Design and baseline characteristics of a cohort study in Japanese patients with hypercholesterolemia: the Japan lipid intervention trial (J-LIT)

Abstract

Objectives: The Japan Lipid Intervention Trial is a cohort study to (1) ascertain the optimal cholesterol levels to be maintained in preventing coronary heart disease (CHD) and other cardiovascular diseases and (2) assess the effect of simvastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, on the serum lipid profile of Japanese patients with hypercholesterolemia. This report summarizes the study protocol and baseline characteristics of the study patients. Methods: Between November 1992 and June 1993, Japanese patients from all 43 prefectures and 3 specially administered cities were screened based on relative population statistics. Of 54,203 patients screened at 5289 institutions by 6511 investigators, 52,421 patients (96.7%; 17,424 men and 34,997 women) with a serum total cholesterol (TC) level ≥220 mg/dL were enrolled in this study and treated with open-labeled simvastatin 5 to 10 mg/d for 6 years. Patients were assigned as follows: 5127 patients (9.8%; 2194 men and 2933 women) with documented CHD to the secondary prevention cohort; the remaining 47,294 patients (90.2%; 15,230 men and 32,064 women) formed the primary prevention cohort. Results: Baseline lipid levels for the primary and secondary prevention cohorts, respectively, were: TC, 270 ± 34 mg/dL and 265 ± 30 mg/dL; high-density lipoprotein cholesterol (HDL-C), 52.9 ± 15.1 mg/dL and 50.5 ± 15.0 mg/dL; triglycerides (TG), 196 ± 171 mg/dL and 196 ± 144 mg/dL; and low-density lipoprotein cholesterol, 182 ± 34 mg/dL and 179 ± 32 mg/dL. Hypertension (45.0% and 47.0%, respectively) and diabetes mellitus (15.1% and 18.6%, respectively) were prevalent in both cohorts. In addition to hypercholesterolemia, 3 or more risk factors were detected in 12.5% and 32.8% of the primary and secondary prevention cohorts, respectively. In both cohorts serum TC and HDL-C levels were higher in women than in men. In contrast, the serum TG level was higher im men than in women. Serum TC and TG levels were higher in younger patients than in elderly patients. The serum HDL-C level was also higher in younger patients, except in women in the primary prevention cohort. Obesity was more common in patients with low serum HDL-C. Patients with high serum TG levels had a high frequency of hypertension, diabetes mellitus, and obesity. No significant correlation was noted between any of the lipid levels and blood pressure. Conclusions: The male:female and CHD:non-CHD distributions were similar to those found in a cross-sectional survey conducted in Japan, suggesting that the study population provides an appropriate model for investigating hypercholesterolemia in Japanese patients. Final analysis of the results of this study will clarify the relationship between the incidence of CHD and other cardiovascular diseases in Japanese hypercholesterolemic patients and cholesterol levels in a large number of subjects receiving simvastatin. It will also indicate the optimal cholesterol levels to be maintained to prevent CHD and other cardiovascular disease and assess the safety of long-term simvastatin therapy. These results will be reported at the end of 2000.