Introduction: Low socioeconomic position (SEP) is a known risk factor for development of obesity in childhood. e level of parental education is commonly used as proxy for SEP, but family disposable income is likely to also be of importance for SEP. e aim of this study was to determine the e ects of family disposable income on BMI and height trajectories from birth up to eight years of age, and the development of obesity at eight years of age.

Methods: Growth data from birth to eight years age were collected for 3030 Swedish children. Register data on family disposable income was re- trieved from Statistics Sweden, and dichotomized for the analysis by the median value for the group. Register-derived information on parental ed- ucation and national background, maternal BMI, age and smoking status were considered as covariates in longitudinal mixed models and regres- sion analyses.

Results: Mean birth weight was lower in families of lower income, 3.51 kg (SD 0.54) vs. 3.60 kg (SD 0.53) for children of higher-income parents, p < 0.0001. By age 5.5 years and 8 years, however, a reversed relation between groups was seen, where the children of lower income families showed signi cantly higher mean BMI. is di erence was no longer sig- ni cant when adjusting for covariates. Considering height, lower income was strongly related to lower height at 5.5 and 8 years, di erences were strengthened a er adjusting for confounders, -0.44 cm (95% CI -0.75,- 0.13) for age 5.5 years and -0.56 cm (95% CI -0.88, -0.23) at 8 years. e OR of obesity at 8 years age was 1.69 (95% CI 1.05–2.7) for the group of low income compared to the group of high income.

Conclusions: Low family disposable income is related to increased risk of childhood obesity at 8 years of age. is could be attributed to a di erent growth pattern compared to children of high income. Our ndings that children of lower family income had lower mean birth weight and dis- played lower height later in childhood suggest that these children might have an unfavourable metabolic pro le and increased risk of developing the metabolic syndrome. © 2016 S. Karger GmbH, Freiburg