Prophylactic
insulin treatment is effective in preventing diabetes in animal models of
insulin-dependent diabetes mellitus (
IDDM) but the safety of such preventive treatment in prediabetic human subjects remains unclear;
insulin is a potential
autoantigen that could accelerate beta-cell decompensation and onset of
IDDM. We have investigated whether
insulin treatment of non-diabetic subjects increases the risk of subsequent development of diabetes in a retrospective study of Danish patients who received
insulin-shock treatment for
psychiatric disorders. Mean age of the 481 patients at
insulin-shock treatment was 32.6 (range 12.9-69.6) years. The patients received 59 (6-200)
injections of 78 (16-261) IU bovine/
porcine insulin. Hospital records provided an average of 22.0 (0.6-51.2) years' observation. During the observation time,
IDDM developed in only 1 patient; 1.3 cases would be expected from Danish incidence data (p = 0.75). Similarly, there was no significant difference between the observed number of cases of
non-insulin-dependent diabetes mellitus (
NIDDM) and the number expected from Danish prevalence data (12 vs 10.2; p = 0.45). We collected blood samples from 27 of the patients. All but 2 (who had previously diagnosed
NIDDM) had normal fasting
blood glucose and plasma
insulin concentrations, none had islet-cell
antibodies, and only 2 had detectable
insulin antibodies. Thus, the risk of diabetes was not increased by the use of many
insulin injections in these non-diabetic subjects. We conclude that clinical trials on prevention of
IDDM by prophylactic
insulin treatment can be regarded as safe.