LOW IRON-BINDING-CAPACITY AS A RISK FACTOR FOR MYOCARDIAL-INFARCTION

Background In a recent Finnish study, ferritin was suggested to be an independent risk factor for acute myocardial infarction. This study su ggested that high levels of iron stores might thus be atherogenic and possibly explain partly the sex difference in the incidence of ischemi c heart disease. Methods and Results A randomly selected group (n=2036 ), men and women aged 25 to 74 years, were examined between June and S eptember 1983. All classic risk factors for coronary artery disease we re measured as well as basic hematologic parameters and the parameters of iron metabolism, ie, iron, total iron-binding capacity (TIBC), and ferritin. During the follow-up for 8.5 years, 81 subjects experienced acute myocardial infarction (63 men and 18 women). The differences in the iron parameters between men and women were almost exclusively see n in ferritin values (198 mu g/L in men and 91 mu g/L in women), where as small differences were seen in TIBC. The Cox proportional hazards m odel was used to estimate the contribution of independent variables to the risk of myocardial infarction. TIBC was found to be a strong inde pendent negative risk factor in men (RR=0.95; 95% CI, 0.92 to 0.98), w hereas ferritin (RR=0.999; 95% CI, 0.997 to 1.001) or other iron param eters had no significant predictive power. Each increase in TIBC of 1 mu mol/L was associated with a 5.1% decrease in the risk of myocardial infarction. The classic major risk factors, ie, blood pressure, smoki ng, total cholesterol, and high-density lipoprotein, had significant i ndependent correlation with myocardial infarction. When Cox multivaria te analysis was carried out on both sexes combined, TIBC was still an independent negative risk factor, and the logarithmic transform of fer ritin had a weak negative correlation but was not statistically signif icant. Sex was in this group still a very strong risk factor after tak ing into account all classic risk factors as well as the parameters of iron metabolism. Conclusions This study suggests that transferrin, me asured as TIBC, is an independent negative risk factor for myocardial infarction. Other parameters of iron metabolism, including ferritin, w ere not found to contribute to the risk.