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Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

SEP15 and Selenium: What Your Genotype May Mean for Selenium Levels and Health

Selenium is an essential trace mineral that supports metabolism, immune function, thyroid health, and cellular protection through antioxidant selenoproteins. The SEP15 gene helps produce one of these selenoproteins, which is involved in maintaining protein quality in cells. Variations in SEP15 can influence how efficiently selenium is used and maintained in the body, sometimes resulting in higher serum selenium levels.

How to read this information

This article explains common SEP15 genetic results at the rs561104 position and practical, easy to follow lifestyle, diet, supplement, and testing suggestions to support healthy selenium status. PlexusDx does not provide medical advice. This information is educational only. Always talk with your healthcare provider before making changes to diet, supplements, or medical care.

Why selenium balance matters

Selenium is required in small amounts. It contributes to antioxidant defense, thyroid hormone metabolism, and immune response through selenoproteins. Low selenium can affect thyroid function and immune resilience. Too much selenium can cause symptoms such as gastrointestinal upset, hair and nail changes, and more serious toxicity at high levels. The generally recommended intake for most adults is about 55 micrograms per day, and most guidelines set an upper safe limit near 400 micrograms per day.

Genetic interpretations

2 effect alleles (CC) - higher serum selenium

You carry two copies of the effect allele at rs561104 (CC). This genotype is associated with higher serum selenium compared to other variants. The SEP15 variation may change how efficiently selenium is incorporated into selenoproteins or how it is metabolized, leading to naturally elevated circulating selenium.

  • Diet: Prioritize a balanced diet with selenium rich foods, but be cautious with extremely high sources. Good choices include seafood, lean meats, eggs, whole grains, and small amounts of Brazil nuts. Limit Brazil nuts to 1 to 2 nuts per day because they are very high in selenium.
  • Supplements: Avoid routine selenium supplements unless a healthcare provider recommends them. With a genetic tendency toward higher serum selenium, supplementation increases the risk of exceeding safe levels.
  • Lifestyle: Maintain a varied diet and avoid overreliance on fortified foods or multiple supplements that may contain selenium. Monitor any new supplements for selenium content.
  • Blood testing: Consider discussing a serum or plasma selenium test with your provider if you regularly eat high selenium foods or take supplements, or if you have symptoms of excess selenium. Testing can clarify whether your levels are in a healthy range.
  • When to seek care: Contact your clinician if you notice unexplained gastrointestinal symptoms, hair loss, brittle nails, or other changes that could suggest excessive selenium.
1 effect allele (CT) - likely higher serum selenium

You carry one copy of the effect allele at rs561104 (CT). This genotype is associated with likely higher serum selenium levels relative to those without the effect allele. Your SEP15 variation may modestly increase the efficiency of selenium incorporation into selenoproteins or slow selenium clearance.

  • Diet: Aim for balanced selenium intake from whole foods. Include seafood, poultry, eggs, beans, and grains. Limit Brazil nuts to 1 to 2 per day and avoid excessive intake.
  • Supplements: Use selenium supplements only under medical advice. If your diet already provides good selenium, supplemental selenium may not be necessary and could risk exceeding safe limits.
  • Lifestyle: Keep a food and supplement log for a short period if you are introducing new supplements or consuming Brazil nuts regularly. This helps estimate total selenium intake.
  • Blood testing: Consider baseline serum selenium testing if you are concerned about high intake, use supplements, or have thyroid concerns. Repeat testing after diet or supplement changes if recommended by your provider.
  • When to seek care: Report symptoms such as nausea, diarrhea, hair thinning, or nail changes to your clinician. These can be signs of excessive selenium and merit evaluation.
0 effect alleles (TT) - typical serum selenium

You carry two copies of the non-effect allele at rs561104 (TT). This genotype is associated with typical serum selenium levels, meaning your SEP15 variant does not appear to substantially alter selenium handling compared to the general population.

  • Diet: Meet recommended selenium intake through diverse foods. Good sources include Brazil nuts in moderation, seafood, lean meats, eggs, and whole grains.
  • Supplements: Most people with typical selenium status do not need supplements if they eat a varied diet. Consider supplementation only when advised by a healthcare professional, such as for diagnosed deficiency.
  • Lifestyle: A diet rich in plant and animal sources along with routine health screenings supports balanced selenium levels and overall health.
  • Blood testing: Test selenium if you have clinical concerns such as thyroid dysfunction, signs of deficiency, or if you follow a restricted diet that might limit selenium intake.
  • When to seek care: Speak with your healthcare provider if you develop symptoms consistent with deficiency such as fatigue, muscle weakness, or thyroid-related changes.

Practical tips to manage selenium intake

  • Eat a variety of selenium containing foods. Typical servings of fish, shellfish, poultry, eggs, and whole grains contribute to daily needs.
  • Limit Brazil nuts to 1 to 2 nuts several times per week or up to 1 per day depending on total dietary intake. One Brazil nut can provide a large fraction of daily selenium needs.
  • Check supplement labels. Selenium appears in some multivitamins and combination supplements. Add up total selenium from all sources to avoid exceeding the upper limit.
  • Consider targeted blood testing if you have risk factors for low or high selenium, if you consume high amounts of selenium foods regularly, or if your clinician recommends monitoring due to thyroid or other health conditions.
  • Balance with other nutrients. Selenium works with other antioxidants and with adequate protein intake to support selenoprotein synthesis.

Who may benefit from testing

  • People who regularly consume large amounts of Brazil nuts or highly selenium enriched foods.
  • People who take multiple supplements that may contain selenium.
  • Individuals with thyroid disease, unexplained changes in hair or nails, or symptoms that could indicate selenium imbalance.
  • Those with dietary restrictions that reduce intake of selenium rich foods.

Final notes and disclaimer

Genetic results describe tendencies based on your DNA. They do not diagnose disease and do not replace medical advice. PlexusDx provides educational information about genetic predispositions only. Always consult your healthcare provider before starting or stopping supplements, ordering blood tests, or making medical or dietary changes based on genetic information.

If this genetic variant is present in your PlexusDx results, the following tests and reports are commonly used to explore it further:

🧬 Genetic Tests:

🧪 Blood Tests:

📄 Genetic Report:

Frequently Asked Questions About Selenium and SEP15 rs561104

What does the SEP15 rs561104 genotype mean for my selenium levels?

SEP15 helps produce selenium-dependent antioxidant selenoproteins, and variations at rs561104 can influence how selenium is incorporated and maintained in the body. If you have two effect alleles (CC) or one effect allele (CT), your genotype is associated with likely higher serum selenium compared with the TT genotype, which is linked to typical selenium levels.

How much selenium should I aim for if my SEP15 result suggests higher serum selenium?

For most adults, the recommended selenium intake is about 55 micrograms per day, with an upper safe limit near 400 micrograms per day. If you’re CC or CT, focus on getting selenium from a balanced diet and avoid routine selenium supplements unless your healthcare provider recommends them, since higher genetic tendency plus added intake can increase the risk of exceeding safe levels.

When should I consider selenium blood testing with an SEP15 rs561104 effect allele?

Consider discussing a serum or plasma selenium test with your provider if you regularly eat high-selenium foods (especially Brazil nuts), take supplements that may contain selenium, have thyroid disease, or notice symptoms that could indicate excess selenium (such as gastrointestinal upset, hair loss, or brittle nail changes). Testing helps confirm whether your selenium level is within a healthy range.

What tests can help me learn more about Selenium and SEP15 rs561104?

The Optimal Diet and Weight Loss Genetic Test delivers over 295 genetic insights related to nutrition response, body composition, metabolism, and fitness. The Diet and Nutrition Genetic Report translates your results into personalized, actionable guidance. Your healthcare provider can also recommend targeted blood tests based on your specific pathway results and health history to complement your genetic insights with current biomarker data.

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.