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Understanding Your FAM9B Result and What It Means for Testosterone

Testosterone is a central hormone for muscle mass, energy, libido, bone density, mood, and overall hormonal balance in men and women. Variations in the FAM9B gene, located on the X chromosome, have been linked to differences in testosterone production. Some FAM9B variants are associated with lower average total and free testosterone levels. While the genetic effect tends to be stronger in men, women with these variants may also notice subtle shifts in their hormone balance.

How FAM9B Can Influence Hormone Health

The FAM9B gene influences testicular testosterone production and neuroendocrine control of androgen balance. Depending on which alleles you carry, your baseline setpoint for circulating testosterone may be typical, intermediate, or lower than average. Lower baseline testosterone can contribute to reduced muscle mass, lower energy, decreased libido, changes in metabolic health, and lower bone density over time.

What You Can Do to Support Healthy Testosterone

Genetics is one piece of the puzzle. Lifestyle, nutrition, sleep, stress, and environmental exposures all influence hormone levels and how you feel. The following practical steps support healthy testosterone production and overall endocrine balance.

  • Nutrition
    • Eat a balanced diet with adequate protein to support muscle repair and hormone synthesis.
    • Include healthy fats from sources like olive oil, avocados, nuts, seeds, fatty fish, and eggs. Dietary fat supports steroid hormone production.
    • Focus on zinc rich foods: oysters, red meat, poultry, pumpkin seeds, and legumes. Zinc plays a direct role in testosterone production.
    • Prioritize magnesium from leafy greens, nuts, seeds, whole grains, and beans. Magnesium helps support sleep and hormone balance.
    • Ensure adequate vitamin D through safe sun exposure and vitamin D rich foods like fatty fish, fortified dairy or consider supplementation if levels are low.
    • Include boron containing foods like nuts, legumes, and dried fruit. Small amounts of boron may support normal testosterone metabolism.
  • Supplements to Consider
    • Vitamin D3 if blood levels are low. Work with your healthcare provider to test and dose appropriately.
    • Zinc and magnesium supplementation when dietary intake is inadequate. Avoid high dose zinc long term without monitoring.
    • Boron in low supplemental amounts may be helpful for some people. Use guidance from a clinician on dosing.
    • A multivitamin that covers basic micronutrients can be useful if your diet is inconsistent.
  • Exercise
    • Prioritize regular resistance training to stimulate muscle growth and support testosterone production.
    • Include higher intensity interval sessions periodically. Avoid excessive endurance training without adequate recovery.
  • Sleep and Recovery
    • Aim for 7 to 9 hours of quality sleep per night. Poor sleep can significantly lower testosterone.
    • Establish consistent sleep timing and good sleep hygiene.
  • Stress Management
    • Chronic stress raises cortisol which can suppress testosterone. Use breathing exercises, meditation, therapy, or hobbies to manage stress.
    • Prioritize social connection and activities that restore you mentally and physically.
  • Reduce Exposure to Endocrine Disruptors
    • Limit contact with BPA, certain phthalates, and other hormone-disrupting chemicals by choosing glass or stainless steel for food storage, avoiding microwaving plastics, and reducing use of fragranced personal care products.
  • Regular Monitoring
    • If you have symptoms suggestive of low testosterone, discuss testing with your healthcare provider. Useful labs include total testosterone, free testosterone, sex hormone binding globulin (SHBG), luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol, and vitamin D.
    • Repeat testing in the morning when testosterone is typically highest and consider follow up measurements to track changes over time.

Genetic Interpretation

2 effect alleles — TT genotype

If you have the TT genotype for rs5934505, which means you carry two copies of the effect allele, your genotype is associated with the lowest average total and free testosterone levels compared to other genotypes at this location. The FAM9B variant may contribute to a lower baseline testosterone setpoint. Possible clinical features over time include reduced muscle mass, lower energy, diminished libido, and lower bone density. Proactive strategies are valuable: prioritize resistance training, optimize sleep, manage chronic stress, and ensure adequate intake of zinc, magnesium, vitamin D, and boron. Regular hormone monitoring and discussion with your healthcare provider can help determine whether any targeted interventions are needed.

1 effect allele — CT genotype

If you have the CT genotype for rs5934505, which means you carry one copy of the effect allele, you are likely to have lower free testosterone on average than individuals without the T allele but higher than those with two T alleles. This intermediate position may predispose you to modest reductions in muscle mass, energy, libido, or metabolic shifts if testosterone declines. Supporting healthy testosterone through resistance exercise, adequate sleep, stress reduction, and ensuring sufficient zinc, magnesium, vitamin D, and boron intake can help maintain function and reduce the chance of symptomatic hormone deficiency. Consider periodic hormone checks if symptoms develop.

0 effect alleles — CC genotype

If you have the CC genotype for rs5934505, which means you carry two copies of the non-effect allele, your genetic result at this location does not include the T allele that is associated with lower testosterone. Your FAM9B variant corresponds to typical or higher testosterone production capacity compared to T allele carriers. While your genetic predisposition supports normal testicular testosterone production and androgen balance, lifestyle factors still strongly influence hormone health. Continue regular resistance training, get adequate sleep, manage stress, and maintain good intake of zinc, magnesium, vitamin D, and boron to support natural hormone production.

When to Talk with a Healthcare Provider

  • Consider evaluation if you have persistent symptoms such as low libido, reduced muscle mass or strength, unexplained fatigue, or recurrent low mood.
  • Bring your genetic result to the conversation so your clinician can interpret it alongside symptoms, physical exam, and laboratory data.
  • Do not start prescription hormone therapies based on genetic results alone. Treatment decisions should follow clinical assessment and appropriate testing.

PlexusDx does not provide medical advice. This information is educational and genetic predispositions do not guarantee a medical outcome. Always consult with your healthcare provider before making changes to medication, supplements, or treatment plans, or to interpret lab results in context of your personal health history.