Factors affecting glucose tolerance in hereditary hemochromatosis.

OBJECTIVE To determine insulin action and insulin secretory function in patients with hemochromatosis, and to find evidence for or against hypothesized pathogenetic mechanisms for the abnormal glucose metabolism associated with hemochromatosis. These mechanisms include decreased beta-cell secretion of insulin due to iron overload, insulin resistance and genetic factors. DESIGN Prospective in vivo study. PARTICIPANTS Seventeen subjects with hemochromatosis, of whom 4 had cirrhosis but not diabetes mellitus, 6 had diabetes mellitus and 7 had neither; 10 controls. INTERVENTIONS Insulin sensitivity and insulin secretion were determined during an intravenous glucose tolerance test. Insulin secretion was measured as the acute insulin response to glucose (AIRg). Insulin sensitivity (Si) was quantified with the minimal-model method. Of the patients with hemochromatosis, 14 agreed to undergo a second metabolic study after treatment with venous phlebotomy. RESULTS All subjects with hereditary hemochromatosis had impaired glucose tolerance as measured by K(g) (rate of glucose disappearance). Subjects who were free of both diabetes mellitus and liver cirrhosis had a normal S1 and a decreased AIRg. In these subjects, phlebotomy treatment normalized serum ferritin levels, increased AIRg by 35% and normalized glucose tolerance (K(g)). Subjects with hemochromatosis and cirrhosis had a reduced Si and maintained a normal insulin secretion. Phlebotomy treatment did not change these parameters. Subjects with hemochromatosis and diabetes mellitus had both a reduced Si and AIRg, and these parameters were unaffected by phlebotomy treatment. CONCLUSIONS These results suggest that iron overload can impair insulin secretion and glucose tolerance early in hereditary hemochromatosis, before cirrhosis occurs. Phlebotomy treatment can reverse these defects. Impaired glucose tolerance resulting from insulin resistance in subjects with cirrhosis or diabetes mellitus is not affected by phlebotomy treatment.