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

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Abstract
It has been suggested that household crowding may constitute an environmental risk factor for schizophrenia. The present population-based cohort study explores the associations of childhood family size and living conditions to schizophrenia. The cohort comprised people born at Helsinki University Central Hospital from 1924 to 1933, who went to school in the city and were still living in Finland in 1971. Prospectively gathered data from birth and school health records of these 7086 individuals were collected and linked to the Finnish Hospital Discharge Register. Ninety-eight cases of schizophrenia were identified in the cohort. Number of siblings at school start was significantly associated with schizophrenia when adjusted for sex and age of mother. Number of siblings was negatively correlated with body mass index at age 7. Childhood household crowding, defined as number of people per room, and total number of rooms in household were not significantly associated with schizophrenia. Our study indicates that the total number siblings in household during childhood is of greater importance than childhood number of inhabitants 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 possible underlying mechanisms of the associations found include infectious and psychological factors.