Aims: Body iron inhibits the metabolism of adiponectin, an insulin sensitizing adipokine. We investigated the relationships of baseline and average of 4-year change in values of serum adiponectin (sA), serum ferritin (sF) and sA/sF ratio on type 2 diabetes (T2D) risk and insulin sensitivity (Matsuda ISI) and secretion (disposition index; DI30). Methods: Prospective analyses were conducted in participants with impaired glucose tolerance of the Finnish Diabetes Prevention Study (n = 516) recruited in 1993–1998. Cox and linear regression analyses were used to investigate the associations of sA, sF and sA/sF ratio, as continuous variables, with incident T2D, Matsuda ISI, and DI30. Results: During the mean follow-up of 8.2 years, 157 incident T2D cases occurred (intervention group, n = 65 and control group, n = 92). In adjusted models, baseline sA and sA/sF ratio were inversely associated with T2D risk (HR = 0.49, 95% CI 0.31–0.76, P = 0.002 and HR = 0.83, 95% CI 0.70–0.99, P = 0.044, respectively). Furthermore, a direct association was observed with Matsuda ISI (β=0.13, 95% CI 0.03–0.22, P = 0.009, for sA and β=0.04, 95% CI 0.01–0.07, P = 0.035, for sA/sF ratio) during the average 4-year follow-up. The changes in sA and sA/sF ratio were also inversely associated with T2D risk (HR = 0.36, 95% CI 0.20–0.63, P < 0.001 and HR = 0.76, 95% CI 0.62–0.92, P = 0.006, respectively), and directly with Matsuda ISI (β=0.27, 95% CI 0.17–0.38, P < 0.001, for sA and β=0.07, 95% CI 0.03–0.11, P < 0.001, for sA/sF ratio). No consistent associations were found with DI30. Conclusions: Baseline levels and changes during the follow-up in sA and sA/sF ratio are related to T2D risk and insulin sensitivity.
