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:

1.Shorter stature2.Greater adiposity

•Little is known about when the socioeconomic differentials appear

Objectives

• Model trajectories of growth across childhood:

1. Height2. 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?

Methods

Height and weight data in ALSPAC

1. Birth weights/lengths (obstetric records & ALSPAC staff visiting hospitals)

2. Routine child health records(health visitors, up to 4 measures per child)

3. Research clinics (CiF and Focus)

4. Questionnaires (mother-reports, up to 4 per questionnaire)

Data – birth to ten years

Height Weight

Boys N= 7194

Median = 5

IQR = 2-8

N= 7248

Median = 5

IQR = 3-8

Girls N= 6733

Median = 5

IQR = 2-8

N= 6781

Median = 5

IQR = 3-8

Adiposity measures

•Ponderal index (kg/m3) for 0-2 years

•BMI (kg/m2) for 2-10 years

Analysis 1

1. Fractional polynomials to estimate overall shape

2. Identification of rough spline points

3. 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

4060

8010

012

014

0he

ight

(cm

)

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102108114120Age (months)

Height

Spline points

Boys: 3, 10, 29 months

Girls: 2, 11, 32 months

Boys’ mean heights by maternal education

Age (months)Less than O-Level O-Level A-Level

Degree or above

12 76.18 76.41 76.43 76.48

60 108.76 109.36 109.40 109.76

120 140.56 141.40 141.36 141.97

By 10 years: 1.4cm difference between highest and lowest groups

Girls’ mean heights by maternal education

Age (months) Less than O-Level O-Level A-Level Degree or above

12 75.24 75.45 75.31 75.49

60 107.88 108.47 108.50 109.10

120 139.68 140.18 140.69 141.40

By 10 years: 1.7cm difference between highest and lowest groups

Ponderal Index

Spline points

Boys: 2 months

Girls: 1, 4 months18

2022

2426

Pon

dera

l Ind

ex (

kg/m

3)

0 3 6 9 12 15 18 21 24Age (months)

Boys’ ponderal index by maternal education

Age (months) Less than O-Level O-Level A-Level Degree or above

6 25.33 25.49 25.48 25.36

12 23.17 23.29 23.27 23.18

18 21.01 21.10 21.06 21.00

24 18.85 18.91 18.85 18.82

Age (months) Less than O-Level O-Level A-Level Degree or above

6 25.68 25.74 25.73 25.48

12 23.34 23.35 23.42 23.17

18 21.00 20.95 21.12 20.86

24 18.66 18.56 18.82 18.55

Girls’ ponderal index by maternal education

BMI

Spline points

Boys: 56, 67, 73, 79,

105 months

Girls: 60, 65, 75, 81,

103 months

1616

.517

17.5

BM

I (kg

/m2)

24 30 36 42 48 54 60 66 72 78 84 90 96 102 108 114 120Age (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