The best replacement for flavonoids is polyphenols.

The best alternatives to flavonoids are rated as following:
★★★★★  polyphenols
★★★★★  bioflavonoids
★★★  flavonols

Your alternative for flavonoids is not listed? Suggest!
Speaking about flavonoids, one probably shouldn't forget about vitamin c.

Other search terms related to flavonoids and their ratings are:
★★★★★ vitamin c
You have in mind a companion for flavonoids and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of flavonoids in all years. Click on graph for more.
flavonoids
polyphenols
bioflavonoids