FUT2 rs735983: Understanding Secretor Status and B12 Levels
The rs735983 variant is located within the FUT2 gene, which plays a key role in determining an individual's 'secretor status.' This genetic variation is statistically associated with differences in gut microbiome composition and circulating levels of vitamin B12.
What each genotype means
Typical secretor status
You carry two copies of the functional G allele, which is linked to normal FUT2 enzyme activity and typical secretion of ABO blood group antigens into mucosal secretions. Research associates this genotype with normal gut microbiota diversity, though it may confer lower average circulating serum vitamin B12 concentrations relative to non-secretors. This is a common statistical association and does not indicate vitamin deficiency or gastrointestinal illness.
Carried by approximately 25% to 30% of individuals of European descent, and generally more prevalent in African and East Asian ancestries.
Secretor carrier
You carry one copy of the secretor allele and one non-secretor allele, which typically provides sufficient FUT2 fucosyltransferase activity to express ABO antigens in bodily secretions. Studies suggest that individuals with this heterozygous genotype exhibit an intermediate microbiome profile and intermediate circulating vitamin B12 levels between homozygous secretors and non-secretors. This profile reflects common physiological variation rather than a clinical condition.
Carried by approximately 45% to 50% of individuals in European populations, representing the most common genotype.
Non-secretor status
You carry two copies of the non-secretor allele, which is in strong linkage with reduced or absent FUT2-mediated secretion of ABO antigens onto mucosal linings. Genome-wide studies link this genotype with altered gut microbiome composition and statistically higher circulating serum vitamin B12 levels. Evidence regarding functional gastrointestinal impacts remains limited and population-specific, and this genotype alone does not diagnose any health condition.
Found in roughly 20% to 25% of individuals of European descent, but occurs at significantly lower frequencies in East Asian populations.
What is the FUT2 Gene?
The FUT2 gene provides instructions for creating an enzyme called alpha(1,2)-fucosyltransferase. This enzyme is responsible for adding specific sugar molecules to proteins and lipids on the surface of cells, particularly in the mucosal linings of the digestive and respiratory tracts. These sugars form the basis of the ABO histo-blood group antigens in bodily secretions like saliva and mucus. Individuals who possess at least one functional copy of the FUT2 gene are referred to as 'secretors,' meaning they can secrete these blood group antigens into their bodily fluids. Those who inherit two non-functional copies of the gene are known as 'non-secretors.' This biological distinction is significant because these secreted sugars serve as a source of nutrition for certain commensal bacteria in the gut, potentially influencing the overall diversity and composition of the intestinal microbiome.
Understanding the rs735983 Variant
The rs735983 variant is a single nucleotide polymorphism (SNP) found within the FUT2 gene region. In the context of human genetics, SNPs are common variations where a single building block of DNA—a nucleotide—differs between individuals. While rs735983 is often studied alongside other well-known FUT2 variants like rs601338, it serves as a marker for understanding how genetic diversity in this gene influences physiological traits. Research indicates that variations in this region are linked to how the body processes and absorbs vitamin B12. Because the FUT2 enzyme is active in the gut, changes in its function may alter the environment of the digestive tract, which in turn can affect the absorption efficiency of essential nutrients. Scientists use these markers to investigate why individuals may have different baseline levels of B12, even when dietary intake is similar.
Research Associations and Evidence Strength
The evidence linking FUT2 variants to health-related traits is considered limited to moderate, as findings can vary significantly between different study populations. Multiple genome-wide association studies have identified a strong statistical link between FUT2 variants and plasma vitamin B12 levels. Some research suggests that non-secretors may have different B12 absorption profiles, which is a critical consideration for those monitoring their nutritional status. Additionally, the relationship between FUT2 and the gut microbiome has been a subject of intense study. While some early research suggested that secretor status significantly dictates the abundance of specific bacterial taxa, more recent and larger studies have produced mixed results, with some finding no significant association between genotype and fecal microbial diversity. This indicates that while the FUT2 gene is biologically relevant, its impact on the microbiome may be influenced by other environmental or genetic factors, making the current evidence base complex and evolving.
What You Can and Cannot Do With This Information
Genetic information regarding the FUT2 gene is primarily for educational purposes and should not be used to diagnose or treat any medical condition. If you are concerned about your vitamin B12 levels or digestive health, it is essential to consult with a healthcare professional or a registered dietitian. They can order appropriate blood tests to measure your actual B12 levels and provide personalized guidance based on your clinical history, diet, and symptoms. You cannot use your genotype to determine your nutritional needs or to predict your risk for specific diseases. Genetic associations are statistical observations across large groups of people and do not necessarily predict an individual's health outcome. Always discuss any changes to your diet, supplementation, or health management plan with a qualified clinician to ensure that your approach is safe and evidence-based.
How common is this variant?
The minor allele (A) for FUT2 variants is common in European populations, with a frequency typically ranging between 0.45 and 0.50.
Frequently asked questions
What does it mean to be a 'non-secretor'?
Being a non-secretor means you do not secrete ABO blood group antigens into your saliva, mucus, or other bodily fluids. This is determined by your genetics and is a normal variation found in about 20% of people of European descent.
Does my FUT2 genotype mean I have a vitamin B12 deficiency?
No, your genotype does not diagnose a deficiency. While certain FUT2 variants are associated with differences in circulating B12 levels, a blood test ordered by your doctor is the only way to determine if your B12 levels are clinically low.
Can I change my secretor status?
No, your secretor status is determined by your inherited DNA sequence and cannot be changed. It is a stable genetic trait that you are born with.
Should I take B12 supplements based on my FUT2 results?
You should not start or change any supplementation based solely on genetic results. Please discuss your B12 levels and any potential need for supplementation with your healthcare provider.
Sources & further reading
Educational information only, last refreshed 10/10/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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