Refer to the input text as context and select the correct relationship between 'beta cell' and 'insulin' from the available options.
Options: founded by, parent organization, developer, product/material produced

No new safety signals or data were presented at this year's ADA conference, but data was presented that confirmed the preservation and restoration of beta cell function as determined by C-peptide, which is a measure of a person's own insulin production.
product/material produced