Secretor status (norovirus resistance & B12)

The FUT2 gene decides whether you release your blood-group sugars onto your gut lining and other body surfaces (this is called your secretor status). People who don't release them (non-secretors) resist many common stomach-flu noroviruses and tend to have higher vitamin B12.

What secretor status means

FUT2 attaches a sugar, part of the ABO blood group system, to the surface of cells lining the gut, airway and other mucosal surfaces, and to the fluids they secrete. People with two non-functional copies are non-secretors: their blood group antigens stay on red cells but do not appear on mucosal surfaces or in saliva.

About one in five people of European ancestry are non-secretors. It causes no illness, and for most of history it was invisible. What it changes is which microbes can attach to your gut lining, because several of them use those sugars as docking sites.

Norovirus resistance is the headline

Norovirus, the cause of most winter vomiting outbreaks, binds these sugars to enter gut cells. Non-secretors are resistant to the dominant GII.4 strains that cause the majority of outbreaks, which is one of the clearest examples of a common human variant conferring infection resistance.

It is resistance rather than immunity. Other norovirus strains use different binding patterns and can still infect non-secretors, so this is not a licence to ignore an outbreak on a cruise ship.

What else follows from it

Secretor status shapes the gut microbiome, particularly bifidobacteria, which use these sugars. It also affects measured vitamin B12: in a study of 442,192 people this variant was associated with B12 levels, and non-secretors tend to show higher readings, which reflects transport and binding rather than better B12 status.

There are smaller associations in both directions, including a slightly higher risk of Crohn's disease and type 1 diabetes in non-secretors and altered susceptibility to Helicobacter pylori and some other infections. None of these are large enough to act on.

The ancestry gap in this test

The non-functional variant read here is the common European one. In 1000 Genomes reference data it is absent from East Asian samples, where non-secretor status is instead caused by a different FUT2 variant that this file does not read.

So a secretor result in someone of East Asian ancestry carries much less information than the same result in someone of European ancestry.

What each rs601338 genotype means

rs601338 has three possible genotypes: GG, AG and AA.

Secretor type (rs601338 GG). You're a secretor: you release blood-group sugars onto the lining of your gut and other surfaces. One practical effect is that you're susceptible to the common noroviruses behind most stomach flu, and you tend to have somewhat lower vitamin B12 levels.

Secretor type (rs601338 AG). You carry one working copy of FUT2, which is enough to make you a secretor. You release blood-group sugars onto body surfaces, so you have typical norovirus susceptibility and B12 levels for a secretor.

Non-secretor type (rs601338 AA). You're a non-secretor: you don't put blood-group sugars on your gut lining. A neat side effect is that you resist many of the common noroviruses that cause stomach flu, and you tend to have higher vitamin B12 levels. Protection isn't total, since some norovirus strains get around it.

Evidence & sources

Across global populations, about 22% of people carry two copies of this variant, and about 31% carry none.

This variant appears in 1 published genetic study: PubMed 39024449.

Common questions

Does being a non-secretor mean I cannot catch norovirus? It means strong resistance to the dominant GII.4 strains behind most outbreaks, not immunity. Other strains bind differently and can still cause infection.

Does this affect my B12 levels? It shifts the measurement more than the status. Non-secretors tend to show higher measured B12 for reasons of binding and transport, so a B12 result should be interpreted clinically rather than as proof of better or worse B12 nutrition.

Related

Adult lactose digestion · Alcohol response (flushing & dependence risk) · Folate metabolism (MTHFR gene) · LDL cholesterol · Sweet tooth / carbohydrate preference (FGF21) · Triglycerides · Vitamin D status (low-D genetic burden)