Differences in risk factors for three types of stroke: UK prospective study and meta-analyses

Objective: To compare associations of behavioural and related factors for incident subarachnoid and intracerebral haemorrhage and ischaemic stroke. Methods: 712,433 Million Women Study participants without prior stroke, heart disease or cancer reported behavioural and related factors at baseline (1999-2007) and were followed by record linkage to national hospital admission and death databases. Cox regression yielded adjusted relative risks (RRs) by type of stroke. Heterogeneity was assessed using chi-squared tests. Where appropriate, meta-analyses were done of published prospective studies. Results: After 12.9 (SD 2.6) years follow-up, 8128 women had an incident ischaemic stroke, 2032 intracerebral haemorrhage and 1536 subarachnoid haemorrhage. In women with diabetes, risk of ischaemic stroke was substantially increased (RR=2.01; 95% CI 1.84-2.20), intracerebral haemorrhage slightly increased (RR=1.31; 1.04-1.65) but subarachnoid haemorrhage reduced (RR=0.43; 0.26-0.69) (heterogeneity by stroke type, p<0.0001). Stroke incidence was greater in women who rated their health as poor/fair compared to excellent/good (RR=1.36; 1.30-1.42). Among 565,850 women rating their heath as excellent/good, current smokers were at an increased risk of all three stroke types (although greater for subarachnoid haemorrhage [15+ cigarettes/day vs never smoker, RR=4.75; 4.12-5.47] than for intracerebral haemorrhage [RR=2.30; 1.94-2.72] or ischaemic stroke [RR=2.50; 2.29-2.72]; heterogeneity p<0.0001). Obesity was associated with an increased risk of ischaemic stroke and a decreased risk of haemorrhagic stroke (heterogeneity p<0.0001). Meta-analyses confirmed substantial heterogeneity in these associations across the three types of stroke. Conclusions: Classic risk factors for stroke have considerably different effects on the three main pathological types of stroke.