Home environment conditions during childhood and psychosocial outcomes across three generations in Sweden: population...

To examine if early adoption into a family with favourable home environment conditions reduces long term psychosocial risks and provides intergenerational benefits among individuals born to parents with psychiatric or behavioural problems.

Population based adoption-discordant sibling comparison study.

Swedish registers of births between 1950 and 1980, with follow-up to 31 December 2020.

Two samples of sibling pairs from at risk families: 4254 full siblings and 7796 maternal half siblings, who were or were not adopted before age 10 years. Offspring of these siblings (born 1965-2020) were also followed to assess intergenerational spillover effects.

The variable of interest was adoption into non-biological families. Outcomes included psychiatric diagnoses, long term unemployment, receipt of social welfare, highest attained education (and upper secondary education ineligibility for generation 3), criminal convictions, and, among men, non-cognitive skills and general intelligence assessed at military conscription.

Adopted individuals (n=1535) showed a lower risk of psychiatric disorders (29.8% v 36.1% among non‑adopted siblings), criminal convictions (26.1% v 34.0%), and receiving social welfare (37.8% v 48.5%). They also showed higher mean intelligence scores (4.5 v 3.8) and non-cognitive skills scores (4.8 v 3.9) and were more likely to have attended university (26.0% v 15.2%). The offspring of adopted individuals (n=2750), in turn, also displayed modestly higher psychosocial functioning than their cousins (eg, 29.6% v 32.3% with psychiatric disorders), although the associations were weaker and less precisely estimated. This pattern of associations was similar in the maternal half sibling sample.

Early adoption into a family with favourable home environment conditions was associated with moderate, enduring benefits across psychiatric, social, and cognitive outcomes, extending into the next generation. These results highlight the potential for environmental improvements during childhood to mitigate intergenerational disadvantage.