A study published online in Arteriosclerosis, Thrombosis and Vascular Biology, a journal of the American Heart Association, reports an association between a person's blood type (A, B, AB or O) and the likelihood he or she will develop coronary heart disease (CHD).
Researchers at the Harvard School of Public Health in Boston reviewed data from two large studies -- the Nurses' Health Study, which included 62,000 women ages 30 to 55, and the Health Professionals Follow-up Study, which included 27,000 men ages 40 to 75. People in the studies were followed for at least twenty years and had answered questions on blood type as well as activity level, whether they smoked, used aspirin, or had a history of diabetes, high blood pressure or high cholesterol, for example. Subsequent surveys determined whether they had suffered a heart attack.
By analyzing the study data, the researchers showed that people with the non-O blood types A, B or AB were somewhat more likely to develop coronary heart disease than people with type O blood, although what causes the association is not yet clear and more research is needed, say the authors. Previous studies had suggested the link between blood type and heart disease but were small and the findings were inconsistent. The participants in the Nurses' Health Study and the Health Professionals Follow-Up Study were largely Caucasian, so the researchers say the findings cannot be extrapolated to other groups.
Associations, such as those reported in these studies, do not point to a specific biologic process that links CHD to the molecules that define a blood type. The researchers noted that the gene for blood type is often found in close proximity to genes that code for proteins involved in inflammation and cell adhesion, two processes that contribute to the development of CHD. Blood type may simply be a indicator of the presence of other genes.
In addition, Dr. Qi noted, there may be "multiple mechanisms at play." For example, the study mentions that blood levels of complexes of factor VIII and von Willebrand factor, two proteins involved in blood clotting, have been found to be about 25% higher in people with non-O blood type. Von Willebrand factor is thought to play a role in atherosclerosis.
Another mechanism that could be related is cholesterol levels. According to the American Heart Association, there is evidence suggesting that type A is associated with higher levels of low-density lipoprotein cholesterol (LDL-C), the so-called "bad cholesterol" that can clog arteries, and type AB is linked to inflammation, which may have an adverse effect on blood vessels. Blood types are genetically determined, and evidence from some genetics studies point to a link between ABO blood groups and heart disease risk, say the researchers.
"While people cannot change their blood type, our findings may help physicians better understand who is at risk for developing heart disease," said Lu Qi, M.D., Ph.D., the senior author of the study and an assistant professor in the Department of Nutrition at the Harvard School of Public Health in Boston. "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," says Dr. Qi.
Approximately 48% of Americans have type O blood, according to AABB (formerly the American Association of Blood Banks), and only about 4% have type AB blood. About 37% of Americans are blood type A, while 11% are blood type B. However, these rates vary for specific populations such as Hispanics and people of African or Asian descent, according to the American Red Cross. (For details, see the American National Red Cross: Blood Types.)
"The best way to find out your blood type is to ask your doctor to specifically do blood work to determine the type during a routine checkup, since it is not part of routine blood testing," says Peter Emanuel, MD, Chair of the Winthrop P. Rockefeller Cancer Institute at the University of Arkansas for Medical Sciences in Little Rock and Chair of the American Society of Hematology (ASH) Committee on Communications. People who donate blood will find out their blood type by mail within four to six weeks of the donation, according to Karen Stecher, a communications officer with the American Red Cross.
Aside from the benefit of helping others through blood donation, it could be worth the effort to find out. You could have one more piece of information about your risk for heart disease, as well as learn your blood type—important for health personnel to know in an emergency and for when a specific call goes out for blood donors with your type.
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Qi L, et al. ABO Blood Group and Risk of Coronary Heart Disease in Two Prospective Cohort Studies. Arterioscler Thromb Vasc Biol. 2012; 32:2314-2320, published online before print August 14 2012. Available online at http://atvb.ahajournals.org/content/32/9/2314.full through http://atvb.ahajournals.org. Accessed September 6, 2012.
(August 14, 2012) Petrochko, Cole. Type O Blood Carries Lower CHD Risk. Medpage Today. Available online at http://www.medpagetoday.com/Cardiology/MyocardialInfarction/34205 through http://www.medpagetoday.com. Accessed September 6, 2012.
(August 17, 2012) Paddock, Catherine. Blood Type May Affect Heart Disease Risk. Medical News Today. Available online at http://www.medicalnewstoday.com/articles/249071.php through http://www.medicalnewstoday.com. Accessed September 6, 2012.
(August 14, 2012) Blood Type May Influence Heart Disease Risk. News release, American Heart Association. Available online at http://newsroom.heart.org/pr/aha/blood-type-may-influence-heart-237373.aspx through http://newsroom.heart.org. Accessed September 6, 2012.
©2012 AABB. Blood FAQ. Available online at http://www.aabb.org/resources/bct/Pages/bloodfaq.aspx through http://www.aabb.org. Accessed September 6, 2012.
©2012 American National Red Cross. Blood Facts and Statistics. Available online at http://www.redcrossblood.org/learn-about-blood/blood-facts-and-statistics through http://www.redcrossblood.org. Accessed September 6, 2012.
©2012 American Heart Association. Understand Your Risk of Heart Attack. Available online through http://www.heart.org. Accessed September 6, 2012.
Quote from Dr. Emanuel sent in an email from A. Slesenski, communications office for American Society of Hematology, September 4, 2012.
Telephone interview with Karen Stecher, American Red Cross, September 4, 2012.