Head injury and Parkinson's disease: a population-based study.

Background: The epidemiological evidence on head injury and the risk of Parkinson's disease (PD) has been inconsistent.

Methods: We examined the relation between previous hospitalization for head injury and PD using a population-based nested case-control design based on the Swedish National Patient Register from 2001 until 2007, including 18,648 PD cases and 93,240 controls, randomly selected from the general population. Exposure was defined as hospitalization for head injury between 1987 and index date.

Results: Overall, previous hospitalization resulting from head injury was associated with an increased risk of PD; this association appeared to be largely explained by head injuries experienced recently, especially within 1 year before PD ascertainment.

Conclusions: Our results do not provide convincing evidence for a causal relationship between head injury later in life and PD.