I am finding articles that indicate that very small amounts of C-peptide can protect against diabetes complications in the eyes and kidneys.
In the February, 2009 issue of Diabetes Care there is a report involving a study of 471 Type 1 diabetics. The subjects were born during the 1945-2004 time period and they had been examined one or more times during the years 1994-2004. Beta cell secretion was observed in some of the people who had been diabetic for a long time. It was found that there were fewer instances of microvascular complications among the Type 1 diabetics who had higher fasting C-peptide values. There were 41% fewer instances of microvascular complications among patients whose C-peptide values were at least 0.06. It should be noted that this pattern was not observed with macrovascular complications.
NOTE: Macrovascular diabetes complications include heart disease, stroke, and diseases in the larger arteries of the limbs. Microvascular complications pertain to the smaller blood vessels and include retinopathy, neuropathy and kidney failure.