Body mass index through life and adult mortality: results from the British 1946 birth cohort
- 1MRC National Survey of Health and Development, MRC Unit for Lifelong Health and Ageing, 33 Bedford Place, London, UK
- 2Laboratory of Epidemiology, Demography, and Biometry National Institute on Aging, National Institutes of Health, Bethesda, MD, USA
Background
Adult body mass index (BMI) has been consistently related to mortality, but little is known about the impact of earlier life BMI on adult mortality.
Objective
Investigate the impact of childhood, adolescent and early adult BMI on premature adult mortality and assess whether any associations are explained by adult BMI.
Design
Cohort study with prospective information on BMI at ages 2, 4, 6, 7, 11, 15, 20, 26 and 36 years, and mortality follow-up from age 26 to 60 years. BMI was standardised at each age, separately for men and women.
Results
Splines were used to model the non-linear associations between BMI and mortality. In both genders, adult BMI from 20 years onwards showed a consistent U-shaped relationship with adult mortality (overall p-value <0.05 for BMI at ages 20, 26 and 36 years). In females, a similar relationship was observed for adolescent BMI at 15 years (p = 0.02); the hazard ratio (HR) comparing females with low BMI (2 standard deviations (SDs) below mean) vs mean BMI was 2.96 (95% CI 1.26 to 6.97). The corresponding HR for females with BMI 2 SDs above the mean was 1.97 (0.95 to 4.10). In males, increased mortality rates were only seen for low adolescent BMI. BMI in childhood was generally not associated with adult mortality. The exception was BMI at age 4 years in females, where a U-shaped relationship was observed (p = 0.02); HR for low BMI (2 SDs below mean) at 4 years vs mean BMI was 2.13 (0.97 to 4.70). The HR for females with BMI 2 SDs above the mean was 1.67 (0.85 to 3.28), and for females with BMI 3 SDs above mean it was 3.08 (1.21 to 7.83). This association was not explained by subsequent BMI change, adult BMI, smoking, childhood social class or adult educational level.
Conclusions
High and low childhood and adolescent BMI are related to adult premature mortality, especially in women. Interventions to reduce under- and overweight in childhood are required to prevent increasing premature adult mortality in more recent cohorts with greater numbers of overweight children.
