Background: The epidemic of childhood obesity is of increasing public health concern, with major implications for long-term health. Prevention strategies are urgently needed. Most of the evidence concerning risk factors for childhood obesity comes from observational studies, mainly from Western populations. In the West, socio-economic position (SEP) is often associated with potential risk factors and with childhood obesity, making these observational studies open to residual confounding. Evidence from a setting with a different confounding structure can be valuable in disentangling whether associations observed in Western settings reflect potentially reversible causal effects of risk factor or are confounded by SEP. Objectives: This thesis took advantage of a large (n=8327), population-representative Chinese birth cohort from a developed non-Western setting, Hong Kong, where the confounding structure between potential risk factors and childhood obesity is different, to examine the association of four modifiable risk factors (mode of delivery, the timing of solid food introduction, type of child care and dairy product consumption) with adiposity from infancy to early puberty. Methods: Adiposity from infancy to early puberty was proxied by age- and sex-specific body mass index (BMI) standardized scores (z-scores) from 3 months to 13 years, relative to the 2006 World Health Organization (WHO) child growth standards for 0-5 years and the 2007 WHO growth reference for 5-19 years. Overweight (including obesity) was defined according to International Obesity Task Force cut-off. I compared three marginal models (maximum likelihood estimation, generalized estimating equations and quantile regression) to ascertain the optimal way of modeling the population-averaged association of early life risk factors with BMI z-score because of the complex data structure with inevitably some missing data. All three methods were used to examine the adjusted associations of mode of delivery and the timing of solid food introduction with BMI z-score from infancy to early puberty and with overweight (including obesity) from early childhood to early puberty. Multivariable linear and logistic regression were used to examine the adjusted associations of the type of child care at 6 months, 3 years, 5 years and 11 years with BMI z-score and overweight (including obesity) at 13 years, and the association of dairy product consumption at 11 years with BMI z-score at 13 years. Results: My analyses were robust to the choice of marginal model. Mode of delivery, the timing of solid food introduction and dairy product consumption were not associated BMI z-score or overweight (including obesity), but informal child care was associated with higher BMI z-score and overweight at early puberty. Conclusions: In this population-representative birth cohort from an understudied non- Western developed setting with little patterning of childhood adiposity by SEP, informal child care (by family members and/or in-home employed help) may be a target for intervention. Conversely, cesarean section, early introduction of solid food and lack of dairy product consumption do not appear to be contributing to the current obesity epidemic. Non-replication in a different context suggests some observed associations in the West may be indicators of residual confounding rather than of causality. / published_or_final_version / Public Health / Doctoral / Doctor of Philosophy

published_or_final_version / Community Medicine / Master / Master of Public Health