Household crowding in early adulthood and schizophrenia are unrelated in Denmark: a nested case-control study.

A number of studies have found that being born in an urban area is a risk factor for developing schizophrenia. It has been hypothesized that increased exposure to infectious agents through household crowding might account for this association. Using Danish longitudinal registers, we have established a population-based sample of 191 cases of schizophrenia where the first admission occurred between 1981 and 1993. These cases were compared with 17413 individually matched controls of the same gender and age. Information regarding parents' and siblings' psychiatric history, urbanization, season and place of birth, and square meter per dweller were included in a conditional logistic regression model. We found square meter per dweller to be insignificant and without any trend when included as a risk factor for schizophrenia, whereas previous findings of schizophrenia associated with being born in an urban area and with schizophrenia in parents and siblings were replicated.