Can blood type affect my blood sugar? Probably not
A handful of studies show correlations between blood type and diabetes risk, but so far, the research is too thin to suggest a real connection.
Blood sugar levels are influenced by a wide array of factors, ranging from diet and exercise to genetics and gut health. In recent years, emerging research has uncovered a number of surprising determinants that may play a role in dysregulated blood sugar and Type 2 diabetes, such as genetics, gut microbiomes, sleep disturbances, microplastics, and even cesarean sections.
A handful of studies have suggested that blood type may be one of these surprising influences on metabolic health. However, while some research has shown a tenuous connection between blood group and blood sugar regulation, taken as a whole, the current body of evidence indicates that the link, if any, is likely to be weak.
Here’s more on how blood types work and what the current research suggests.
What is blood type?
On the surface of our red blood cells are structures called “antigens,” which signal our body’s immune system to ward off infection. These antigens are composed of either carbohydrates, which are sugar molecules, or proteins, which consist of amino acids. Antigens on red blood cells fall into various blood group systems. Each system is linked to a single gene or a closely linked group of genes responsible for encoding a class of antigens. Variations in these genes, inherited from parents, result in differences in the sequence of sugars or proteins within an antigen. Each gene variation is called an allele, and we inherit one each from both parents.
This diversity means there is a wide range of unique antigens within a broad range of blood groups. Currently, scientists know of 45 blood group systems that collectively encode for 362 distinct antigens. Depending on our genetic variations, each of us will have some combination of zero, one, or multiple antigens from each blood group system on our red blood cells.
Technically, a person’s blood type refers to all their antigens across the various blood group systems. In practice, though, clinicians and researchers tend to only consider the antigens of two major systems when describing blood type: the ABO system and the Rh factor system.
In the ABO system, people can have either two A alleles, two B alleles, one A and one B allele, or in the case of Type O blood, neither A nor B alleles. The key difference between A and B antigens lies in their sugar sequence. In type A blood, the last sugar in the sequence making up the antigen is called N-acetylgalactosamine, whereas for type B blood, the final sugar added is called d-galactose. The difference a simple sugar can make is not trivial: Certain ABO blood types could place you at a higher risk of developing infectious, cognitive, metabolic, or vascular conditions. Recently, a 2023 study conducted at the Harvard-affiliated Brigham and Women’s Hospital, determined that SARS-CoV-2, the virus that causes COVID-19, is more likely to infect blood group A cells than O cells.
The ABO blood group system takes precedence over other systems when determining blood type because it is the most immunogenic, meaning it has the greatest potential to trigger our body’s immune response. This has significant clinical implications, particularly in blood transfusions: if a person with type A antigens receives donor blood containing type B antigens, the recipient’s immune cells will perceive the B antigens as foreign invaders and will attack.
The second blood group system of note is the Rh factor system. Currently, there are more than 50 known Rh antigens, which scientists hypothesize play a role in ion transport and maintaining red blood cell membrane integrity. However, we’re generally concerned with only one particular antigen in the system: the D antigen. The presence of an Rh D antigen is called Rh positive, while its absence is known as Rh negative. Much like with the ABO system, the D antigen is of note because of its immunogenicity.
The remaining 43 blood group systems are generally ignored when determining blood type. This leads to eight core blood types:
- A RhD positive (A+)
- A RhD negative (A-)
- B RhD positive (B+)
- B RhD negative (B-)
- AB RhD positive (AB+)
- AB RhD negative (AB-)
- O RhD positive (O+)
- O RhD negative (O-)
Does blood type impact blood sugar?
Given this diversity of blood types and the known impact they can have on health conditions, a small number of researchers in the past few decades have investigated whether these antigen differences also affect blood sugar regulation or diabetes risk. However, their findings are often contradictory and have generally been hampered by small sample sizes. So far, we have no reliable conclusion.
One such study that received modest attention post-publication is a 2014 paper featured in the journal Diabetologia. The investigators specifically looked into the relationship between Type 2 diabetes and ABO blood type, Rh factor type, and both ABO and Rh factor together using data on 82,104 French female teachers collected over more than two decades. Participants were matched for age, fasting glucose level, and blood collection location to adjust for potential confounding variables. At the end of the study, their analysis determined that women with type B blood were 21% more likely, and those with type A blood were 10% more likely, to develop Type 2 diabetes compared to women with type O blood. The researchers did not find an association between Rh factor alone and Type 2 diabetes risk. When accounting for both ABO and Rh factor combined, the investigators found B+ patients had a 35% higher risk of Type 2 diabetes as compared to O- patients. While this seems like a significant connection, the study did have notable drawbacks. In particular, the study subjects were drawn from a very specific population, which reduces the generalizability of the study findings to the general public..
Other studies have failed to replicate this finding. The authors of a 2018 study based in India gathered information on 1,316 people and found that blood group O and AB patients had a greater prevalence of T2D. More recently, in 2022, a group of Ethiopian academics conducted a systematic review and meta-analysis of 26 published studies investigating the association between Type 2 diabetes and blood type. The authors concluded that, based on the research they examined, people with blood type B were at a higher risk of developing diabetes, while group O was associated with a lower risk (the opposite of the earlier studies’ findings), and group A, group AB, and Rh factor showed no association at all. However, the authors found evidence of publication bias in studies comparing group B blood with other blood types. This suggests that selective reporting of study findings may contribute to an overestimation of the purported diabetes risk posed by group B blood. To that end, the study authors identified several studies hailing from Algeria, India, and Bangladesh that found no association between high blood sugar levels and any blood type whatsoever.
What mechanisms might connect blood type and blood sugar?
None of these studies specifically looked at causal mechanisms between blood type and blood sugar, but they offer some theories based on other research for a potential connection. One concerns a sort of bankshot through our gut microbiome. In a paper published in 2012, Finish scientists looked at whether the intestinal microbiome may differ based on blood type and found that certain bacteria had a preference for inhabiting the intestines of those with B antigens. The authors of the 2014 Diabetologia study used this research to suggest these blood-group-mediated changes in the microbiome could influence how a person processes sugar.
Other studies have looked instead at inflammation, which contributes to insulin resistance, a precursor to diabetes. Specific alterations in the ABO gene sequence correlate with two inflammatory markers: tumor necrosis factor α and soluble intercellular adhesion molecule.
What does this mean for me?
In short, probably nothing. Currently, it “doesn’t seem like the data are strong enough to warrant blood typing everybody for diabetes,” said Laura Alonso, MD, Chief of the Division of Endocrinology, Diabetes and Metabolism at NewYork-Presbyterian/Weill Cornell Medical Center and Director of the Joan and Sanford I. Weill Center for Metabolic Health. Dr. Alonso explained that even if certain blood types were found to have greater susceptibility to Type 2 diabetes, it likely wouldn’t alter existing clinical care practices. Additionally, blood type would still be only one of many factors that contribute to the development of diabetes. Characteristics such as family history, waist circumference, sedentary lifestyle, gestational diabetes, and race/ethnicity play a larger role in diabetes risk. Focusing on things you can control will have a greater impact on promoting metabolic health.
