In AIP attacks there is an escalating metabolic chain reaction leading to heme deficiency and increased levels of porphyrin precursors. This reaction is inhibited by treatment with glucose or heme arginate. In a population-based study in the two most northerly counties of Sweden (Norrbotten and VÃ¤sterbotten), out of 319 patients > 18 years of age with DNA-verified AIP, 16 had type-2 diabetes. None of the 16 patients showed AIP symptoms after the onset of their diabetes. Three patients had suffered recurrent, severe attacks for many years, but after onset of diabetes their ALA and PBG levels decreased and the AIP symptoms resolved, to the relief of the patients. In a study of the 30 AIP patients with hepatocellular carcinoma (HCC) none had diabetes. This implies that diabetic metabolism may prevent the development of HCC in patients with AIP. The prevalence of AIP patients with diabetes was lower than the prevalence of diabetic patients in the general population. This study shows that diabetes mellitus may be beneficial for patients with severe AIP.