Background: The few studies that have examined whether head injury is a risk factor for later schizophrenia have had important methodological problems.
Method: We examined the rates of head injury among 8288 persons in the 15 years up to their first admission with schizophrenia and compared them with 82880 age- and gender-matched controls. We used hospitalization for concussion or severe head injury as a definition of head injury. We controlled for any generally altered accident proneness prior to schizophrenia by also comparing the groups with respect to exposition to fractures not involving the skull or spine.
Results: Males with schizophrenia had significantly reduced exposure to concussion (OR = 0.864, p = 0.024), whereas females had significantly increased exposure (OR = 1.322, p = 0.025). No differences were found as regards severe head injury. Males had significantly reduced risk of other fractures (OR = 0.616, p < 0.0001), whereas the risk in females did not differ from controls (OR = 1.154, p = 0.189). After adjusting head injury with the risk for other fractures, both concussion and severe head injury were significantly increased in males (OR = 1.501, p < 0.001 and OR = 1.516. p < 0.001, respectively) but not in females (OR = 1.15, p = 0.413 and OR = 0.819, p = 0.442, respectively).
Conclusion: Our results do not exclude that for males, head injury may contribute to the risk for schizophrenia in a limited number of cases. This relation may also exist for females, but it is paralleled by an increased liability to traumas in general. Premorbid general accident proneness requires consideration when studying this association.