Effect of dietary and antismoking advice on the incidence of myocardial infarction: a 16-year follow-up of the Oslo Diet and Antismoking Study after its close

Abstract

Background and aim: The Oslo Diet and Antismoking Study was a 5-year randomised controlled trial initiated in 1972-1973 and ended in 1977-1978, which showed that dietary change and smoking cessation reduced the incidence of coronary heart disease among high risk middle-aged men. In an extended follow-up we studied the incidence of myocardial infarction (MI) 16 years after the end of the trial in the intervention and control groups.

Methods: The primary endpoint was the first occurrence of non-fatal and fatal MI including sudden death up to December 31 1993. Cases of fatal MI were identified by linkage to Statistics Norway using each subject's individual personal number. Cases of non-fatal MI were extracted from the hospital records. Cox proportional hazards regression models estimated relationships between changes in total cholesterol and triglyceride concentrations and smoking status and the primary endpoints up to 16 years following the end of the trial.

Results: At 5 and 10 years following the end of the trial the incidence of MI among the 604 men in the intervention (I) and 628 in the control (C) group differed significantly (5-year event rate (I/C) =0.059/0.090; P=0.038 and 10-year event rate (I/C) =0.111/0.155; P=0.023), but the difference faded slowly and subsequently (P=0.069 at 16 years). The reduction in MI in the intervention group was primarily explained by the differences in total cholesterol and triglyceride concentrations between the groups.

Conclusion: This extended follow-up of the Oslo Diet and Antismoking Study found a prolonged benefit of the intervention lasting for at least a decade after the close of the trial. This finding is in accordance with statin and other studies showing that the effect of cholesterol lowering may be prolonged after the end of the intervention.