title: Influence of calendar period on the association between BMI and coronary heart disease: a meta-analysis of 31 cohorts.
abstract: 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).
  
  
  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 = 15 and 10, respectively) compared to studies starting in or before 1985 (n = 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).
  
  
  CONCLUSIONS
  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.
authors: Center for Prevention and Health Services Research, National Institute for Public Health and the Environment, Bilthoven, The Netherlands. ellen.de.hollander@rivm.nl
authors: Ellen L
authors: EL
authors: de Hollander
authors: Rik P
authors: RP
authors: Bogers
authors: Hendriek C
authors: HC
authors: Boshuizen
authors: Annika
authors: A
authors: Rosengren
authors: Martin J
authors: MJ
authors: Shipley
authors: Paul
authors: P
authors: Knekt
authors: Pierre
authors: P
authors: Ducimetière
authors: Alessandro
authors: A
authors: Menotti
authors: Lisette C  P G M
authors: LC
authors: de Groot
authors: Wanda J E
authors: WJ
authors: Bemelmans
mesh_terms: D015992:Body Mass Index; D003327:Coronary Disease / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000150:complications*; D012307:Risk Factors