Objective: The association between obesity and coronary heart disease (CHD) may have changed over
time, for example due to improved pharmacological treatment of CHD risk factors. This meta-analysis of
31 prospective cohort studies explores the influence of calendar period on CHD risk associated with
body mass index (BMI).
Design and Methods: The relative risks (RRs) of CHD for a five-BMI-unit increment and BMI categories
were pooled by means of random effects models. Meta-regression analysis was used to examine the
influence of calendar period (>1985 v 1985) in univariate and multivariate analyses (including mean
population age as a covariate). Results: The age, sex, and smoking adjusted RR (95% confidence intervals) of CHD for a five-BMI-unit
increment was 1.28(1.22:1.34). For underweight, overweight and obesity, the RRs (compared to normal
weight) were 1.11(0.91:1.36), 1.31(1.22:1.41), and 1.78(1.55:2.04), respectively. The univariate analysis
indicated 31% (95%CI: 56:0) lower RR of CHD associated with a five-BMI-unit increment and a 51%
(95%CI: 78: 14)) lower RR associated with obesity in studies starting after 1985 (n ¼ 15 and 10,
respectively) compared to studies starting in or before 1985 (n ¼ 16 and 10). However, in the multivariate
analysis, only mean population age was independently associated with the RRs for a five-BMI-unit
increment and obesity ( 29(95%CI: 55: 5)) and 31(95%CI: 66:3), respectively) per 10-year
increment in mean age).
Conclusion: This study provides no consistent evidence for a difference in the association between BMI
and CHD by calendar period. The mean population age seems to be the most important factor that
modifies the association between the risk of CHD and BMI, in which the RR decreases with increasing
age
