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Socioeconomic position and trajectories of growth and adiposity across childhood. Laura Howe, Social Medicine, University of Bristol. Inequalities in growth and adiposity. Socioeconomic disadvantage is associated with: Shorter stature Greater adiposity
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Socioeconomic position and trajectories of growth and adiposity across childhood Laura Howe, Social Medicine, University of Bristol
Inequalities in growth and adiposity • Socioeconomic disadvantage is associated with: • Shorter stature • Greater adiposity • Little is known about when the socioeconomic differentials appear
Objectives • Model trajectories of growth across childhood: • Height • Adiposity • Explore how these growth curves differ by socioeconomic position (SEP)
Research questions • Do the overall patterns of growth and adiposity change differ by SEP? • What is the magnitude of socioeconomic differentials at different ages? • Are there gender differences in the patterns of socioeconomic differentials?
Height and weight data in ALSPAC • Birth weights/lengths (obstetric records & ALSPAC staff visiting hospitals) • Routine child health records(health visitors, up to 4 measures per child) • Research clinics (CiF and Focus) • Questionnaires (mother-reports, up to 4 per questionnaire)
Adiposity measures • Ponderal index (kg/m3) for 0-2 years • BMI (kg/m2) for 2-10 years
Analysis 1 • Fractional polynomials to estimate overall shape • Identification of rough spline points • Optimisation of spline points
Analysis 2 • Random effects multi-level models in MLwiN • Individual-level residuals provide an individual’s deviation from the average(intercept and slope for each period) • Interactions with SEP
Results • Overall shapes of curves did not differ by SEP • Spline points were therefore estimated for all SEP groups combined
Height Spline points Boys: 3, 10, 29 months Girls: 2, 11, 32 months
Boys’ mean heights by maternal education By 10 years: 1.4cm difference between highest and lowest groups
Girls’ mean heights by maternal education By 10 years: 1.7cm difference between highest and lowest groups
Ponderal Index Spline points Boys: 2 months Girls: 1, 4 months
BMI Spline points Boys: 56, 67, 73, 79, 105 months Girls: 60, 65, 75, 81, 103 months
Conclusions: Height • Socioeconomic differentials in height are largely established by birth length and growth between 1 and 3 years • Socioeconomic differentials in height are greater for girls than boys • By 6 years-old there is a clear height gradient across all four categories of maternal education for girls. Intermediate education groups remain similar for boys
Implications: Height • Pre-natal and early life factors are the most important determinant of socioeconomic differentials in height
Conclusions: Ponderal Index • There is no clear socioeconomic gradient in ponderal index in the first 2 years of life
Conclusions: BMI • From 4 years onwards, boys whose mothers are educated to degree-level have lower BMI • There is no BMI gradient across other categories of maternal education • From 4 years onwards, girls whose mothers are educated to degree-level have lower BMI • Inequalities are wider in girls, and there is a clearer gradient across all categories of maternal education
Implications: Adiposity • Socioeconomic inequalities in adiposity are established early in childhood • Interventions could be aimed at pre-school and early-school children
Remaining questions • WHY are inequalities wider in girls? • Cohort effects?
Next steps • Variables for ALSPAC archive will be available for all to use • Associations of growth with other childhood outcomes/exposures • Modelling growth later into childhood to include puberty
Acknowledgements • Kate Tilling, Debbie Lawlor, Bruna Galobardes, Paul Clarke, Fiona Steele