Breast feeding and early adolescent behaviour, self-esteem and depression: Hong Kong's 'Children of 1997' birth cohort.

Objective: Breast feeding may contribute to neurological development and hence mental health. However, associations from Western populations are unclear, and most likely confounded by socioeconomic position (SEP), making evidence from other sociocultural settings valuable. We examined whether breast feeding was associated with early adolescent emotional and behavioural problems, self-esteem and depressive symptoms in a non-Western developed setting, where socioeconomic patterning of breast feeding differs from but other postnatal characteristics are similar to Western settings.

Design: The adjusted associations of breast feeding with emotional and behavioural problems assessed from parent-reported Rutter z-score at ~11 years (n=5598, 67% follow-up), self-reported self-esteem z-score at ~11 years (n=6937, 84%) and depressive symptoms assessed from self-reported Patient Health Questionnaire-9 z-score at ~13 years (n=5797, 70%) were examined using multivariable linear regression in a population-representative Hong Kong Chinese birth cohort, 'Children of 1997'.

Results: Mothers from families with higher education tended to start but not sustain breast feeding, whereas migrant mothers tended to start and sustain breast feeding. Breast feeding for 3+ months had mostly null associations with Rutter score, self-esteem or depressive symptoms adjusted for sex, age, survey mode, SEP, parents' age, birth weight-for-gestational age, birth order and secondhand smoke exposure, although partial breast feeding for any length of time or exclusive breast feeding for <3 months was associated with poorer behaviour (higher Rutter z-score (0.10, 95% CI 0.05 to 0.16)) and lower self-esteem (-0.09, 95% CI -0.14 to -0.04).

Conclusions: In a non-Western developed setting, breast feeding was inconsistently associated with several early adolescent mental health measures suggesting a reflection of setting specific unmeasured confounding.