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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.

Selenium and the SEPP1 Gene: What Your Genotype May Mean for Health

Selenium is an essential trace mineral that plays a role in immune support, thyroid function, reproduction, and protecting cells as an antioxidant. The SEPP1 gene makes Selenoprotein P, a primary selenium transport protein that moves selenium to tissues such as the brain, kidneys, and thyroid. Variations in SEPP1 can influence how well selenium is distributed in the body, which may affect blood selenium levels and downstream functions that depend on the mineral.

Why selenium matters

  • Immune function: Selenium supports immune cell responses and antioxidant defense systems.
  • Thyroid health: The thyroid contains high selenium concentrations; selenium-dependent enzymes help activate and regulate thyroid hormones.
  • Reproduction: Selenium contributes to reproductive health in both sexes.
  • Antioxidant protection: Selenium is part of enzymes that neutralize harmful free radicals and reduce cellular damage.

General dietary guidance

To support healthy selenium status, emphasize a varied, nutrient-dense diet that includes selenium-rich foods. Safe and practical options include:

  • Brazil nuts: extremely rich in selenium. One or two nuts per day can significantly contribute to needs; avoid frequent large portions to prevent excess intake.
  • Seafood: tuna, sardines, shrimp, and other fish and shellfish.
  • Meats and poultry: beef, pork, chicken and turkey.
  • Eggs and dairy: provide modest selenium content.
  • Grains and legumes: whole grains, beans, lentils and certain cereals.

The Recommended Dietary Allowance for adults is 55 micrograms per day. Selenium is essential but can be harmful in excess, so supplements should only be used under the guidance of a healthcare professional.

Lifestyle and monitoring

  • Balance overall intake: combine food sources rather than relying on a single food to meet needs.
  • Limit high-dose supplements unless prescribed: excess selenium can cause symptoms such as gastrointestinal upset, hair loss, nail changes, and neurological effects.
  • Consider blood testing if concerned: serum selenium or selenoprotein measurements can clarify status when clinical questions arise. Discuss appropriate testing with your healthcare provider.
  • Supportive habits: maintain a balanced diet, regular physical activity, and manage stress to help overall nutrient utilization and antioxidant defenses.

Genetic interpretation for SEPP1 rs3877899

Two effect alleles (TT)

If you have the TT genotype for rs3877899, you carry two copies of the effect allele. This variation is associated with lower serum selenium levels in some studies. The SEPP1 gene produces Selenoprotein P, the main transporter of selenium to organs like the brain, kidneys, and thyroid. With the TT genotype this transport function may be less efficient, which could reduce circulating selenium availability.

Practical steps

  • Diet: Emphasize selenium-rich foods. Brazil nuts are a convenient source; limit to one or two nuts per day to avoid excess. Include seafood, meats, eggs, dairy, whole grains and legumes regularly.
  • Supplementation: Only consider supplements after discussing with your healthcare provider. If a provider recommends supplementation, they will advise an appropriate dose and duration while monitoring for excess intake.
  • Monitoring: Ask your provider about serum selenium testing or assessment of selenoprotein status if you have symptoms or risk factors for deficiency.
  • Lifestyle: Maintain a varied, nutrient-dense diet, avoid smoking, manage chronic conditions and ensure adequate protein and calorie intake to support nutrient transport and utilization.
One effect allele (CT)

If you have the CT genotype for rs3877899, you carry one copy of the effect allele. This variation is associated with likely lower serum selenium levels compared to individuals without the effect allele. Having one T allele may reduce the efficiency of Selenoprotein P production or function, possibly resulting in modestly reduced selenium transport and circulating levels.

Practical steps

  • Diet: Aim to include selenium-rich foods daily. Brazil nuts (one or two occasionally) are useful but consume in moderation. Add fish, seafood, poultry, meat, eggs, dairy and whole grains to meals.
  • Recommended intake: Adults generally target 55 micrograms per day from diet and supplements combined unless otherwise directed by a clinician.
  • Supplementation: Consider only if dietary intake is insufficient or testing shows low levels. Discuss dosage with a healthcare provider to avoid exceeding safe upper limits.
  • Monitoring and lifestyle: Consider periodic blood testing if you have symptoms or other risk factors. Support overall antioxidant status through balanced nutrition and healthy lifestyle choices.
No effect alleles (CC)

If you have the CC genotype for rs3877899, you carry two copies of the non-effect allele. This genotype is associated with typical serum selenium levels in most people. Your SEPP1 gene likely supports normal Selenoprotein P production and selenium transport throughout the body.

Practical steps

  • Diet: Continue a balanced diet with selenium-containing foods such as Brazil nuts in moderation, seafood, meats, eggs, dairy and whole grains.
  • Maintain recommended intake: Aim for the 55 microgram daily guideline from food and supplements combined unless your healthcare provider advises otherwise.
  • Supplementation: Not routinely needed if you eat a varied diet. Only use supplements when recommended by a provider and monitored appropriately.
  • Monitoring and lifestyle: Routine testing is not necessary based solely on this genotype, but discuss testing if symptoms or clinical signs suggest altered selenium status.

When to speak with your healthcare provider

  • If you experience symptoms that could relate to selenium imbalance, such as unusual fatigue, thyroid issues, hair or nail changes, or other unexplained signs.
  • If you are pregnant, planning pregnancy, breastfeeding, or have a chronic health condition that could affect nutrient status.
  • Before starting any mineral supplement, especially if you take multiple supplements or medications that might interact.
  • If you want personalized testing or interpretation of your selenium status in the context of your overall health.

PlexusDx provides educational information about genetic predispositions and how they may relate to nutrition and wellness. This content is not medical advice. Always consult your healthcare provider before starting supplements, making significant dietary changes, or if you have health concerns. Your provider can help interpret genetic results alongside your medical history, symptoms, medications and laboratory tests to guide safe, personalized care.

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 SEPP1 rs3877899

How might the SEPP1 rs3877899 genotype affect my selenium levels?

SEPP1 helps form Selenoprotein P, the main transporter that moves selenium to key organs like the brain, kidneys, and thyroid. For rs3877899, some genotypes are linked in studies to lower serum selenium—potentially reducing selenium availability for selenium-dependent antioxidant and thyroid-supporting functions.

What should I eat if I have the SEPP1 rs3877899 TT or CT genotype?

If you carry one or two effect alleles (TT or CT), practical guidance focuses on emphasizing selenium-rich foods to support antioxidant defense and thyroid health. Include Brazil nuts in moderation (typically one or two per day, not large frequent portions), plus seafood (tuna, sardines, shrimp), meats and poultry, eggs and dairy, and whole grains/legumes. Aim for the adult recommended intake of about 55 micrograms per day from food and supplements combined unless your clinician directs otherwise.

Should I get blood testing or consider selenium supplements based on my SEPP1 rs3877899 result?

You may consider testing and/or supplementation if you have symptoms suggestive of selenium imbalance (such as unusual fatigue, thyroid concerns, or hair/nail changes), have a higher-risk situation (pregnancy, chronic conditions), or if dietary intake may be insufficient. Blood testing (such as serum selenium or selenoprotein-related measures) can clarify status. Avoid high-dose selenium supplements unless prescribed, because excess selenium can be harmful; discuss dosing and monitoring with your healthcare provider.

What tests can help me learn more about Selenium and SEPP1 rs3877899?

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.