A composition contains at least one of homovanillyl alcohol (HVA) or its previously unidentified isomer (isoHVA). Additionally or alternatively, the composition contains a precursor of HVA and/or isoHVA (e.g., hydroxytyrosol, oleuropein aglycone, oleuropein, demethyloleuropein, oleuroside, verbascoside or mixtures thereof) and also contains at least one probiotic and/or at least one enzyme which convert the precursor to HVA and/or isoHVA