having the flavone skeleton 2 phenyl chromone 2 phenyl benzopyrone and isomers thereof such as the isoflavones 3 phenyl chromones chalcones 2 cinnamoyl phenols and aurones 2 benzylidene benzofuranones also the anthocyanidins which differ from the flavones by the presence of a pyrylium moiety instead of the pyrone moiety are considered to be included in the flavonoids the hydroxy functions of the flavonoid compounds may be and preferably are partly alkylated or glycosylated as is the case in natural compounds such as anthocyans glycosylated anthocyanidins and glycosylated flavonols among the flavones the flavonols especially the flavonotetraols and higher hydroxylated analogues such as kaempferol quercitin and myrecitin and the methylated analogues such as sinensetin tangeretin and nobiletin as well as the glycosides such as rutin and myricitrin are preferred among the isoflavones daidzein and genistein are examples of preferred compounds and among the anthocyanidins peonidin cyanidin pelargonidin delphinidin petunidin and valvidin are preferred flavanones 2 3 dihydroflavones such as hesperetin and naringin are other preferred flavonoids the use of a mixture of flavonoids such as in natural plant extracts or mixtures of plant e g citrus tea grape extracts is advantageous preferably the flavonoids according to the invention comprise at least 40 of flavonols and at least 10 of anthocyans more preferably at least.