Longitudinal pathways between childhood BMI, body dissatisfaction, and adolescent depression: an observational study using the UK Millenium Cohort Study

Background: Globally, more adolescents are having depressive symptoms than in the past. High BMI is a risk factor for depressive symptoms, potentially acting via increased body dissatisfaction. Robust longitudinal evidence of these associations could help to inform preventive interventions, but such evidence remains scarce. We investigated the longitudinal associations between BMI at age 7 years and depressive symptoms at age 14 years (objective 1), BMI at age 7 years and body dissatisfaction at age 11 years (objective 2), and body dissatisfaction at age 11 years and depression at age 14 years (objective 3). We also investigated the extent to which body dissatisfaction mediated the association between BMI and depressive symptoms (objective 4). // Methods: This study used data from the Millennium Cohort Study, a representative longitudinal general population cohort of UK children born between Sept 1, 2000, and Jan 11, 2002. We used univariable and multivariable linear regression models to investigate the associations in objectives 1–3 adjusting for a range of child-level and family-level confounders. For mediation analyses we used non-parametric g-formula (objective 4). We reported stratified results in presence of sex differences. All analyses were based on participants with complete BMI data and imputed confounders and outcomes. // Findings: Our sample included 13 135 participants. Of these, 6624 (50·4%) were male participants and 6511 (49·6%) were female participants; 11 096 (84·4%) were of White ethnicity and 2039 (15·6%) were from a minority ethnic background. At baseline, mean age was 7·2 years (SD 0·25, range 6·3–8·3). In multivariable models, an SD increase in BMI at age 7 years was associated with greater depressive symptoms at age 14 years (estimated regression coefficient [coeff]: 0·30, 95% CI 0·17–0·43) and greater body dissatisfaction at age 11 years (coeff 0·15, 0·12–0·18). Greater body dissatisfaction at age 11 years was associated with higher depressive symptoms at age 14 years (coeff 0·60, 0·52–0·68). All these associations were twice as large in girls as in boys. Body dissatisfaction explained 43% of the association between BMI and depression in girls. // Interpretation: Our findings bear relevance for interventions aimed at reducing weight in childhood and reducing body dissatisfaction. Implementation of evidence-based body image interventions and identification of drivers of weight stigma should be key public health priorities. Interventions aiming to reduce weight in childhood need to avoid increasing body dissatisfaction and should target environmental drivers of weight rather than individuals. // Funding: Wellcome Trust; The Royal Society; Economic and Social Research Council; and the National Institute for Health and Care Research