The exact mechanism behind the increased heart risk isn’t exactly clear. But one possibility may be because people with non type-O blood have greater concentrations of a blood clotting protein called von Willebrand factor, which can make the development of a blockage that causes a heart attack more likely, the researchers say in a press release. (That also may be why guys with non type-O blood are more likely to develop erectile dysfunction, too.)
People with non-O blood also tend to have higher cholesterol and higher levels of inflammation.
More research is needed to clarify the links between blood type and heart risks—and to look at each blood type separately—but the researchers believe that blood type may eventually play a role in risk assessment for heart disease, along with traditional factors like cholesterol, age, and blood pressure.