The Risk of Stroke in People with Different Blood Groups

Most people know if they are A, B, AB, or O.  This is important if they have an accident and need a blood transfusion, or if they are blood donors.  But it’s also important, apparently, in assessing your risk of having a stroke.  This is a finding reported by a Harvard School of Public Health scientist at the recent American Heart Association meeting.

Data were obtained from two large studies with 26 and 20 years’ follow-up, respectively.  The Nurses’ Health Study (NHS) included more than 62,000 women, and the Health Professionals Follow-up Study included 27,800 men.  The information on blood groups was self-reported, but this has been shown before to be very accurate.  The data were adjusted for age, smoking, body mass index (BMI), alcohol use, physical activity, aspirin use, race, family health history, and hormone use.  At baseline, the average age was 46 for women and 53 for men.   

Compared to blood type O, blood type AB was associated with a 29% increased risk of stroke among men and women – 28% in women and 32% in men.  And blood type B was associated with a 15% increased stroke risk in women, but not in men.  Indeed, there was a decreased risk of stroke in group B men, but this was not statistically significant. 

It’s surprising that no one has discovered these associations between blood groups and stroke before. Of course, it probably doesn’t make too much difference to the way we live our lives - we can’t change our blood type.  And the findings are only associations, not cause-and-effect in nature.  Nevertheless, this information may help identify people at higher, though moderate, susceptibility to stroke, i.e. those who are group AB. They should check heir cardiovascular risk factors, and, if necessary, modify their lifestyle.