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

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

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)

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)

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

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

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

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

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

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

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

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

Thank you!