Link Between Blood Type and Heart Disease Risk Questionable

0 Shares

Reading time: 6 – 10 minutes

A new study published in the American Heart Association journal Arteriosclerosis, Thrombosis and Vascular Biology found that people with blood type A, B, or AB — 66% of the American population — had a higher risk for coronary heart disease compared to those with blood type O [1].

The findings are based on an analysis of two large U.S. studies — 62,073 women from the Nurses’ Health Study and 27,428 men from the Health Professionals Follow-up Study. Study participants were between ages 30 and 75, and both groups were followed for 20 years or more.

Heart disease, also called coronary heart disease (CHD) is a narrowing of the small blood vessels that supply blood and oxygen to the heart. CHD is also called coronary artery disease. Epidemiological data from previous research on the association between blood groups and risk of heart disease have been inconsistent. Researchers in the Department of Nutrition at Harvard School of Public Health in Boston, Massachusetts, decided to investigate the associations between ABO blood group and CHD risk in prospective cohort studies.

Prospective cohort study: a type of study that follows a group of similar individuals (called cohorts) over time who differ with respect to certain factors under study in order to determine how the factors affect rates of a certain outcome.

Scientists found that participant in the studies with AB, the rarest blood type, had the highest increased risk of heart disease risk at 23%. Those with type B blood type had an 11% increased risk, while those with type A had a 5% increased risk.

Researchers noted that the percentages of different blood types seen among the men and women enrolled in the two studies reflected levels seen in the general population. Since the study group was predominantly Caucasian, it’s not clear whether the findings will translate to other ethnic groups.

What’s your blood type?

There are four groups of human blood: A, B, AB and O. Each letter refers to the type of antigen on the surface of a person’s red blood cells.

Antigen: any substance that causes your immune system to produce antibodies against it.

Blood group antigens are either sugars or proteins, and are attached to various components in the membrane of red blood cells [2]. Each blood group is also classified by another type of antigen found on red blood cells: the Rhesus (Rh) factor. Blood groups are either Rh positive (Rh+) or Rh negative (Rh-). Thus, there are eight blood types [3]:

Blood type	Americans with this type	Compatible blood type(s)
O+	37.4%	O+, A+, B+, AB+
O–	6.6%	All blood types
A+	35.7%	A+, AB+
A–	6.3%	A+, A–, AB+, AB–
B+	8.5%	B+, AB+
B–	1.5%	B+, B–, AB+, AB–
AB+	3.4%	AB+
AB–	0.6%	AB+, AB–

So what does blood type have to do with heart disease risk? Perhaps nothing.

Some doctors doubt the link

On NPR’s Science Friday last week, host Flora Lichtman talked with Dr. Eric Topol, a cardiologist and director of the Scripps Translational Science Institute in La Jolla, California, who believes that the “dredging of data” — the practice of searching large volumes of data to find any possible relationship — has resulted in a false conclusion [5].

According to Dr. Topol,

[The correlation is] about a 10 percent effect of the, you know, so-called or putative protective effect of blood type O. [A] very small effect. And [the researchers] actually go back and look at the six other studies, cumulatively, and only half of them had any level of significance but very small effect. Beyond that, there’s a problem of why. There’s no real mechanism. There’s no real science behind this.

Indeed, the prospective cohort study did not evaluate the biological processes behind blood type and heart disease risk. In fact, the purpose of the two studies evaluated had little to do with blood type. The Nurses’ Health Study, established in 1976, was designed to investigate the potential long term consequences of the use of oral contraceptives. The Health Professionals Follow-up Study, established in 1986, was designed to evaluate a series of hypotheses about men’s health relating nutritional factors to the incidence of serious illnesses, such as cancer, heart disease, and other vascular diseases.

Dr. Topol suggests that instead of worrying about their blood type, people focus instead on well established drivers of heart disease, such as obesity, diabetes, smoking, high cholesterol, high blood pressure and sedentary (lack of exercise). These are risk factors that can be altered by adopting a healthier lifestyle, such as eating right, exercising and not smoking.

References

He et al. ABO Blood Group and Risk of Coronary Heart Disease in Two Prospective Cohort Studies. Arterioscler Thromb Vasc Biol. 2012 Sep;32(9):2314-20. Epub 2012 Aug 14.
View abstract
Laura Dean. Blood groups and Red Cell Antigens. National Center for Biotechnology Information (NCBI), National Library of Medicine, National Institutes of Health, Bethesda, MD 20892-6510.
Blood type may influence heart disease risk. American Heart Association. 2012 Aug 14.
Blood Types in the U.S. Stanford University School of Medicine Blood Center. Accessed 2012 Jul 11.
Some Docs Doubt Blood Type, Heart Disease Link. Talk of the Nation. NPR. 2012 Aug 17.