[Trends in cohort effects of cardiovascular disease mortality in Japan, 1950-2010]

The average systolic blood pressure value among Japanese individuals has decreased rapidly from a peak in 1965 to 1990, and cardiovascular disease mortality has correspondingly decreased. The age-adjusted ischemic heart disease mortality rate has also decreased. However, the westernized lifestyle, with its associated effects on development of cardiovascular disease, is increasing rapidly in Japan. Consequently, there are concerns that the current reduction in the cardiovascular disease mortality rate will cease and actually increase in the near future. We used an age-period-cohort (APC) model to decompose cardiovascular disease mortality trends into individual effects of age, period, and cohort to analyze the cohort effects of cardiovascular disease.

We used 5-year interval vital statistical data from 1950-2010 to create 13 classes. Subjects aged 30-89 years were divided into 5-year age groups to create 12 classes. Birth cohorts in this analysis included individuals born from 1861 to 1865, which corresponded to individuals aged, 85 to 89 years in 1950, up to individuals born from 1976 to 1980, who were 30 to 34 years old in 2010. A total of 24 groups were created. We estimated the effect of each characteristic using the sequential method in APC analysis with the assumption that age effects are predominant.

The period effects of cardiovascular disease mortality declined consistently. However, the cohort effects, which declined until the cohort born in 1988, stopped declining or increased slightly in men and women born around 1938 and 1943, respectively.

The results showed a consistent decline in period effects on cardiovascular mortality, which presumably reflect improved living, healthcare, and medical environments. However, analysis of cohort effects did not show a steady decline in younger generations. Decreased average systolic blood pressure among Japanese citizens is associated with reduced risk of cardiovascular disease. If a westernized lifestyle also plays a part in the cohort effects and is associated with the observed slowdown or cessation of reduced systolic blood pressure, it is possible that the number of cardiovascular deaths may increase in younger generations. This possibility needs to be taken into consideration in future implementation of public health activities.