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:SphK1 catalyzes the phosphorylation of sphingosine to sphingosine-1phosphate (S1P), thus decreasing the level of pro-apoptosis ceramide and increasing pro-survival S1P production [30].
Category: