Methodological issues for a large-scale intervention trial of lifestyle modification: Interim assessment of the High-Risk and Population Strategy for Occupational Health Promotion (HIPOP-OHP) Study

Objective: To clarify the methodological issues for the High-risk and Population Strategy for Occupational Health Promotion Study (HIPOP-OHP study), which is a 4-year non-randomized control trial, an interim assessment of male participants was performed 3 years after the baseline survey. Methods: We had approximately 2,500 and 4,000 participants in the intervention and control groups, respectively. The population measures and prevalence of risk factors at each year, and between the baseline and 4th examinations were compared between the two groups. The personal trends of returning participants who were in the study at the 1st and 4th examinations were also evaluated. Results: During the 3 years, an increase in serum HDL cholesterol (2.7 mg/dl), and a reduction in the prevalence of hypertriglycemia detected with fasting blood samples (3.6%) and current smokers (5.4%) were observed in the intervention group. The mean HDL cholesterol level was significantly higher in the intervention group than in the control group at the 4th examination, reversed from the baseline survey. The serum non-HDL cholesterol level was significantly increased only in the control group. There was also a significant increase in the prevalence of hypertriglycemia and high plasma glucose detected with fasting blood samples in the control group. The return participation rate after 3 years was 72.2% for the intervention group and 74.9% for the control group. The above-mentioned changes for risk factors were mainly due to returning participants at each examination. Conclusion: These interventional methods may be effective in improving overall cardiovascular risk factors in the population. However, the low return participation rate will dilute the effect of the intervention.