Prevalence of metabolic hyperferritinemia and association between ferritin and insulin resistance in persons with impaired glucose regulation in the HUNT2 population study

BACKGROUND: Several reports have indicated an association between insulin resistance and hyperferritinemia, and a recent consensus statement has suggested the term metabolic hyperferritinemia (MHF) for patients with metabolic syndrome and increased serum ferritin. The objective of this study was to examine the association between serum ferritin levels and insulin resistance in an unselected Norwegian population. METHODS: Two thousand people were randomly selected from the public registry in one municipality in Nord-Trøndelag County, Norway. Of the respondents, 1115 completed a screening glucose tolerance test to determine the prevalence of impaired glucose tolerance (IGT)/type 2 diabetes mellitus (T2DM), and these individuals were then selected for further examination. A control group comprising 100 age- and gender-matched individuals with normal glucose tolerance and CRP less than 5 was retrospectively generated from the same cohort. RESULTS: One hundred and seventy-six people were diagnosed with impaired glucose tolerance or diabetes mellitus type 2 (IGT/T2DM), and 17 (10%) of these patients had elevated ferritin levels according to the MHF definition. In the control group with normal glucose tolerance, 11% also had hyperferritinemia based on the same ferritin cut-off. Multiple regression revealed a significant association between serum ferritin, male sex, 2-hour glucose value after the glucose load and waist circumference among the patients with IGT/T2DM, while there was no association with age or transferrin saturation. CONCLUSIONS: This study demonstrated a prevalence of metabolic hyperferritinemia in one out of ten people with IGT/T2DM; however, a comparable level of serum ferritin was also detected in the matched control group. Only one person in the IGT/T2DM group had ferritin levels higher than 550 mmol/L. Thus, hyperferritinemia is prevalent in this unselected Norwegian cohort. A relationship between s-ferritin and metabolic syndrome parameters was found in patients with IGT/T2DM, but hyperferritinemia is likely not related to iron overload.