and isoflavones may show absorption of about 5%,[1][3] with amounts of catechins (flavan-3-ols), flavanones, and quercetin glucosides even less.[1] The least well-absorbed phenols are the proanthocyanidins, galloylated tea catechins, and anthocyanins.[3]

Due to their potential beneficial effects on pathways related to cognitive function such as inflammation and vasodilation, several types of polyphenol subclasses including blueberries and resveratrol have been investigated as a potential intervention for cognitive outcomes in both healthy adults and those with chronic diseases (e.g. mild cognitive dysfunction and cardiovascular disease).[4][5]

The European Food Safety Authority found that flavonols in cocoa – at doses exceeding 200 mg per day – could contribute to normal function of the vascular endothelium,[6] and olive oil polyphenols (5 mg of hydroxytyrosol and its derivatives (e.g. oleuropein complex and tyrosol) "contribute to the protection of blood lipids from oxidative damage", if consumed daily.[7] Because long-term studies of high polyphenol intake have not been conducted, there is a lack of knowledge about safety or effect on health of intake above levels in a normal diet.[1][8] A 2017 Cochrane review concluded that there is moderate-quality evidence that flavonol-rich cocoa products decrease blood pressure by only 2 mmHg in the short-term, although longer-term studies are needed.[9]

As interpreted by the Linus Pauling Institute[1] and the European Food Safety Authority (EFSA),[2] dietary flavonoids have little or no direct antioxidant food value following digestion.[10] Unlike controlled test tube conditions where antioxidant effects may result when high concentrations of flavonoids are used, the fate of ingested flavonoids in vivo shows they are poorly conserved (less than 5%), with most of what is absorbed existing as chemically-modified metabolites destined for rapid excretion.[1]

As of 2019, there is little evidence that dietary flavonoids lower the risk of cancer.[1]

Phlebotonics of heterogeneous composition, consisting partly of citrus peel extracts (flavonoids, such as hesperidin)) and synthetic compounds, are used to treat chronic venous insufficiency and hemorrhoids.[11] Some are non-prescription dietary supplements, such as Diosmin,[11] while one other – Vasculera (Diosmiplex) – is a prescription medical food intended for treating venous disorders.[12] Their mechanism of action is undefined,[11] and clinical evidence of benefit for using phlebotonics to treat venous diseases is limited.[11]

• Polyphenol
• Polyphenol antioxidant
• Flavonoid