Although anthocyanins have been shown to have antioxidant properties in vitro, there is no evidence for antioxidant effects in humans after consuming foods rich in anthocyanins. Unlike controlled test-tube conditions, the fate of anthocyanins in vivo shows they are poorly conserved (less than 5%), with most of what is absorbed existing as chemically modified metabolites that are excreted rapidly. The increase in antioxidant capacity of blood seen after the consumption of anthocyanin-rich foods may not be caused directly by the anthocyanins in the food, but instead by increased uric acid levels derived from metabolizing flavonoids (anthocyanin parent compounds) in the food. It is possible that metabolites of ingested anthocyanins are reabsorbed in the gastrointestinal tract from where they may enter the blood for systemic distribution and have effects as smaller molecules.
In a 2010 review of scientific evidence concerning the possible health benefits of eating foods claimed to have "antioxidant properties" due to anthocyanins, the European Food Safety Authority concluded that 1) there was no basis for a beneficial antioxidant effect from dietary anthocyanins in humans, 2) there was no evidence of a cause-and-effect relationship between the consumption of anthocyanin-rich foods and protection of DNA, proteins, and lipids from oxidative damage, and 3) there was no evidence generally for consumption of anthocyanin-rich foods having any "antioxidant", "anti-cancer", "anti-aging", or "healthy aging" effects.