Relationship of serum C3 to fasting insulin, risk factors and previous ischaemic events in middle-aged men

Aims Serum C3 is a powerful indicator of the risk of myocardial infarction, which correlates with body mass index, serum lipids and blood pressure. Th is study was performed to ascertain whether such correlations may be explai ned by an association of C3 with fasting insulin, and to assess comparative ly the relationships of C3 and traditional risk factors to previous myocard ial infarction. Methods and Results The fasting levels of C3, insulin, and the main risk factors were evaluated in 1090 unselected men aged 55-64 year s, including 129 cases of previous ischaemic events (51 myocardial infarcti ons). In multivariate analysis C3 was associated with insulin (r = 0.27, P < 0.0001), cholesterol (r = 0.18, P < 0.0001), body mass index (r = 0.13, P < 0.0001), glucose (r = 0.12, P = 0.0001), systolic blood pressure (r = 0. 10, P < 0.001), triglycerides (r = 0.09, P < 0.01) and HDL-cholesterol (r = -0.06, P < 0.05). These variables explained 31% of the total C3 variance. Alcohol consumption and physical activity correlated inversely with C3, whi le no correlation was found with smoking and family history of myocardial i nfarction. C3 was associated with previous myocardial infarction and stroke , but not with angina pectoris and peripheral arterial disease. In logistic regression the variables associated with previous myocardial infarction we re C3 (P < 0.011), family history of myocardial infarction (P = 0.018), ex- smoker status (P = 0.020), age (P = 0.025), glucose (P = 0.028) and HDL-cho lesterol (P = 0.051, inverse relationship). Conclusions The association of C3 with myocardial infarction persists retrospectively, and is more signifi cant than any other association of traditional risk factors with previous m yocardial infarction. Of the many variables associated with C3, fasting ins ulin is its main covariate, which suggests that C3 is a marker of a pro-ath erogenic metabolic imbalance partly coinciding with insulin resistance. (C) 2000 The European Society of Cardiology.