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
I am sure you are all aware of the studies. We are focusing on the nationally representative studies, with the addition of ALSPAC to fill the 31 year gap between BCS in 1970 and MCS in 2001.
I have produced this figure to show the main ages of data collection in each study. With the exception of age 0 years, weight and height are available at most of these ages.
As CLOSER progresses, I am sure we will add Life Study to this figure.

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
Some sex int sig at 42/43y (58 and70c) , some not (46c)
V (lowest)
I (highest)
Bann et al. In preparation

11. Adult SEP (42/43y) and BMI ≥42y – women
1970
1958
1946
Sex interactions all highly significant for 42/43y in regg
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!