Urinary excretion of olive oil phenols and their metabolites in humans.

We have recently demonstrated, in humans, the bioavailability of hydroxytyrosol (3,4-dihydroxyphenylethanol; HT), one of the major antioxidant components of virgin olive oil. In particular, we reported that this compound is present in lipoproteins involved in atherosclerotic processes and is excreted in the urine mainly as glucuronide-conjugate. The aim of the present study was to elucidate, in humans, the metabolic fate of HT after ingestion of virgin olive oil. After administration of virgin olive oil, 24-hour urine collections of healthy volunteers were prepared for gas chromatography-mass spectrometry analyses in order to identify and quantify HT and its metabolites homovanillic alcohol (HVA1c) and homovanillic acid (HVA). The results indicate that this compound undergoes the action of catechol-O-methyl transferase (COMT), enzymes involved in the catecholamine catabolism, resulting in an enhanced excretion of HVA1c. We also found a significant increase of HVA, indicating an oxidation of the ethanolic residue of HT and/or of HVA1c in humans. The excretion of both metabolites significantly correlated with the dose of administered HT. Copyright 2001 by W.B. Saunders Company