Iron status and coronary heart disease: negative findings from the NHANES I epidemiologic follow-up study.

The potential association between iron status and coronary heart disease has received increased attention recently. The authors examine this hypothesis in the First National Health and Nutrition Examination Survey (NHANES I) Epidemiologic Follow-up Study. The study consisted of 4,237 respondents (1,827 men, 2,410 women) aged 40-74 years at baseline. During the average 13-year follow-up, 489 persons (289 men, 200 women) had an acute myocardial infarction, and 1,151 persons (633 men, 518 women) developed coronary heart disease (included myocardial infarction and other forms of chronic ischemic heart disease). In logistic regression analyses, adjusting for baseline age, systolic blood pressure, serum cholesterol, smoking status, and education, serum iron was inversely associated with the risk of myocardial infarction in women (relative risk = 0.82 for an increase of 5.4 mumol/liter (equivalent to about 1 standard deviation), 95% confidence interval (CI) 0.70-0.95), but not in men. Total iron-binding capacity and transferrin saturation were not related to myocardial infarction in either sex, while serum iron and transferrin saturation were inversely associated with coronary heart disease in both sexes. Among men, the relative risk was 0.92 (95% CI 0.85-1.00) for a 5.4-mumol/liter increase in serum iron, while a relative risk of 0.91 (95% CI 0.83-1.00) was observed for a 10% increase in transferrin saturation. For women, the corresponding relative risks were 0.86 (95% CI 0.77-0.95) and 0.88 (95% CI 0.79-0.98), respectively. Dietary iron intake based on 24-hour recall was not associated with the two disease end points. These findings from a large national sample do not support the hypothesis of a positive iron-coronary heart disease relation.