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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.