Serum Ferritin, Insulin Resistance, and β-cell Dysfunction: A Prospective Study in Normoglycemic Japanese Men

Objectives: The present cohort study investigated the relationship between serum ferritin levels and indices of insulin resistance and β-cell dysfunction in a normoglycemic population without iron overload disorders. Methods: The study participants included 575 normoglycemic Japanese men aged 35-57 years with serum ferritin levels of 400 μg/L or less. Insulin resistance and β-cell dysfunction were estimated at baseline and after 3 years by the homeostasis model assessments of insulin resistance and β-cell function (HOMA-IR and HOMA-β, respectively). To compare the subsequent changes in HOMA-IR and HOMA-β over a 3-year follow-up period among 3 groups based on tertiles of baseline serum ferritin levels (4.9-87.1, 87.2-140.5, and 140.6-396.8 μg/L), the geometric mean HOMA-IR and HOMA-β values at year 3 were calculated for each group using analysis of covariance, incorporating the respective log-transformed parameters at baseline in addition to age, body mass index and major confounding factors. Results: The multivariate-adjusted geometric mean HOMA-IR at year 3 was significantly higher in those in the highest and middle serum ferritin tertiles (1.24 and 1.22, respectively), compared with the lowest tertile (1.07) (p=0.009). When the total study participants were stratified by median body mass index (22.72 kg/m²), similar positive relationships were observed between serum ferritin levels and HOMA-IR for both obese and non-obese participants. However, the adjusted geometric mean HOMA-β at year 3 was similar among the 3 serum ferritin groups. Conclusions: Elevated serum ferritin levels predicted a subsequent increase in HOMA-IR in normoglycemic Japanese men without iron overload disorders.