The Helsinki Heart Study: basic design and randomization procedure.

The Helsinki Heart Study is a coronary primary prevention trial in a group of middle aged men with lipid abnormalities. Its aim is to investigate the effects on the incidence of coronary heart disease of simultaneously lowering serum total and low density lipoprotein (LDL)-cholesterol and elevating high density lipoprotein (HDL)-cholesterol with gemfibrozil, over a period of 5 years. Participants were selected from a population of 23 531 men between 40 and 55 years of age. The mean serum total cholesterol among 18 966 screened subjects was 6.3 mmol l-1 (245 mg dl-1) and the mean HDL-cholesterol 1.3 mmol l-1 (50.3 mg dl-1). All subjects meeting the lipid acceptance criterion of non-HDL-cholesterol (i.e. total cholesterol minus HDL-cholesterol) greater than 5.2 mmol l-1 (200 mg dl-1) on two separate occasions two to three months apart, who were free from coronary heart disease or other major illness, were invited to participate. The total cholesterol level for the final 4081 study participants was 7.5 mmol l-1 (290 mg dl-1) and HDL-cholesterol was 1.23 mmol l-1 (47.6 mg dl-1). Mean systolic and diastolic blood pressures were 141.7 and 91.3 mmHg. About 15% of participants were hypertensive and 36% were smokers. A total of 2051 men were randomly allocated to receive gemfibrozil 600 mg twice daily and 2030 matching placebo capsules. A cholesterol-lowering diet was also prescribed for all participants. The randomized treatment groups were well balanced. Equal distribution of major risk factors was achieved in relevant sub-groups. This report describes the procedures involved in setting up the study, summarizes the baseline data obtained and reviews the success of the randomization procedure. Finally, it compares the design of this study with that of some other major preventive trials.