Background Coronary heart disease (CHD) mortality has declined substantially in Japan for several decades. However, the contributory factors remain unclear because major CHD risk factor levels have paradoxically increased since 1980, notably cholesterol, obesity and diabetes. Our objective is to quantify the contributions of prevention and treatment to the coronary heart disease mortality trends in Japan between 1980 and 2012.

Methods We used the previously validated IMPACT model to analyse mortality trends between 1980 and 2012 in the Japanese population aged 35–84 years. This model integrates data on changes in population size, CHD mortality, risk factors, and uptake of evidence-based cardiac treatments. Main data sources included official vital statistics, national patient, health and nutrition surveys, and the health insurance claims data. Relative risks and regression coefficients came from the published meta-analyses. The difference between observed and expected CHD deaths in 2012 was then partitioned among treatment benefits and risk factor changes. We also performed probabilistic sensitivity analyses to quantify the potential effects of parameter uncertainty.

Results From 1980 to 2012, age-adjusted CHD mortality rates in Japan fell by 61%, resulting in 75,680 fewer CHD deaths in 2012 than if rates had not fallen. Improvements in medical and surgical treatments were associated with approximately 59% (range, 56% to 61%)of the total mortality decrease. Major contributions came from therapy for angina in the community (explaining approximately 17% of the mortality fall), antihypertensive medication (≈10%), and heart failure therapies (≈7%).

Risk factor changes accounted for approximately 31% (19% to 42%) of the mortality fall. Some 24% from decreases in systolic blood pressure and 11% from falls in smoking prevalence. However, rises in cholesterol, BMI and diabetes negated some of these benefits, potentially increasing mortality by 2%, 3% and 6% respectively.

Conclusion Approximately 60% of the CHD mortality fall in Japan between 1980 and 2012 was attributable to increases in evidence-based medical treatments, and 30% to falls in population risk factors. However, the substantial contributions from falls in blood pressure and smoking were offset by adverse trends in cholesterol, obesity and diabetes. Our results highlight the potential for further improvements in cardiovascular risk factors in Japan.