Is a higher ingestion of phenolic compounds the best dietary strategy? A scientific opinion on the deleterious effects of polyphenols in vivo

Background: Phenolic compounds have been studied for a variety number of bioactivities using in vitro, ex vivo, and in vivo protocols. Most of the studies dealing with phenolic compounds deal with in vitro antioxidant, an tihypertensive, anti-inflammatory, antipyretic, antihemolytic effects in human erythrocytes, hypolipidemic, and antiproliferative activities. Scope and approach: Companies have used the overall understanding of the beneficial effects of polyphenols to develop “functional” foods and ingredients. However, the main question that arises is still the target of warm discussions: Is the higher ingestion of phenolic compounds the best dietary strategy? Our commentary focuses on this question and we list some examples in which phenolic compounds show deleterious effects in vivo. Key findings and conclusions: Two main conclusions arise: (i) any presumption of “functional effects” based on test-tube studies should be avoided as these results do not represent the real biological effect in humans; (ii) at high concentrations and in specific populations, polyphenols may have several potential adverse health effects presumably associated to their pro-oxidative capacity. All in one, the dietary supplementation containing high doses of polyphenols should be well justified in each case until a consensus is reached supported on medical, nutritional and toxicological data.