Breastfeeding is known to benefit both the mother's and the child's health. Our aim was to test the interactive effects between estrogen receptor 1 (ESR1) rs2234693 and breastfeeding when predicting the child's later depression in adulthood. A sample of 1209 boys and girls from the Young Finns Study were followed from childhood over 27 years up to age 30–45 years. Adulthood depressive symptoms were self-reported by the participants using the Beck Depression Inventory. Breastfeeding as well as

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... veral possibly confounding factors was reported by the parents in childhood or adolescence. Breastfeeding tended to predict lower adult depression, while ESR1 rs2234693 was not associated with depression. A significant interaction between breastfeeding and ESR1 was found to predict participants' depression (P=.004) so that C/C genotype carriers who had not been breastfed had higher risk of depression than T-allele carriers (40.5% versus 13.0%) while there were no genotypic differences among those who had been breastfed. In sex-specific analysis, this interaction was evident only among women. We conclude that child's genes and maternal behavior may interact in the development of child's adult depression so that breastfeeding may buffer the inherited depression risk possibly associated with the C/C genotype of the ESR1 gene.