Non-communicable Disease Risk Factors Life-course body mass index trajectories and blood pressure in mid life in two British birth cohorts: stronger associations in the later-born generation

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, n1⁄4 4787; 7, 11, 16, 23, 33 and 45 y: 1958 cohort, n1⁄416 820] and midadult BP. We adopted linear spline models with random coefficients to characterize childhood and adult BMI slopes. Results: Mean systolic BP (SBP) decreased from the earlierto 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 laterthan the earlier-born cohort by 1.3-1.8 kg/ m, 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 r1⁄4 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 [r1⁄4 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 laterborn cohort suggests that BMI-related effects may have been offset by improvements in other factors linked to BP, such as diet and smoking.