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December 2, 2011

Blood Type May Be a Risk Factor of Stroke


Risk factors associated with stroke has 2 types in general: controllable and uncontrollable. Controllable risk factors like diabetes, high cholesterol, and smoking that can be avoided; whereas uncontrollable factors such as age, gender, and family history are usually unpreventable. Scientists now would like to add one more risk factor to the uncontrollable group—blood type. They consider that the chance of having a stroke may be increased in people with certain blood types.

Every person has one of four major blood types: A, B, AB, and O, which are determined by the presence or absence of certain antigens. An antigen is a substance that can induce an immune response. Blood type O is the most common blood group with a 62 percent in global distribution; while type AB is the smallest group that has only one percent. The other two groups: type A and AB constitute about 21 percent and 16 percent of the world population, respectively.

A research team recently presented its findings about the association between the blood type and stroke risk at the American Heart Association annual meeting in Florida, the United States. These researchers, led by the study author—Dr. Lu Qi, an assistant professor of both medicine at Harvard Medical School and nutrition at Harvard School of Public Health, analyzed data on about 62,000 women in the Nurses’ Health Study and nearly 28,000 men from the Health Professionals Follow-up Study. All participants were tracked for 20 to 26 years.

Researchers found that blood type AB was associated with a 29 percent increased risk of ischemic stroke among women and men. When compared to blood type O, type AB appeared to have a 28 percent higher risk of stroke in women and a 32 percent increased chance for having a stroke in men. Moreover, type B was related to a 17 percent increase of stroke risk in women, but not in men. As for blood type A, researchers could not find any link to an added stroke risk in either gender.

Although this study discovered the association between blood type and stroke, some scientists argue that it did not prove blood type is a cause of having a stroke. Furthermore, other doctors doubted that this study only took ages, physical activity levels, and smoking status into consideration while neglected some risk factors like cholesterol levels or diabetes. Thus, further intensive researches are needed to explain what makes the association between blood type and stroke.

Blood types with a an increased risk of stroke like type AB and B cannot be changed, just like other risk factors in the uncontrollable group. Even though this study still needs additional researches to support its findings, the information it provided help identifying people at a higher chance of having a stroke. Those people with the higher risk blood type should monitor their other risk factors of stroke more often and maintain a healthier lifestyle.