Blood Type Tied to Stroke Risk
By Chris Kaiser, Cardiology Editor, MedPage Today
Published: November 18, 2011
Action Points
■Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
■Explain that researchers have now found that blood type, particularly the ABO blood group is also related to the risk of stroke.
■Note that of the four blood types, AB was associated with the highest risk of stroke and that the mechanism behind the conferred higher risk of stroke with various blood types is unknown.
ORLANDO --
The conventional stroke risks such as hypertension and smoking are well known, but researchers have now found that blood type, particularly the ABO blood group, is also related to the risk of stroke.
In two cohorts with more than two million person-years of follow-up, men and women in the AB blood group were very significantly associated with a 26% increase for the risk of developing stroke compared with those with type O blood (95% CI 1.11 to 1.44), Lu Qi, MD, PhD, from Harvard School of Public Health, and colleagues found.
Compared with women with type O blood, women with type B had a marginally significant 15% higher risk of stroke, according to the study presented at the American Heart Association meeting here.
Qi is unsure of the mechanism behind the conferred higher risk of stroke with various blood types.
However, previous genetic studies have shown that blood types AB and B are associated with cardiovascular risk factors, such as endothelial dysfunction leading to coronary heart disease.
Other studies have shown an association between type A and increased LDL cholesterol levels and type B with increased cholesterol and systolic blood pressure.
But no studies have shown blood type to be associated with stroke risk, Qi told MedPage Today.
For this study, researchers analyzed data from two prospective longitudinal cohorts with 26 and 20 years of follow-up. The Nurses' Health Study (NHS) includes 61,973 women and the Health Professionals Follow-up Study (HPFS) includes 27,808 men.
Information on ABO blood group was self-reported, but has been shown to have a high degree of external validity, Qi said.
Data were adjusted for age, smoking, body mass index (BMI), alcohol intake, physical activity, aspirin use, ethnicity, family history of coronary heart disease, history of hypertension and high cholesterol and type 2 diabetes, menopausal status, and postmenopausal hormone use.
At least 93% of participants in each blood type group (O, A, B, A
were white. In both cohorts, the number of participants was greatest in O, followed by A, B, and then AB, which is consistent with the overall population, Qi said.
Baseline characteristics were similar in each cohort, with an average age of 46 for women and 53 for men, and average BMIs of 24 and 25 kg/m2 for women and men, respectively.
The average percentage of the history of disease in women and men, respectively, was as follows:
•Hypertension -- 15% and 22%
•High cholesterol -- 4.8% and 10.9%
•Type 2 diabetes -- 1.6% and 2.4%
•Family history of coronary heart disease -- 13% for both
In the NHS group, there was a total of 1,995 participants who developed stroke, while in the HPFS group, 906 participants developed stroke.
Although women with type B had a 15% increase in stroke risk (RR 1.15, 95% CI 1.00 to 1.32), no such risk appeared in the male cohort (RR 0.84, 95% CI 0.68 to 1.08).
"In fact, in men, the association between type B was not significant, and the stroke risk appears to go in the opposite direction. It looks like there is a decrease in risk," Qi said.
Both of these results "surprised" researchers. Qi said the increased risk for women could be due to the larger sample size compared with men or to chance.
The decreased risk in men was also surprising because, in other studies, men with type B blood were associated with increased coronary heart disease and myocardial infarction.
"It's difficult to believe this blood group has a lower risk of stroke," he said.
In the combined multivariate analysis, the risk of ischemic stroke in group AB was greater than for hemorrhagic stroke compared with group O (RR 1.30, 95% CI 1.12 to 1.50 versus RR 1.20, 95% CI 0.79 to 1.82).
The study was limited by the population being mostly white, and it was underpowered to detect the associations with the subtypes of stroke such as hemorrhagic.
Qi said the next step is to determine whether lifestyle factors impact the stroke risk conferred by blood type.
The authors reported they had no conflicts of interest.
Primary source: American Heart Association
Source reference:
Qi L, et al "ABO blood group and risk of stroke in US men and women" AHA 2011; Abstract 16887.
http://www.medpagetoday.com/MeetingCoverage/AHA/29804?
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