Influence of early life factors on social inequalities in psychiatric outcomes among young adult Norwegian men

Background: Social inequalities in health can to a substantial degree be explained by social causation. However, indirect selection by early life factors has been suggested. The main aim of this study was to estimate how much adult social gradients in selected psychiatric outcomes depended on parental and individual characteristics in early life. Methods: The population comprised all males born in Norway 1967-71 (n = 170 678). We compiled data on several social and biological variables from birth onwards from different national registers. Health outcomes were collected from the Cause of Death Register (suicide) and the Labour and Welfare Administration (psychiatric disability, psychiatric sickness absence). Indicator of socio-economic position was education level at the age of 28 years. Men were followed up between 4 and 9 years from the age of 29 years. Results: Crude rates per 100 000 person-years were 21.8 (suicide), 145.7 (disability) and 1164.7 (sickness absence). Social inequalities were strong and consistent for all outcomes. Parental and individual characteristics accounted for a substantial part of the social inequalities in neurosis or personality disorder disability (44.1%) and a moderate role for inequalities in psychiatric sickness absence (25.6%), schizophrenia disability (20.7%) and suicide (17.4%). General ability at the age of 18 years had strongest influence on the social health gradients. Suicide and schizophrenia disability were associated with a combination of high parental and low own education level. Conclusion: This study indicates that indirect selection explains a substantial part of social inequalities in certain psychiatric outcomes and that early life prevention is important to reduce health gradients.