An individual’s rearing environment contributes, in a meaningful fashion, to his or her risk for major depression, according to study results published in The American Journal of Psychiatry.

The investigators sought to elucidate the role played by rearing environment in the etiology of major depression.

A natural experiment was conducted using data from a Swedish National Sample, in which high-risk full- and half-sibling pairs were exposed to different rearing environments—that is, home-reared vs adopted-away settings. The database for the analysis was created by entering all full- and half-sibling sets in which 1 sibling in the set was adopted away, the other(s) was reared by their common biological parent(s), and at least 1 of the biological parents had a registration for major depression in his or her lifetime. In addition to the primary comparison in the study—that is, the risk for major depression between the home-reared and the adopted-away offspring—the study was also designed to address: “If the reduced risk for major depression in the siblings reared in the adoptive compared with the home environment results from the quality of the rearing environment in the adoptive home, then those differences in risk should decline when the environment is adversely affected by environmental exposures known to increase risk for subsequent depression.”

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High risk for depression was defined as having at least 1 biological parent with major depression. The full-sibling database included a total of 666 adopted individuals who had 1254 full siblings who were raised by the biological parent(s). The half-sibling database included a total of 2596 adopted individuals who had 5511 half siblings who were raised by the biological parent(s). Overall, 267 adoptees were included in both the full-sibling and the half-sibling analyses.  Follow-up time was measured from when the child was 15 years of age until the time of first registration for major depression, death, emigration, or conclusion of follow-up, whichever occurred first. At the end of follow-up, the offspring varied between 15 and 60 years of age.

After controlling for sex, parental age at birth, and history of major depression (for half siblings) in the nonshared parent, the risk for major depression in the matched adopted vs the home-reared full and half siblings was decreased by 23% (95% CI, 7% to 36%) and by 19% (95% CI, 10% to 38%), respectively. The educational status of the biological and adoptive parents did not influence this protective rearing effect. In both full and half sibships, however, the protective effect afforded by adoption disappeared when either an adoptive parent or a stepsibling had major depression, or when the adoptive home was disrupted by parental divorce or death.

The investigators concluded that in matched full and half siblings who are at high risk for major depression, individuals reared in adopted homes—which in Sweden are selected because of their high-quality rearing environment—have a significantly lower risk for major depression compared with individuals reared in their home environment. These findings further enhance the evidence that high-quality rearing environments can meaningfully reduce rates of major depression among individuals at high familial risk.


Kendler KS, Ohlsson H, Sundquist J, Sundquist K. The rearing environment and risk for major depression: a Swedish national high-risk home-reared and adopted-away co-sibling control studyAm J Psychiatry. 2020;177(5):447-453.