Study: BMI Affects Ischemic, Hemorrhagic Stroke Risk Differently

Increased body mass index (BMI) in women is associated with an increased risk of ischemic stroke but a decreased risk of hemorrhagic stroke, according to a new study.

The researchers recruited 1.3 million previously stroke-free UK women from 1996 to 2001 (mean age, 57 years) and followed them by record linkage for hospital admissions and deaths. They used Cox regression to estimate adjusted relative risks for ischemic and hemorrhagic (intracerebral or subarachnoid hemorrhage) stroke in relation to BMI and conducted a meta-analysis of published findings from prospective studies on these associations.
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During an average follow-up of 11.7 years, they found 20,549 first strokes, of which 9993 were specified as ischemic and 5852 as hemorrhagic. Increased BMI was associated with an increased risk of ischemic stroke (relative risk, 1.21 per 5 kg/m² BMI) but a decreased risk of hemorrhagic stroke (relative risk, 0.89 per 5 kg/m² BMI).

The BMI-associated trends for ischemic and hemorrhagic stroke were significantly different but were not significantly different for intracerebral hemorrhage (n=2790) and subarachnoid hemorrhage (n=3062). Published data from prospective studies showed consistently greater BMI-associated relative risks for ischemic than hemorrhagic stroke with most evidence (prior to this study) coming from Asian populations.

“I think some people may be a little surprised to see that increased adiposity is actually associated with a decreased risk of hemorrhagic stroke because excess weight is known to increase the overall risk of stroke,” said study coauthor Gillian K. Reeves, PhD, from the Nuffield Department of Population Health, University of Oxford, UK. “However, the established relationship between BMI and overall stroke risk is dominated by the association of BMI with the most common type of stroke, ischemic stroke, and few previous prospective studies have had sufficiently large numbers of cases to be able to reliably examine associations separately for ischemic stroke and hemorrhagic stroke.”

The main conclusion from this study is that different stroke types have different risk profiles, she said. “The implications of these findings for patient care are not yet clear, and the benefits of maintaining a healthy weight on overall health are well established. More work is needed to establish exactly what underlies the inverse relationship between adiposity and hemorrhagic stroke risk.”

Reeves is currently looking at how other known risk factors for stroke, such as smoking and alcohol intake, and conditions such as diabetes, may differ in their effects on ischemic and hemorrhagic stroke.

—Mike Bederka

Reference:

Kroll ME, Green J, Beral V, et al; Million Women Study Collaborators. Adiposity and ischemic and hemorrhagic stroke: prospective study in women and meta-analysis [published online Sept. 7, 2016]. Neurology. doi: http://dx.doi.org/10.1212/WNL.0000000000003171.