The senior author of the study is Lu Qi, an assistant professor in the Department of Nutrition at the Harvard School of Public Health in Boston. He and his colleagues report their findings in a paper published online this week in Arteriosclerosis, Thrombosis and Vascular Biology, one of the American Heart Association journals.
Qi and colleagues analyzed data from two large studies that followed adults for at least 20 years and found those with blood type AB had a 23% increased risk for heart disease, those with type B had an 11% increased risk, and those with type A had a 5% increased risk, compared to people with type O.
Blood type AB is the rarest blood type, it occurs in around 7% of Americans, while type O, the most common, occurs in around 43%.
Possible Reasons Not ExploredThe researchers did not look into the mechanisms that cause blood type to affect heart disease risk, but evidence from other studies gives some clues.
Blood type A is linked to higher levels of low-density lipoprotein (LDL) cholesterol, the "bad" cholesterol that clogs up arteries.
Blood type AB is linked to inflammation, which can affect how blood vessels work.
And people with blood type O have higher levels of a compound that has a beneficial effect on blood flow and clotting.
But, as Qi suggests in a press statement, it is unlikely to be as straightforward as this:
"Blood type is very complicated, so there could be multiple mechanisms at play," he says.
Nearly 90,000 Participants for 20 YearsFor the study, the team examined data covering nearly 90,000 participants aged from 30 to 75 who were followed for 20 years or more in two large well-known American studies: the Nurses' Health Study (62,073 women), and the Health Professionals Follow-Up Study (27,428 adults).
The proportions of men and women in the studies with various blood types were the same as in the general population, and the researchers were able to control for a number of factors that can affect health and heart disease risk, such as age, gender, race, body mass index, diet, smoking, menopause and medical history.
However, the participants were mostly Caucasian, so it's not clear whether the results would be the same for other ethnic groups. Environment also affects risk, says Qi.
ImplicationsAlthough people can't change their blood type, there are things they can do to reduce risk for heart disease.
Qi says it's important to know your blood type, just as it's good to know your cholesterol and blood pressure levels.
"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," he explains.
Also, armed with findings like these, health care providers can tailor treatments more effectively. For instance, patients with blood type A could be advised to reduce cholesterol in their diet to lower their risk of heart disease, says Qi, who suggests further studies should now be done to look at the effect of diet and lifestyle changes on heart disease risk in people with different blood types.
Funds from the National Institutes of Health, the American Heart Association Scientist Development Award and the Boston Obesity Nutrition Research Center helped finance the study.
Written by Catharine Paddock PhD