Oslo Study of Diet and Anti-Smoking Advice

Background/Question:

The Olso Study asked the question: could reduction in risk factors work to reduce risk of CVD in men at high risk but who did not have signs or symptoms of CVD? The study focused on changing life-style variables, diet and smoking habits, to lower serum cholesterol levels, blood pressure, serum triglycerides levels, and body weight.

Population/Methods:

All men between the ages of 40 and 49 in Oslo, Norway, were invited for a coronary risk factor screening. 65% (16,202) responded and came for the screening, from whom 1,232 were chosen as having high risk. The men were randomly assigned into a control group and intervention group.; the latter received a short conversation with a physician about the risk factor concept and the purpose of the study and brief dietary advice from a dietitian and advice about quitting smoking. Wives of the men in the intervention group were also given dietary and smoking advice in group sessions. The intervention group was reexamined every 6 months and the control group every year for 5 years.

The primary endpoint was the first occurrence of non-fatal and fatal MI including sudden death. 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:

In the intervention group, levels of smoking decreased early, but increased slightly in the fourth and fifth years, nevertheless, non-smokers increased from 20% to 45%. The control group saw an increase in the numbers of non-smokers as well, from 20% to 35%. There was a significant early decrease in serum cholesterol levels in the intervention group ranging (10.2 to 14.9%), with a slight rise in the 4th and 5th years. The control group also showed a slight decrease ranging from 1.4 to 4.6% decrease. In serum triglycerides there was a 20% decrease difference in the intervention group in relation to the control group. Uric acid, body weight, and blood pressure also showed larger decreases in the intervention group.

Conclusions/Discussion:

This study was among the first to show that “most non-symptomatic, high risk men can also be persuaded to change their habits to a considerable extent.” Previous studies had showed that in symptomatic individuals. 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 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. 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. (FB/HB)