“How do I know if I’m a secretor or a non-secretor?”
If you’re a secretor, it means that your ABO blood type (A, B, AB, or O) is not only in your blood, but also in other body fluids like saliva and mucus. Whether you’re a secretor or not is caused by one particular gene, which you can figure out with DNA testing kits.
We actually don’t know much about how our “secretor status” affects everyday life. The most I can say is that it has been linked to some disease risks, which I’ll get into below!
A primer on blood type
When we talk about ABO blood types, we’re talking about different types of sugars that are stuck to the surface of red blood cells. These sugars are called antigens.
Our ABO blood type comes from a stretch of DNA (called the ABO gene) that has the instructions to make these different sugars. Depending on which instructions your DNA has, you’ll make a certain combination of these antigens - this creates your blood type!
If you’re interested in how we inherit our ABO blood type, take a look at this post.
Our blood type is based on the antigens that our red blood cells make and stick on their surface.
Taking your blood type beyond your blood cells
But here’s a twist: our blood cells aren’t the only cells reading the ABO gene. There are other parts of our body that can make these antigens too!
When red blood cells make antigens, they also need to read a gene called FUT1. Together, ABO and FUT1 make a “sticky” antigen. This antigen attaches to the surface of the red blood cells.
But when other cells make antigens, they read a different gene called FUT2. Together, ABO and FUT2 make a “soluble” antigen. This means the antigens can float around on their own – they don’t need to be stuck to a cell’s surface.
So what are these other cells that read FUT2? They’re any cells that make some type of body fluid. This includes the cells in our skin that make sweat, the cells in our mouth that make saliva, and the cells in our airway and digestive system that make mucus.
In red blood cells, the ABO and FUT1 genes work together to make “sticky” antigens, that stay on the cell surface. In secreting cells, the ABO gene instead works with the FUT2 gene to make a version of the antigen that’s free to float around in our body fluids.
Around 80% of people are secretors.1 For the other 20% who are non-secretors, their FUT2 gene has been interrupted by a mutation, so they can’t make the free-floating form of antigens.
So if you’re a secretor, there are cells in your mouth that release your blood-type antigens into saliva. And there are cells in your tear ducts that release your antigens into tears. And so on, for all of the fluids that your body makes!
Your blood type and your secretor status are independent, since they come from two separate genes (ABO and FUT2). So for example, being blood type A does not affect your chance of being a secretor.
Your secretor status might affect some immune responses
Figuring out the role our secretor status plays in our lives is tricky, especially when we still don’t even know how our blood type itself affects our health!
That said, there is a little bit of research that suggests that being a secretor (or not) affects how we respond to some infections.
Before I get into it, I should say that most of these results have only been found once or twice. To be sure of the effect of any gene, studies need to be repeated. We want to make sure we get the same results in many different groups of people before we get too excited!
Okay, with that disclaimer out of the way, here are some of the trends we see with secretor status:
Non-secretors seem to be less likely to get some stomach illnesses, like stomach flu and ulcers.2-4 The case is strongest for stomach flu: in those studies, all of the people who got sick were secretors, and none of them were non-secretors!
On the flip side, non-secretors seem to be more likely to get yeast infections.5 They also seem to be more likely to get pneumonia and meningitis.6,7
Being a non-secretor has also been connected to some autoimmune diseases. The link between being a non-secretor and having inflammatory bowel disease has the most support. But, there are also links between being a non-secretor and having psoriasis or type 1 diabetes.8-11
Is there a diet for your blood type?
When I was looking for information to help me answer this question, lots of websites popped up that were related to blood type diets. These are fad diets where you get lists of foods to eat and avoid, depending on your blood type and whether or not you’re a secretor.
Blood type diets are based on the idea that our ABO blood type and secretor status affect how we digest food. Although this is a really interesting idea, and it might even be true, right now there is no research showing that these diets work.
On the one hand, our secretor status has been linked to the bacteria that are living in our intestines. This is because some bacteria like to bind to or eat the blood-type sugars made in the intestine by secretors.
The bacteria in our intestines help us break down food and produce certain nutrients that we can’t make on our own. So, it actually makes a lot of sense that our secretor status could affect digestion.
But on the other hand, none of these diet companies have tested how well their products work on the people using them. Not only that, but independent studies have failed to get results when testing out these diets.12,13
This means that we still don’t really understand how our secretor status could affect digestion - so any diets built around this idea are missing some really important information.
Needless to say, I won’t be signing up for a blood type diet any time soon!
Ways of learning your secretor status
Even though knowing your secretor status probably won’t affect the choices you make every day, it’s still cool to learn more about our bodies and how they work!
You can figure out whether or not you’re a secretor through DNA testing. Some companies offer kits just for secretor status, but if you want more genetic bang for your buck you can figure it out from 23andMe results!
23andMe provides info on a genetic variant called rs601338, which is in the FUT2 gene. If you’re an ‘AA’, you’re a non-secretor. If you’re a ‘GA’ or ‘GG’, you’re a secretor.
- 80% of people are secretors: Kelly et al., “Sequence and Expression of a Candidate for the Human Secretor Blood Group α(1,2)Fucosyltransferase Gene (FUT2)”, J Biol Chem. (1995).
- Non-secretors have lower risk of Norovirus infection (stomach flu): Thorven et al., “A homozygous nonsense mutation (428G-->A) in the human secretor (FUT2) gene provides resistance to symptomatic norovirus (GGII) infections”, J Virol. (2005).
- Non-secretors have lower risk of Rotavirus infection (stomach flu): Imbert-Marcille et al., “A FUT2 Gene Common Polymorphism Determines Resistance to Rotavirus A of the P[8] Genotype”, J Infect Dis. (2014).
- Non-secretors have lower risk of H. pylori infection (stomach ulcers): Ikehara et al., “Polymorphisms of Two Fucosyltransferase Genes (Lewis and Secretor Genes) Involving Type I Lewis Antigens Are Associated with the Presence of Anti-Helicobacter pylori IgG Antibody”, Cancer Epidemiol Biomarkers Prev. (2001).
- Non-secretors have higher risk of yeast infections: Chaim et al., “Association of Recurrent Vaginal Candidiasis and Secretory ABO and Lewis Phenotype”, J Infect Dis. (1997).
- Non-secretors have higher risk of pneumonia: Blackwell et al., “Non-secretion of ABO blood group antigens predisposing to infection by Haemophilus influenzae”, Lancet. (1986).
- Non-secretors have higher risk of meningitis: Blackwell et al., “Non-secretion of ABO antigens predisposing to infection by Neisseria meningitidis and Streptococcus pneumonia”, Lancet. (1986).
- Being a non-secretor is linked to inflammatory bowel disease: Jostins et al., “Host-microbe interactions have shaped the genetic architecture of inflammatory bowel disease”, Nature. (2012).
- Being a non-secretor is linked to inflammatory bowel disease: McGovern et al., “Fucosyltransferase 2 (FUT2) non-secretor status is associated with Crohn’s disease”, Hum Mol Genet. (2010).
- Being a non-secretor is linked to Crohn’s disease and psoriasis: Ellinghaus et al., “Combined analysis of genome-wide association studies for Crohn disease and psoriasis identifies seven shared susceptibility loci”, Am J Hum Genet. (2012).
- Being a non-secretor is linked to type 1 diabetes: Smyth et al., “FUT2 Nonsecretor Status Links Type 1 Diabetes Susceptibility and Resistance to Infection”, Diabetes. (2011).
- Scientific reports that don’t support the Blood Type Diet: Cusack et al., “Blood type diets lack supporting evidence: A systematic review”, Am J Clin Nutr. (2013).
- Scientific reports that don’t support the Blood Type Diet: Wang et al., “ABO genotype, ‘Blood-Type’ diet and cardiometabolic risk factors”, PLOS ONE. (2014).
