Polyphenols are found in more than 700 foods, primarily in most fruits and vegetables, herbs and spices and even nuts and cocoa products. Many are considered superfoods. Top providers are foods like blueberries, apricots, grapes, olives and olive oil, artichoke, herbs such as oregano, peppermint and cloves, with nuts and seeds like walnuts, almonds and flaxseed, green tea and even dark chocolate in the top 30
The anti-cancer effect of polyphenols works because of their anti-oxidant properties, which protect the DNA from oxidative damage from carcinogens. Polyphenols can also actually kill cancer cells and inhibiting their proliferation. ... Polyphenols are anti-inflammatory and can also help prevent cancer from forming. 2
Read more about Polyphenols
http://file.scirp.org/pdf/FNS_2014061815351482.pdf
Also potential in covid study https://www.sciencedirect.com/science/article/pii/S2214799320300679
This is a very interesting aspect on the url above.
Figure 1. Effect of polyphenols on different steps of the SARS-CoV-2 life cycle. Polyphenols potentially inhibit binding of SARS-CoV-2 spike protein to host-cell receptor ACE2, prevent viral entry into the host cell, and inhibit viral RNA replication and protein processing.