Are bidirectional associations of obesity and depression already apparent in childhood and adolescence as based on high-quality studies? A systematic review.

Our aim was to evaluate bidirectional associations of obesity and depression in cross-sectional and longitudinal studies with initial assessments in childhood or adolescence. The clarification of these relationships may support the development of innovative interventions, e.g. based on nutrition and mental health. A systematic literature search was conducted in MEDLINE. Main inclusion criteria were (i) assessment of subjects <18 years at baseline, (ii) use of validated psychometric instruments and (iii) elicitation of objectively measured anthropometric data at least at one time point. Twenty-four studies met our inclusion criteria. Out of 19, 14 cross-sectional studies confirmed a significant association of obesity and depression. Three out of eight longitudinal studies reported associations between obesity and subsequent depression in female children and adolescents only, and three out of nine studies obtained evidence in favour of the other direction with two studies revealing significant results only for female and one only for male children and adolescents. Evidence is mixed, and secure conclusions are hampered by the methodological variance of the included studies. Relationships are seemingly more readily detectable in female children adolescents and in the cross-sectional compared with the longitudinal analyses. Possibly, the joint development of obesity and depression in predisposed subjects accounts for the latter discrepancy.