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.

FAM9B and Testosterone: What Your Genes May Mean for Energy, Mood, and Fertility

Testosterone is a key male hormone that helps regulate energy, mood, libido, muscle mass, and fertility. The FAM9B gene is active mainly in the testes and helps influence testosterone production and sperm development. Variations in this gene can shift average testosterone levels, so some men are genetically predisposed to lower levels and may experience symptoms such as fatigue, low mood, reduced libido, or decreased muscle mass.

How to Read This Result

This report explains how the rs5934505 variant in the FAM9B gene relates to testosterone. The effect allele at this location is associated with lower free and serum testosterone. Below you will find clear, actionable steps to support healthy testosterone and fertility whether or not you carry the effect allele.

Common Signs of Lower Testosterone

  • Persistent fatigue or low energy
  • Lowered libido or sexual dysfunction
  • Difficulty building or maintaining muscle mass
  • Mood changes such as low motivation or irritability
  • Concerns about fertility or sperm quality

General Lifestyle and Dietary Recommendations

Regardless of genotype, the following strategies support healthy testosterone production and overall reproductive health.

  • Protein and balanced macronutrients

    Prioritize high-quality protein at each meal: lean meats, fatty fish, eggs, and legumes. Protein supports muscle mass and hormone production. Include healthy carbohydrates around workouts and moderate healthy fats (olive oil, avocado, nuts) to support hormone synthesis.

  • Zinc- and magnesium-rich foods

    Include pumpkin seeds, shellfish, beef, spinach, nuts, and leafy greens. Zinc is important for testosterone production and sperm health. Magnesium supports sleep quality and muscle recovery.

  • Healthy fats

    Dietary cholesterol and saturated fat in moderation are precursors for steroid hormones. Include fatty fish, eggs, avocados, and nuts to provide building blocks for testosterone.

  • Strength training and physical activity

    Regular resistance training 2 to 4 times per week supports muscle mass, raises testosterone acutely, and improves body composition. Include compound movements such as squats, deadlifts, presses, and rows.

  • Sleep and circadian support

    Aim for 7 to 9 hours of consistent, high-quality sleep nightly. Morning sunlight exposure helps set circadian rhythms and supports healthy hormone cycles.

  • Reduce exposures that disrupt hormones

    Avoid unnecessary contact with plastics and common endocrine-disrupting chemicals. Use glass or stainless steel for food storage, avoid heating food in plastic, and reduce household products with synthetic fragrances when possible.

Targeted Supplements and Considerations

Supplements can help in specific situations but consult your healthcare provider before starting any new supplement, especially if you have medical conditions or take medications.

  • Ashwagandha — may support stress resilience and healthy testosterone in some men.
  • Boron — small doses have been associated with modest increases in free testosterone in some studies; use under professional guidance.
  • Zinc and magnesium — consider correcting deficiencies first through diet; supplements can be useful when blood tests confirm low levels.
  • Vitamin D — maintain adequate vitamin D status; low vitamin D can correlate with lower testosterone.

Testing and Medical Follow-up

If you experience persistent symptoms, talk with your healthcare provider about targeted testing. Typical tests include morning total and free testosterone, sex hormone binding globulin (SHBG), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, and vitamin D, zinc, and magnesium levels. Regular labs help guide personalized interventions and identify treatable causes.

Two effect alleles (TT) — rs5934505

If you have the TT genotype for rs5934505, you carry two copies of the effect allele. This variant in the FAM9B gene, which is primarily expressed in the testes, is associated with lower free and serum testosterone levels. Men with this genotype have a genetic predisposition toward reduced testosterone. This may show up as fatigue, mood changes, decreased libido, or reduced muscle mass.

Recommended actions

  • Prioritize a high-protein diet including lean meats, fatty fish, eggs, and legumes.
  • Eat zinc-rich foods such as pumpkin seeds, oysters, and shellfish; include spinach and nuts for magnesium.
  • Maintain consistent 7 to 9 hours of quality sleep and seek morning sunlight daily.
  • Avoid endocrine-disrupting plastics and reduce exposure to household chemicals that may affect hormones.
  • Engage in regular resistance training focused on progressive overload to preserve and build muscle mass.
  • Discuss targeted supplements like ashwagandha or boron with your healthcare provider and check nutrient levels before supplementing.
  • Consider baseline and follow-up lab testing of testosterone, SHBG, LH, FSH, vitamin D, zinc, and magnesium to guide care.
One effect allele (CT) — rs5934505

If you have the CT genotype for rs5934505, you carry one copy of the effect allele. The FAM9B gene influences testosterone production and sperm development. Your CT genotype is associated with likely lower free testosterone levels compared with CC. This genetic predisposition may contribute to symptoms such as fatigue, mood changes, reduced libido, or decreased muscle mass.

Recommended actions

  • Focus on a high-protein diet with lean meats, fish, eggs, and legumes to support muscle and hormone synthesis.
  • Include zinc-rich foods like pumpkin seeds and shellfish and magnesium-rich foods such as leafy greens, nuts, and whole grains.
  • Aim for regular strength training and include healthy fats for hormone building blocks.
  • Prioritize 7 to 8 hours of quality sleep and daily morning sunlight exposure.
  • Avoid plastics and other endocrine-disrupting substances when possible.
  • Consider checking nutrient and hormone levels with your healthcare provider before starting supplements.
No effect alleles (CC) — rs5934505

If you have the CC genotype for rs5934505, you carry two copies of the non-effect allele. This genotype is associated with typical testosterone levels. With the CC genotype you are not genetically predisposed to lower testosterone from this specific variant. Individuals with this genotype generally maintain normal testosterone production capacity.

Recommended actions

  • Continue healthy habits that support testosterone: adequate protein, zinc and magnesium-rich foods, and healthy fats.
  • Maintain regular resistance training and good sleep hygiene, including morning sunlight exposure.
  • Avoid unnecessary exposure to endocrine-disrupting chemicals in plastics and household products.
  • Use routine checkups and testing as needed if symptoms arise; genetics are one piece of a larger health picture.

Putting It Together

Your FAM9B rs5934505 genotype provides insight into one genetic factor that can influence testosterone. Genetics can increase risk but do not determine destiny. Lifestyle, nutrition, sleep, exercise, environment, and medical care all interact with genes to shape hormone levels and fertility. Use your genetic information as a guide to prioritize healthy habits and targeted testing when needed.

Important: PlexusDx provides educational information about genetic predispositions only. This content is not medical advice. Always discuss genetic results, symptoms, and any changes to diet, supplements, or medications with your healthcare provider. Your provider can recommend appropriate laboratory tests and personalized care based on your complete health history.

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 Testosterone and FAM9B rs5934505

What does the FAM9B rs5934505 effect allele mean for testosterone and energy?

The rs5934505 effect allele in the FAM9B gene is associated with lower free and serum testosterone levels. Because testosterone influences energy and mood, some men with the effect allele may be more prone to symptoms such as persistent fatigue, low motivation, and mood changes.

How can I support testosterone and fertility if my rs5934505 genotype shows a genetic predisposition?

Regardless of genotype, evidence-based habits can support healthy testosterone and reproductive health: prioritize high-quality protein and balanced macronutrients, eat zinc- and magnesium-rich foods (e.g., pumpkin seeds, shellfish, spinach, nuts), include healthy fats, do strength training 2 to 4 times per week, and aim for 7 to 9 hours of consistent sleep with morning sunlight exposure. To address potential hormone disruption, reduce unnecessary exposure to endocrine-disrupting plastics and synthetic fragrances when possible.

What lab tests should I ask for if I have symptoms of low testosterone related to FAM9B?

If symptoms persist, ask your healthcare provider about targeted testing, commonly including morning total and free testosterone, SHBG (sex hormone binding globulin), LH, FSH, prolactin, and vitamin D, zinc, and magnesium levels. These labs can help identify treatable causes and guide personalized next steps, including whether supplements like ashwagandha or boron are appropriate.

What tests can help me learn more about Testosterone and FAM9B rs5934505?

The Hormone, Thyroid, and Reproductive Health Genetic Test delivers over 85 personalized genetic insights through a comprehensive Hormone & Fertility Genetic Report, explaining inherited tendencies related to hormonal balance, reproductive function, and endocrine signaling. The Mens Hormone and Fertility Health 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.