Among the 31 188 adoptees, 371 had been diagnosed with a non-affective psychosis during follow up. Of these, 131 had been diagnosed with schizophrenia. The basic assumption that there was no association between the age of the biological father and the adoptive father was tested on the 24% of the sample (7588 Swedish-born adoptees) for whom we had information about both biological and adoptive paternal age. There was no association (χ2
We did not observe any increased risk of schizophrenia or non-affective psychosis in adopted children in relation to advancing adoptive paternal age (). On the contrary, there was a seemingly lowered risk for non-affective psychosis in adoptees whose adoptive fathers were aged 35–39 years at birth of the child compared to those whose fathers were 30–34 years (OR: 0.7, 95%CI: 0.6–1.0). Gender, place of birth and socioeconomic group correlated with both exposure and outcome and consequently adjustments were performed for these possible confounders one at a time and all together in a final model (). This did not alter the results.
Odds ratios for schizophrenia and all non-affective psychosis in adopted children in relation to the adoptive paternal age.
The median paternal age of the biological fathers was much lower compared to that of the adoptive fathers among the 7 588 adoptees with known biological and adoptive fathers (26.0 and 35.2 years respectively). In this group of adoptees, 129 had been diagnosed with non-affective psychosis. As in the whole study population there was no increased risk of non-affective psychosis related to advancing adoptive paternal age compared to unexposed (OR: 1.0, 95%CI: 0.6–1.4). As expected, there was an increased risk related to advancing biological paternal age (OR: 1.4, 95%CI: 0.8–2.5), although not statistically significant. The risk did not increase when advancing adoptive and biological paternal age were combined (OR: 1.3, 95%CI: 0.7–2.3).