Physical activity and subarachnoid haemorrhage: a population based case-control study.

OBJECTIVE To evaluate physical activity as a risk factor for subarachnoid haemorrhage. METHODS A population based case-control study in King County, Washington. A standardised, personal interview was used to determine physical activity during the past year and at the onset of the bleed for case patients and a similar reference time for control subjects. Conditional logistic regression and a case cross over analysis were performed in which each case patient served as his or her own control. Subjects were 149 men and women with incident, spontaneous subarachnoid haemorrhage and two control subjects per case patient. Control subjects were identified through random digit dialing and matched on age, sex, and respondent type. RESULTS Four of the 149 (2.7%) case patients were engaged in vigorous physical activity at the time of their subarachnoid haemorrhage. With those who were engaged in non-vigorous or no physical activity serving as the reference group, the relative risk of sustaining a subarachnoid haemorrhage for those engaged in vigorous physical activity was 11.6 (95% confidence interval (95% CI) 1.2-113.2). In the case cross over analysis, the relative risk was 15.0 (95% CI 4.3-52.2). Higher levels of long term regular physical activity over the past year were associated with a lower, but not statistically significant, risk of subarachnoid haemorrhage (test for trend, p=0.3). CONCLUSION The risk of subarachnoid haemorrhage is increased during vigorous physical activity, although only a few result from this mechanism.