Yielding 2.5% Anthocyanins.

Only a small percentage of ingested anthocyanins are absorbed intact. The rest reach the colon where microbial enzymes cleave the sugar and open the ring, producing phenolic acids such as protocatechuic acid that appear in blood at far higher concentrations than the parent pigment. Which bacteria a person carries therefore shapes what they actually get from an anthocyanin dose.

In aqueous solution ascorbic acid accelerates anthocyanin degradation through a mutual oxidation reaction, an effect long documented in fruit juice chemistry. The two are often co-formulated on the assumption that antioxidants help each other. In a liquid product they can shorten each other's shelf life, though in a dry capsule the reaction has little water to proceed in.

Flavonols such as rutin stack against the flat anthocyanin chromophore, shielding it from water attack at the C2 position and holding it in the coloured flavylium form. This is why anthocyanin colour is more stable in a whole fruit extract than in a purified pigment. The effect is on stability and colour, which is a formulation matter rather than a biological one.

Quercetin and its glycosides travel with anthocyanins in berry extracts and contribute to the copigment complex that stabilises the colour. They also share glucuronidation and sulfation routes after absorption, which means the two can compete for the same conjugating capacity at higher doses. Both aspects are worth noting on a combined product.

Proanthocyanidins are oligomers built from the same flavan-3-ol chemistry, and both classes are largely converted to phenolic acids by colonic bacteria. The overlap means a combined product delivers a wider polyphenol spread but not two independent effects. The final metabolite pool overlaps considerably.

Both classes are studied in relation to small vessel function and both end up as colonic phenolic acid metabolites. Formulators combine them for a broader polyphenol profile. As with grape seed, the metabolic overlap limits how far the effects can genuinely stack.

Lutein is a fat-soluble pigment concentrated in the macula by specific binding proteins. Anthocyanins are water-soluble, poorly absorbed and not retained in ocular tissue in any comparable way. The pairing is a long-standing formulation convention rather than a demonstrated interaction, and it deserves to be described as such.

Zeaxanthin occupies the central macula and is retained there by a specific binding protein. Anthocyanins have no such retention mechanism in the eye. The combination reflects category convention and not a shared route.

The ortho-dihydroxy arrangement on cyanidin and delphinidin binds iron and other transition metals, which is the same chemistry behind polyphenol interference with non-haem iron absorption from tea and berries. Taken in the same dose, a polyphenol-rich extract can lower the absorbed fraction of a non-haem iron supplement. Metal binding also shifts anthocyanin colour, so the interaction shows up visually in a formula.

Anthocyanins associate with pectin in the fruit cell wall, which slows their release in the upper gut and delivers more of them to the colonic bacteria. The result is less intact pigment early and more microbial metabolite later. Whether that is desirable depends on which of the two you consider the active species.

Anthocyanins and other polyphenols coordinate divalent metals including zinc, which can lower the absorbed share when both are taken together. The effect is smaller and less documented than the iron interaction. Spacing the doses by a couple of hours removes the question.