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Flavonoids have become a bit of a buzz word in recent months. And the more you find out about their unique health benefits, the more you’ll understand why.

In this article we take a closer look at what dietary flavonoids actually are, why everyone’s talking about them (especially at the moment) and how you can be smart about the way you design your diet to make sure it delivers a range of these beneficial compounds.

What flavonoids actually are...

Flavonoids belong to a family of plant compounds called polyphenols.  They are tiny compounds found in foods and drinks of plant origin such as fruits, vegetables, tea, cocoa and wine.  Sometimes you’ll hear them called bioflavonoids but these terms mean pretty much the same thing and are essentially interchangeable.

There are over 5,000 known varieties of flavonoids and they play many different and fascinating roles in plants.  Among many other incredible functions, they protect plants from stresses (eg insects / fungi / wind / heat), act as UV filters and signalling molecules, detoxify harmful substances and work as antimicrobial defence compounds too!1

And when we consume flavonoids in our diets it seems we are fortunate to inherit many of their protective qualities too.  They have been found to have significant antioxidant and free radical-scavenging abilities.  In addition, they have demonstrated anti-inflammatory activity and offer cardiovascular, metabolic, neuroprotective, potential anti-viral benefits and more.2,3

Why everyone’s talking about them (especially at the moment)

Flavonoids have become an area of particular interest due to their potential role in the regulation of inflammation and cytokine expression.

The pathogenicity of Covid-19 is complex and not fully understood.  However excessive inflammation or ‘cytokine storm’ - where the immune system appears to ‘over-react’- is suspected to play a major role in critical cases.

Cytokine storms are not new, they are associated with several diseases, manifest differently in each case and researchers are still trying to work out why some people are at higher risk.

The Sars-CoV-2 virus has been shown to activate the NLRP3 inflammasome – a part of the innate immune system which may lead to uncontrolled release of pro-inflammatory cytokines, and potentially to severe damage of the respiratory epithelium.4-6

Research has demonstrated regulatory effects of some dietary flavonoids on the NLRP3 inflammasome:

In a 2016 review article entitled Natural compounds as regulators of NLRP3 inflammasome-mediated IL-beta production, the authors noted that “EGCG (epigallocatechin gallate) and quercetin are potent inhibitors of NLRP3 inflammasome-mediated IL-beta production, typically acting at more than one element of the involved pathways.”7

In a 2018 study entitled, ‘Flavonoids interfere with NLRP3 inflammasome activation’, the authors noted that “flavonoids are potential therapeutics for NLRP3 inflammasome-associated disorders, and certain flavonoids including apigenin are expected to ameliorate the inflammatory symptoms in autoinflammatory diseases associated with NLRP3 inflammasome activation”.8

A 2014 study demonstrated a potential zinc ionophore activity of flavonoids quercetin and epigallocatechin gallate (EGCG) – thus meaning they could theoretically enhance zinc’s anti-viral effects.9

Numerous studies have demonstrated regulatory effects of specific dietary flavonoids including dihydroquercetin, quercetin, myricetin and apigenin on NLRP3 inflammasome activation.10-14

We’re a way from understanding more fully how individual flavonoids may be utilised in a more targeted way in the current pandemic.  The evidence to date certainly suggests however that including plenty of flavonoids in the daily diet via a colourful variety of plant foods remains great advice to support overall health and immune resilience.

How to increase your intake of dietary flavonoids

1. Eat a rainbow every day

The rainbow has become a visual symbol of hope and appreciation. Take this a step further and think about including every colour of the rainbow from natural plant foods in a daily diet.  This will help to deliver a diverse range of beneficial phytochemicals including flavonoids.

2. Aim high

Most experts will agree that 5-7 servings of vegetables & 2-3 servings of fruit daily is an optimal aim to support immune and overall health.

3. Use this handy table

This is our quick guide to flavonoid-rich foods:

1. Panche AN, Diwan AD et al. Flavonoids: an overview. J Nutr Sci. 2016; 5: e47
2. Kumar S, Pandey AK. Chemistry and biological activities of flavonoids: an overview. The Scientific World Journal. 29 Dec 2013. Article ID 162750
3. https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/flavonoids#figure-4
4. Conti P, Ronconi G et al. Induction of pro-inflammatory cytokines (IL-1 and IL-6) and lung inflammation by Coronavirus-19 (COVI-19 or SARS-CoV-2): anti-inflammatory strategies. J Biol Regul Homeost Agents. 2020;34(2):1.
5. Ding S, Xu S, et al. Modulatory mechanisms of the NLRP3 inflammasomes in diabetes. Biomolecules. 2019;9(12): E850.
6. Chen IY, Moriyama M, et al. Severe acute respiratory syndrome coronavirus viroporin 3a activates the NLRP3 inflammasome. Front Microbiol. 2019; 10: 50.
7. Tozsér J, Benko S. Natural compounds as regulators of NLRP3 inflammasome-mediated IL-1Beta production. Mediators Inflamm. 2016; 2016: 5460302.
8. Lim H, Min DS, et al. Flavonoids interfere with NLRP3 inflammasome activation. Toxicology and Applied Pharmacology. 28 June 2018
9. H. Dabbagh-Bazarbachi. Zinc ionophore activity of quercetin and epigallocatechin-gallate: from hepa 1-6 cells to a liposome model. J Agric Food Chem, 62 (32) (2014), pp. 8085-8093
10. T. Ding, et al. Kidney protection effects of dihydroquercetin on diabetic nephropathy through suppressing ROS and NLRP3 inflammasome. Phytomedicine (41) (2018), p. 45
11. J.-Y. Choe, et al. Quercetin and ascorbic acid suppress fructose-induced NLRP3 inflammasome activation by blocking intracellular shuttling of txnip in human macrophage cell lines. Inflammation, 40 (3) (2017), p. 980
12. H. Chen, et al. Myricetin inhibits NLRP3 inflammasome activation via reduction of ROS-dependent ubiquitination of ASC and promotion of ROS-independent NLRP3 ubiquitination. Toxicol Appl Pharmacol, 365 (2019), p. 19
13. K. Yamagata, et al. Dietary apigenin reduces induction of LOX-1 and NLRP3 expression, leukocyte adhesion, and acetylated low-density lipoprotein uptake in human endothelial cells exposed to trimethylamine-n-oxide. J Cardiovasc Pharmacol 74 (6) (2019), p. 558
14. K. Kaihatsu, et al. Antiviral mechanism of action of epigallocatechin-3- o-gallate and its fatty acid esters Molecules, 23 (10) (2018), p. 2475

Table adapted from https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/flavonoids

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