Modifiable lifestyle behaviours account for most cases of subarachnoid haemorrhage: A population-based case-control study in Australasia

Background: Smoking, hypertension and alcohol excess are the major causal risk factors for subarachnoid haemorrhage (SAH) that are modifiable. We aimed to explore the hypothesis that other modifiable lifestyle factors, such as diet, may also underpin a substantial proportion of the population attributable risk (PAR) of SAH. Methods: In a multi-centre, population-based, case-control study, information on smoking status, history of hypertension, physical activity, dietary intake, alcohol consumption, body mass index, and family history of SAH, were obtained from 432 incident SAH cases and 473 frequency-matched community-based SAH-free controls without SAH. Multivariate analysis was used to identify significant risk factors and associated PARs for SAH, reported with 95% confidence intervals (CI). Results: Smoking and history of hypertension accounted for 30% (95%CI 23-37%) and 21% (10-30%) of SAH, respectively. Additionally, 25% (11-37%) of SAH was attributed to drinking skim or reduced fat milk, 15% (5-24%) to eating fruit less than once weekly, and 13% (5-21%) to eating either the fat on meat or skin on chicken > 4 times weekly. Alcohol excess was not associated with SAH. Conclusions: Smoking cessation and blood pressure control are the most important strategies to prevent SAH. However, drinking skimmed/reduced fat milk, eating fruits regularly, and removing the fat from meats and skin from chicken before consumption may also reduce the burden of SAH.