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:Unfortunately, especially in cases of hereditary renal magnesium wasting, normal values for total serum magnesium are hardly achieved by oral substitution without considerable side effects, mainly resulting from the cathartic effects of magnesium salts [2].
Category: