Serum ferritin and glucose homeostasis: change in the association by glycaemic state.

ABSTRACT

BACKGROUND: Data on the association between body iron and glucose homeostasis by the three glycaemic states are scarce. Thus, we investigated the association between body iron as assessed by a serum ferritin concentration and glucose homeostasis using homeostasis model assessment (HOMA) of insulin resistance (HOMA-IR) and beta cell function (HOMA-BcF) in different glycaemic states. METHODS: A cross-sectional analysis was conducted in 2541 men aged 42-60 years in 1984-1989 in the Kuopio Ischemic Heart Disease Risk Factor Study. Subjects were classified into the three glycaemic states, normoglycaemia, prediabetes and type 2 diabetes (T2D), by fasting plasma glucose measurements and the information collected at study visit. The association between serum ferritin quartiles and HOMA-IR and HOMA-BcF for each glycaemic state was examined by analysis of covariance and linear regression analysis. RESULTS: The mean age and serum ferritin concentrations were 53.1 years (standard deviation = 5.7, range = 42.0-61.3 years) and 166.2 µg/L (standard deviation = 141.7, range = 11-960 µg/L), respectively. After multivariable adjustments, a weak and direct association was observed between serum ferritin quartiles and HOMA-IR in normoglycaemia (P-trend = 0.001) but a direct association in prediabetes (P-trend = 0.007) and in T2D (P-trend = 0.078). In HOMA-BcF, the association was weak and direct in normoglycaemia (P-trend = 0.003), direct in prediabetes (P-trend = 0.005) and inverse in T2D (P-trend = 0.105). Strongest associations were observed in prediabetes (ß = 0.25, 95% confidence interval = 0.14-0.36 and P = 0.004 in HOMA-IR; ß = 0.23, 95% confidence interval = 0.15-0.31 and P = 0.008 in HOMA-BcF) after a 100-µg/L increase in serum ferritin (log-transformed). CONCLUSIONS: These data suggest that both the strength and the direction of the association between body iron stores and glucose homeostasis are dependent on the glycaemic state of the population.