Blood type may affect stroke risk

New research suggests that the risk for stroke risk is tied to blood type, with men and women with type AB and women with type B at greater risk than people with type O.


The research can't prove the link. But it fits with other studies tying A, B and AB to heart attacks and blood clots in the legs. And type O has been tied to a heightened risk for bleeding, which implies less chance of the clots that are responsible for most strokes.


"There's increasing evidence that blood type might influence risk of chronic disease," said one of the study leaders, Dr. JoAnn Manson, chief of preventive medicine at Harvard's Brigham and Women's Hospital. "It's not at the level where we want to alarm people and we want to make that clear. But it's one more element of risk that people would want to know about," and it could encourage them to keep watch on their keep blood pressure and cholesterol, she said.


The study, led by Brigham's Dr. Lu Qi, was presented Wednesday at a meeting of the American Heart Association. It involved 90,000 men and women in two observational studies that have gone on for more than two decades.


Looking at the 2,901 strokes that have occurred during that time and taking high blood pressure and other stroke risk factors into account, researchers found that men and women with AB had a 26 percent higher risk of stroke compared to those with type O and that women with type B blood had a 15 percent greater risk compared to women with type O.


You can't change it, and we don't know if it's the blood type per se or other genes that track with it" that actually confers risk, said Dr. Larry Goldstein, director of Duke University's stroke center.
"There are other things that are more important" than blood type for stroke risk, such as smoking, drinking too much and exercising too little, he said.
About 45 percent of whites, 51 percent of blacks, 57 percent of Hispanics and 40 percent of Asians have blood type O, according to the American Red Cross. Such people are called "universal donors" because their blood can safely be used for transfusions to any other blood type.
AB blood type is the least common type, present in 4 percent of whites and blacks, 2 percent of Hispanics and 7 percent of Asians.
B is second least common overall, in 11 percent of whites, 19 percent of blacks, 10 percent of Hispanics and 25 percent of Asians.
A is in 40 percent of whites, 26 percent of blacks, 31 percent of Hispanics and 28 percent of Asians.