A non-secretor is an individual whose body does not release specific ABO blood group antigens into their bodily fluids, such as saliva, tears, and mucus. These antigens are sugar molecules expressed beyond red blood cells. Approximately 20% of the population, particularly those of European descent, are considered non-secretors.
The Genetic Basis of Secretor Status
A “secretor” is someone whose body secretes ABO blood group antigens into various bodily fluids like saliva, tears, breast milk, and gastrointestinal secretions. In contrast, a non-secretor lacks this ability, meaning these antigens are primarily found only on their red blood cells. This difference arises from variations in a specific gene called FUT2.
The FUT2 gene provides instructions for an enzyme that builds sugar molecules, including the H antigen, which is a precursor to the ABO blood group antigens, on proteins lining various tissues and in bodily fluids. Being a non-secretor is a recessive genetic trait, meaning an individual must inherit two non-functional copies of the FUT2 gene, one from each parent, to exhibit this status. While secretor status involves ABO blood group antigens, it is a separate genetic system from the ABO gene itself, which determines a person’s blood type.
Health Profile of a Non-Secretor
The absence of secreted blood group antigens in non-secretors influences several physiological aspects, particularly affecting the gut microbiome and immune responses. This distinct internal environment leads to specific health predispositions.
Gut Microbiome
The absence of secreted antigens alters the composition of non-secretors’ gut bacteria. These antigens normally serve as a food source for beneficial microbes, especially Bifidobacteria. Non-secretors often have lower levels of these beneficial bacteria and may exhibit lower microbial diversity. Their gut environment can become less hospitable for favorable bacteria to flourish, potentially allowing more detrimental bacteria, like Pseudomonas aeruginosa, to occupy space.
Immune System and Pathogen Susceptibility
Non-secretor status is linked to altered susceptibility to certain infections. Non-secretors generally show increased resistance to common strains of Norovirus, particularly the widespread GII.4 strains, which utilize blood group antigens to bind to cells. The absence of these antigens on mucosal surfaces prevents the virus from attaching and infecting cells. However, non-secretors may be more susceptible to other infections, such as Helicobacter pylori, a bacterium linked to stomach ulcers and certain types of stomach cancer.
Autoimmune Conditions
Correlations have been observed between non-secretor status and an increased risk for certain autoimmune conditions. This includes inflammatory bowel diseases like Crohn’s disease, celiac disease, and Type 1 diabetes. The altered gut microbiome in non-secretors, characterized by lower beneficial bacteria and potential sub-clinical inflammation, is thought to contribute to these increased risks.
Nutrient Absorption
Non-secretor status has also been associated with influences on nutrient absorption, particularly regarding vitamin B12. Non-secretors tend to have higher circulating levels of vitamin B12 in their blood plasma compared to secretors, with reported increases ranging from 10-25%. This difference is thought to be related to how vitamin B12 is transported and recycled in the body, potentially involving haptocorrin, a protein that binds vitamin B12 and is influenced by fucosylation from the FUT2 gene.
Dietary and Lifestyle Support
Understanding non-secretor status can inform dietary and lifestyle choices aimed at supporting overall well-being. The focus is on nurturing a healthy gut microbiome and strengthening immune function, given the physiological differences associated with this genetic trait.
Incorporating prebiotic-rich foods into the diet can help nourish beneficial gut bacteria. Foods such as onions, garlic, asparagus, tomatoes, bananas, and Jerusalem artichokes contain oligosaccharides and other soluble fibers that support the growth of favorable microbes like Bifidobacterium. A diverse intake of fiber from various plant sources contributes to a robust and balanced gut environment, which is particularly beneficial for non-secretors who may have lower levels of certain beneficial bacteria.
Probiotic supplements, especially those containing Bifidobacterium strains, may offer additional support for non-secretors by directly increasing the abundance of helpful bacteria in the gut. Some research suggests that supplementation with human milk oligosaccharides (HMOs), such as 2′-fucosyllactose (2’FL), which non-secretors cannot produce, could be beneficial for gut health and immune support. While certain named diets, like the Blood Type Diet, consider secretor status, the emphasis for non-secretors should remain on general wellness principles that support gut and immune health.
How to Determine Secretor Status
Determining one’s secretor status is a straightforward process, primarily relying on genetic analysis or, less commonly, on direct fluid testing. The most common modern method involves consumer genetic testing kits, such as those offered by 23andMe or AncestryDNA. These services analyze an individual’s DNA for specific genetic markers, known as single nucleotide polymorphisms (SNPs), within the FUT2 gene.
Users can often access their raw genetic data and look for particular SNPs, such as rs601338, to determine their secretor status. A genotype of “AA” at this locus typically indicates non-secretor status, while “GA” or “GG” indicates secretor status. A more traditional method involves a saliva test, which checks for the presence of A, B, or H antigens in the saliva using serologic techniques. If these antigens are not detected, the individual is classified as a non-secretor.