1 Department of Health, Medicine and Care, General Practice, Linköping University, SE-58183, Linköping, Sweden. par.andersson.white@liu.se.
2 Crown Princess Victoria Children´s Hospital, Region Östergötland, SE-58185, Linköping, Sweden. par.andersson.white@liu.se.
3 PERFORM Centre, Concordia University, H4B 1R6, Montreal, QC, Canada.
4 Centre de recherche du Centre Hospitalier de l'Université de Montréal, H2X 0A9, Montréal, QC, Canada.
5 École de santé publique, Université de Montréal, H2X 0A9, Montréal, QC, Canada.
6 Division of Health Sciences, Warwick Medical School, University of Warwick, CV4 7AL, Coventry, UK.
7 Murdoch Children's Research Institute, Melbourne, VIC, 3052, Australia.
8 Department of Paediatrics, The University of Melbourne, Melbourne, VIC, 3052, Australia.
9 Cree Board of Health and Social Services of James Bay, Department of Program Development and Support, G0W 1C0, Chisasibi, QC, Canada.
10 The Generation R Study Group, Erasmus University Medical Center, 3000 CA, Rotterdam, the Netherlands.
11 Department of Public Health, Erasmus University Medical Center, 3000 CA, Rotterdam, the Netherlands.
12 Stanford University, 94305, Stanford, CA, USA.
13 Department of Pediatrics, Erasmus University Medical Center, 3000 CA, Rotterdam, the Netherlands.
14 Department of Epidemiology, Erasmus University Medical Center, 3000 CA, Rotterdam, the Netherlands.
15 Crown Princess Victoria Children´s Hospital, Region Östergötland, SE-58185, Linköping, Sweden.
16 Division of Pediatrics, Dept of Biomedical and Clinical Sciences, Linköping University, SE-58185, Linköping, Sweden.
17 Department of Health, Medicine and Care, General Practice, Linköping University, SE-58183, Linköping, Sweden.

Background/objectives: This study analysed the relationship between early childhood socioeconomic status (SES) measured by maternal education and household income and the subsequent development of childhood overweight and obesity.

Subjects/methods: Data from seven population-representative prospective child cohorts in six high-income countries: United Kingdom, Australia, the Netherlands, Canada (one national cohort and one from the province of Quebec), USA, Sweden. Children were included at birth or within the first 2 years of life. Pooled estimates relate to a total of N = 26,565 included children. Overweight and obesity were defined using International Obesity Task Force (IOTF) cut-offs and measured in late childhood (8-11 years). Risk ratios (RRs) and pooled risk estimates were adjusted for potential confounders (maternal age, ethnicity, child sex). Slope Indexes of Inequality (SII) were estimated to quantify absolute inequality for maternal education and household income.

Results: Prevalence ranged from 15.0% overweight and 2.4% obese in the Swedish cohort to 37.6% overweight and 15.8% obese in the US cohort. Overall, across cohorts, social gradients were observed for risk of obesity for both low maternal education (pooled RR: 2.99, 95% CI: 2.07, 4.31) and low household income (pooled RR: 2.69, 95% CI: 1.68, 4.30); between-cohort heterogeneity ranged from negligible to moderate (p: 0.300 to < 0.001). The association between RRs of obesity by income was lowest in Sweden than in other cohorts.

Conclusions: There was a social gradient by maternal education on the risk of childhood obesity in all included cohorts. The SES associations measured by income were more heterogeneous and differed between Sweden versus the other national cohorts; these findings may be attributable to policy differences, including preschool policies, maternity leave, a ban on advertising to children, and universal free school meals.