title: Life-course body mass index trajectories and blood pressure in mid life in two British birth cohorts: stronger associations in the later-born generation.
abstract: BACKGROUND
  Little is known about the impact of recent increases in obesity and more rapid gains in body mass index (BMI) on cardiovascular risk factors. We investigated life-course BMI trajectories associations with adult blood pressure (BP) across two generations.
  
  
  METHODS
  We used the the 1946 and 1958 British birth cohorts. Joint multivariate response models were fitted to longitudinal BMI measures [7, 11, 16, 20, 26, 36, 43 and 50 y (years): 1946 cohort, n = 4787; 7, 11, 16, 23, 33 and 45 y: 1958 cohort, n = 16,820] and mid-adult BP. We adopted linear spline models with random coefficients to characterize childhood and adult BMI slopes.
  
  
  RESULTS
  Mean systolic BP (SBP) decreased from the earlier- to later-born cohort by 2.8 mmHg in females, not males; mean diastolic BP (DBP) decreased by 3.2-3.3 mmHg (both sexes). Adult BMI was higher in the later- than the earlier-born cohort by 1.3-1.8 kg/m(2), slopes of BMI trajectory were steeper from early adulthood and associations with adult BP were stronger. Associations between adult BMI and SBP were stronger in the later-born cohort. For males, childhood BMI slope was associated with SBP only in the later-born cohort; the association for adult BMI slope was stronger in the later-born cohort: correlation coefficient r = 0.28 [95% confidence interval (CI): 0.25,0.33] versus 0.13 (0.06,0.20). For females, childhood slope was associated with SBP in both cohorts; adult slope was associated with SBP only in the 1958 cohort [r = 0.34 (0.31,0.37)]. Patterns of child-to-adult BMI associations were similar in relation to DBP.
  
  
  CONCLUSIONS
  BP did not increase between two generations born 12 y apart despite higher BMI levels. A stronger association between BMI trajectory and BP in the later-born cohort suggests that BMI-related effects may have been offset by improvements in other factors linked to BP, such as diet and smoking.
authors.affiliation: Centre for Paediatric Epidemiology & Biostatistics and leah.li@ucl.ac.uk.
authors.forename: Leah
authors.initials: L
authors.lastname: Li
authors.affiliation: MRC Unit for Lifelong Health and Ageing, University College London, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Hardy
authors.affiliation: MRC Unit for Lifelong Health and Ageing, University College London, UK.
authors.forename: Diana
authors.initials: D
authors.lastname: Kuh
authors.affiliation: Centre for Paediatric Epidemiology & Biostatistics and.
authors.forename: Chris
authors.initials: C
authors.lastname: Power
mesh_terms: D001794:Blood Pressure / Q000502:physiology*; D001795:Blood Pressure Determination; D015992:Body Mass Index; D015988:Cohort Effect; D015331:Cohort Studies; D003971:Diastole; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009765:Obesity; D012307:Risk Factors; D013599:Systole; D006113:United Kingdom
keywords: BMI trajectories; Cohort study; blood pressure; joint modelling; life course