Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Experiments in vivo and in vitro show that plant polyphenols enhance intracellular antioxidant defense and anti-inflammatory capacity, therefore they can be used as photo-protective and chemo-preventative agents [4,10,11].
Category: