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In a large study, researchers have found that people's blood types might have an effect on their heart disease risk. People with blood type A, B, or AB had a higher risk for coronary heart disease  when compared to those with blood type O. 

The research was published in Arteriosclerosis, Thrombosis and Vascular Biology, an American Heart Association journal.

Researchers analyzed two large studies that that followed nearly 90,000 people for more than 20 years. The participants were between ages 30 and 75, and their diet, age, body mass index, gender, race, smoking status, menopause status and medical history were factored.  

In the United States, 45 percent of people have type O blood, making it the most common blood type. Only 4 percent of the U.S. population has type AB blood, while about 40 percent has type A and about 11 percent has type B.

Researchers say their findings may help doctors better understand who is at risk  for developing heart disease. 

"It's good to know your blood type the same way you should know your cholesterol or blood pressure numbers," Lu Qi, the study's senior author, said. "If you know you're at higher risk, you can reduce the risk by adopting a healthier lifestyle, such as eating right, exercising and not smoking. Blood type is very complicated, so there could be multiple mechanisms at play

The team of researchers say their findings suggest that type A is associated with higher levels of low-density lipoprotein cholesterol, the waxy substance that can clog arteries, and type AB is linked to inflammation, which may affect the function of the blood vessels. Also, a substance that plays a favorable role in blood flow and clotting may be higher in people with type O blood. 

Understanding blood type could help healthcare providers better tailor treatments, Qi suggested. For example, a patient with type A blood may best lower heart disease risk by decreasing cholesterol intake.

The study group was predominantly Caucasian, and it's not clear whether these findings would translate to other ethnic groups. Environment also contributes to risk, Qi said.

"It would be interesting to study whether people with different blood types respond differently to lifestyle intervention, such as diet," Qi said, noting that further analysis is needed.