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:In fact, insulin itself was proven to be a growth factor by its affinitywith the insulin receptor and insulin-like growth factor receptors, and stimulatory for the synthesis and release of adipokines (such as leptin) in adipose tissue [40].
Category: