Flavonoids

Chemists sort flavonoids into subgroups by where one ring of the molecule (the B ring) attaches to another (the C ring), and by the C ring's double bonds and degree of oxidation [1]. The subgroups include flavones, flavonols, flavanones, flavanonols, flavanols (also called catechins), anthocyanins and chalcones [1].

The names are easy to confuse. Flavonols, spelled with an "o", and flavanols, spelled with an "a", are separate subgroups in that list [1]. Cocoa, for example, is rich in the flavanol subclass [2], so a cocoa paper that says "flavanols" is describing one subgroup, not flavonoids as a whole.

Flavonoids belong to the plant secondary metabolites, and they are widely found in fruits, vegetables and certain beverages [1]. A 2016 overview noted that the working mechanisms of flavonoids are still not properly understood [1].

Because "flavonoids" covers several subgroups with different structures, it helps to note which subgroup or single compound a study actually measured or gave, and how much.

Flavonoid content is also a common way to specify an herbal extract. Health Canada's ginkgo monograph, for instance, describes extracts standardized to 22-27% flavonoid glycosides and 5-7% terpene lactones [3]. A figure like that describes what is in the product; it says nothing on its own about effects, which are graded on each compound page, such as Ginkgo biloba and Cocoa flavanols.

Flavonoids have a polyphenolic structure [1], so they also fall under the wider label "polyphenols". When a paper pools "polyphenol" studies, check whether flavonoids were the only compounds included.

• Flavanols
• Polyphenols
• Standardized extract
• Botanical extract