Associations between childhood living circumstances and schizophrenia: a population-based cohort study

Objective: It has been suggested that household crowding may constitute an enviromental risk factor for schizophrenia. The present population-based co hort study explores the associations of childhood family size and living co nditions to schizophrenia. Method: The cohort comprised people born at Helsinki University Central Hos pital from 1924 to 1933, who went to school in the city and were still livi ng in Finland in 1971. Prospectively gathered data from birth and school he alth records of these 7086 individuals were collected and linked to the Fin nish Hospital Discharge Register. Results: Ninety-eight cases of schizophrenia were identified in the cohort. Number of siblings at school start was significantly associated with schiz ophrenia when adjusted for sex and age of mother. Number of siblings was ne gatively correlated with body mass index at age 7. Childhood household crow ding, defined as number of people per room, and total number of rooms in ho usehold were not significantly associated with schizophrenia. Conclusion: Our study indicates that the total number siblings in household during childhood is of greater importance than childhood number of inhabit ants per room. Subjects who originated from families with many children had been leaner, which may imply that childhood nutritional factors partly is the mediating factor between number of siblings and schizophrenia. Other po ssible underlying mechanisms of the associations found include infectious a nd psychological factors.