1. A method for preserving, restoring, or affecting pancreatic beta cell function in a subject comprising: (a) electrically stimulating C-afferent sensory nerve fibers innervating pancreatic beta cells in a subject, in which said electrical stimulation serves to modulate secretion of calcitonin gene-related peptide (CGRP) from said C-afferent sensory nerve fibers; (b) determining a level of a biomarker in said subject; and (c) repeating said electrical stimulation as a function of the level of said biomarker.