The Link Between Blood Types and Risks of COVID-19, Cancer, and Other Diseases

Blood is categorized into four main types—A, B, AB, or O—based on the types of antigens present on the surface of red blood cells. Antigens are proteins found on red blood cells that trigger an immune response when encountering unfamiliar substances, such as certain bacteria, Dr. Douglas Eric Guggenheim, a physician at the Abramson Cancer Center at the University of Pennsylvania Hospital, explained in a 2020 Penn Medicine article.

Increased Risk of Viral Infections

A 2023 study from Harvard Medical School, published in the journal Blood, found that the SARS-CoV-2 virus, which causes COVID-19, preferentially targets type A blood cells.

“We show that the part of the SARS-CoV-2 spike protein that’s key to enabling the virus to invade cells displays affinity for blood group A cells, and the virus in turn also shows a preferential ability to infect blood group A cells,” Dr. Sean R. Stowell, of Harvard Medical School and Brigham and Women’s Hospital, said in a press release.

Other recent studies have explored the mechanisms linking blood type to susceptibility to SARS-CoV-2.  One study showed that levels of ACE2 protein, the receptor that the virus binds to for cell entry, were significantly higher in people with type A blood compared to other blood types. The researchers also found that the binding rate of the spike protein to red blood cells was highest in people with type A blood and lowest in people with type O.

Despite these associations, when assessing a person’s risk of severe SARS-CoV-2 infection, factors such as age and pre-existing chronic conditions, like heart disease, tend to have more significant effects on the risk of severe SARS-CoV-2 infection than blood type.

Increased Risk of Cancer

Pancreatic cancer is one of the deadliest types of cancer because it tends to grow quickly, can rapidly invade surrounding organs, and is often difficult to detect early. One study found a statistically significant association between ABO blood group and pancreatic cancer risk. Compared to people with type O blood, those with blood types A, AB, and B had a 32, 51, and 72 percent higher risk of developing pancreatic cancer, respectively.

Additionally, a comprehensive review found that people with type A blood were more susceptible to Helicobacter pylori, a known risk factor for stomach cancer, thus increasing their likelihood of developing the disease. In contrast, type O blood was associated with a lower risk of several cancers, including colorectal, gastric, and breast cancer.

Higher Risk of Other Serious Conditions

Blood type has been found to be associated with an increased risk of other several serious health conditions.

Increased Risk of Heart Disease

Blood type may also be linked to the risk of developing heart disease. A meta-analysis from the Harvard T.H. Chan School of Public Health, analyzing health data from nearly 90,000 individuals over more than 20 years, found that people with type O blood had the lowest risk of developing coronary heart disease. After adjusting for cardiovascular risk factors, participants with blood types A, B, and AB had an increased risk of coronary heart disease by 6, 15, and 23 percent, respectively, when compared to people with type O blood.

Increased Risk of Allergic Diseases

There is also a clear association between blood type and allergic diseases. A review found that people with type O blood were more prone to allergic rhinitis and asthma compared to those with non-O blood group. In contrast, people with non-O blood types had a higher likelihood of developing atopic dermatitis, with the highest prevalence among those with type B blood, followed by type A.

Increased Risk of Cognitive Impairment

Genetic factors linked to blood type may also influence brain function and memory decline. A 2014 cohort study published in the journal Neurology found that people with type AB blood had an 82 percent higher risk of developing cognitive impairment compared to people with other blood types.

The study also showed that people with higher levels of factor VIII—a blood-clotting protein—had a 24 percent increased risk of cognitive impairment. People with type AB blood tend to have higher levels of factor VIII than other blood types.

Increased Risk of Malaria

Plasmodium falciparum, the parasite responsible for severe malaria, is linked to human blood type. A 2015 study published in Nature Medicine found that a protein expressed by P. falciparum-infected red blood cells binds preferentially to the surface of type A red blood cells, suggesting a higher risk for people with that blood type.

However, a 2018 study published in Scientific Reports that tested the blood of 40 healthy donors showed that P. falciparum parasites preferentially invaded type O red blood cells over type A. This finding contrasts with the known protective effect of type O blood against severe malaria, highlighting the complexity of host-pathogen interactions.

Associations Between Blood Type and 49 Diseases

A large-scale study by Karolinska Institutet, a research-led medical university in Sweden, analyzed data from 5.1 million people using predictive modeling to assess outcomes across 1,217 disease categories. The findings revealed associations between the ABO blood group and 49 different diseases.