Abstract P104: Trends in Population Attributable Fractions of Major Risk Factors for Cardiovascular Disease in Japan, 1975 to 2014: The Circulatory Risk in Communities Study
Authors: Takada Midori , Kubota Yasuhiko , Tezuka Kazuhide , Umesawa Mitsumasa , Shimizu Yuji , Yamagishi Kazumasa , Imano Hironori , Sankai Tomoko , Okada Takeo , Kiyama Masahiko , Iso Hiroyasu 
Published: March 2020

Introduction:
Over the past several decades, Asian countries including Japan have experienced westernization of their lifestyles, leading to changes in prevalence of major risk factors for cardiovascular disease (CVD). The estimation of changed in trends of population attributable fraction (PAF) of major CVD risk factors would be useful for planning of CVD prevention strategies.

Hypothesis:
We assessed the hypothesis that PAFs of major CVD risk factors have changed among a Japanese population over the past several decades.

Methods:
We conducted four 10-year cohorts from 1975 to 2014: the baseline of the first cohort as 1975-1977 (n=4,415), that of the second as 1985-1986 (n=7,155), that of the third as 1995-1997 (n=6,892), and that of the fourth as 2005-2007 (n=5,067), consisting of Japanese men and women aged 40-79 years, initially free of CVD, and with valid information on major CVD risk factors (hypertension, diabetes mellitus, hypercholesterolemia, obesity, smoking, alcohol drinking, and atrial fibrilization). Hazard ratios (HRs) and 95 % confidence intervals (95 % CIs) of CVD (incident stroke and ischemic heart disease) risk factors were calculated by Cox proportional hazard model and their PAFs (95 %CIs) were estimated.

Results:
During the median follow-up of 8.1 years, we documented 227 incident CVDs in the first, 251 in the second, 223 in the third, and 132 in the fourth cohort. The age-adjusted incidence rates per 1,000 person-years of CVD decreased over time; 6.4 in the first, 4.3 in the second, 3.4 in the third, 2.3 in the fourth cohort. Through the four cohorts, hypertension was the leading attributable risk factor for CVD, but its contributions decreased from the first to the fourth cohorts: PAF (95% CI)= 51 (33-64)% in the first; 42 (29-53)% in the second; 47 (32-58)% in the third; and 27 (4-45)% in the fourth cohorts. In contrast, the contributions of diabetes mellitus increased between the third and the fourth cohorts and then diabetes mellitus was promoted to the second leading risk factor: PAF (95% CI)= 1 (-4-6)% in the first; 3 (-1-8)% in the second; 3 (-1-7)% in the third; and 17 (8-25)% in the fourth cohorts. The contributions of hypercholesterolemia and other risk factors were small and did not change over time materially. Similar trends were observed for stroke and coronary heart disease.

Conclusions:
The contribution of hypertension for CVD risk decreased, while that of diabetes mellitus increased among Japanese over the past 40 years. Taken together with the steep decrease in stroke incidence, decrease in hypertension has contributed to reducing PAF of hypertension, and also resulted in increase in PAF of diabetes. Although hypertension is still the leading attributable risk factor for CVD, diabetes could be another target of CVD prevention strategy among Japanese.