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Harmonising measures of body size Rebecca Hardy MRC Unit for Lifelong Health and Ageing at UCL

This study discusses the harmonisation process of body size measures across different cohorts, including BMI calculations, childhood and adulthood BMI centiles, and trajectories of overweight/obesity probabilities. The findings highlight shifts in BMI distribution and obesity prevalence over time, influenced by environmental factors and socioeconomic status. Cross-cohort comparisons provide insights into long-term trends, emphasizing the importance of data harmonisation for accurate research conclusions and sensitivity analyses.

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Harmonising measures of body size Rebecca Hardy MRC Unit for Lifelong Health and Ageing at UCL

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  1. Harmonising measures of body size Rebecca Hardy MRC Unit for Lifelong Health and Ageing at UCL William Johnson, Loughborough University David Bann, UCL Institute of Education Leah Li, UCL Institute of Child Health Diana Kuh, MRC LHA at UCL

  2. Studies 0 1 3 5 7 0 7 8 9 10 11 12 13 15 18 0 5 10 16 26 30 34 0 7 11 16 23 33 42 44 50 0 2 4 6 7 11 15 20 26 36 43 53 60-64

  3. Harmonisation process - variables • Document measurement protocols • Weights and heights converted to kg and m • Missing adult heights imputed from previous measures • Decimal age at assessment variables created (consistent assumptions made about missing dates) • Exclude measurements while a woman was pregnant • Standardised data cleaning protocol applied: • removal of biologically implausible values • identification of implausibly large changes (>5 SDs from sex and study stratified mean)

  4. Harmonisation process – study samples • MRC NSHD is representative of singletons born in England, Scotland and Wales in 1946 • Inclusion criteria • Core sample • European/Caucasian/White ethnicity • Singleton births • Survival until 9 months (MCS), 1 year (NSHD, NCDS, ALSPAC), 5 years (BCS70)

  5. Body mass index (BMI) calculated as weight(kg)/height(m)2 • Overweight/obese defined by IOTF age- and sex- specific cut-offs and compared with normal weight

  6. The 98th, 91st, and 50th childhood BMI centiles from sex and study stratified LMS models plotted against the IOTF cut-offs Johnson Plos Med 2015

  7. The 98th, 91st, and 50th adulthood BMI centiles from sex and study stratified LMS models plotted against the normal cut-offs Johnson Plos Med 2015

  8. Trajectories of the probability of overweight or obesity (versus normal weight) from sex and study stratified mixed effects logistic regression models Johnson Plos Med 2015

  9. Conclusions • Shifts have occurred at the upper end of the BMI distribution • three-fold increase in overweight or obesity prevalence in childhood • the age at which median adult becomes overweight or obese has decreased • Impact of the onset of a more obesogenic environment • Recently born cohorts are therefore: • Accumulating greater lifetime exposure to overweight or obesity

  10. Childhood SEP and adult BMI – women 1970 1958 1946 V (lowest) I (highest) Bann et al. In preparation

  11. Adult SEP (42/43y) and BMI ≥42y – women 1970 1958 1946 V (lowest) I (highest) Bann et al. In preparation

  12. Final comments • Cross-cohort comparisons of trajectories provide a powerful approach to study change over time • Data Harmonisation: • Time consuming • Documentation • Harmonisation required within cohorts and between cohorts • Degree of harmonisation dependent on the research questions • Sensitivity analyses

  13. Thank you!

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