Aim: This study aimed to investigate whether the impact of body mass index (BMI) on the risk of cardiovascular disease (CVD) has changed among the 1960s, 1970s, 1980s, 1990s, and early 2000s in Japan.
Methods: The study population consisted of residents in Japan aged 40-69 years who had no history of CVD. The baseline surveys have been conducted every year since 1963. We defined the first, second, third, fourth, and fifth cohorts as 1963-1969 (n=4,248), 1970-1979 (n=6,742), 1980-1989 (n=12,789), 1990-1999 (n=12,537), and 2000-2005 (n=9,140) respectively. The participants were followed up for a median of 15 years for each cohort to determine the incidence of CVD. We classified them into four categories (BMI ＜21.0, 21.0-＜23.0, 23.0-＜25.0, and ≥ 25.0 kg/m2).
Results: From 1963-1969 to 2000-2005, the prevalence of BMI ≥ 25.0 increased over time. Compared with BMI 23.0-＜25.0, the age-, sex- and community-adjusted hazard ratios (95% confidence interval [CIs]) of CVD for BMI ≥ 25.0 were 1.10 (0.77-1.57), 0.89 (0.68-1.18), 1.03 (0.85-1.26), 1.28 (1.04-1.58), and 1.36 (1.04-1.78) in the first, second, third, fourth, and fifth cohorts, respectively. The corresponding population attributable fractions were 2.0% (nonsignificant), -2.6% (nonsignificant), 0.9% (nonsignificant), 7.6%, and 10.9%. Further adjustment for systolic blood pressure and antihypertensive medication use in the fourth and fifth cohorts attenuated the associations, which may reflect that blood pressure may mediate the BMI-CVD association.
Conclusion: The proportion of CVD attributable to overweight/obesity has increased during the periods between 1963-1969 and 2000-2005. The significant associations between overweight/obesity and risk of CVD after the 1990s were mediated by blood pressure levels.
Keywords: Body mass index; Cardiovascular disease; Cohort study; Population attributable fraction.