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Understanding DIO1 and Thyroid Hormone Conversion

The thyroid gland makes hormones that control metabolism, energy, body temperature, and many aspects of wellbeing. The inactive hormone thyroxine, called T4, must be converted into the active form triiodothyronine, called T3, for tissues to use it. The DIO1 gene encodes the type 1 deiodinase enzyme, which is important for converting T4 to T3, especially in the liver and kidneys. Variations in DIO1 can change how efficiently this conversion happens and may influence energy, weight, mood, and cognitive function.

Why DIO1 matters

  • Type 1 deiodinase removes an iodine atom from T4 to produce T3 and also contributes to balance between T3 and reverse T3, rT3.
  • Lower DIO1 activity can lead to less active T3 and relatively higher rT3, which can cause hypothyroid-like symptoms even if routine tests look normal.
  • The liver and kidneys are key sites for systemic T3 production by DIO1, so overall metabolic health and nutrient status influence enzyme function.

Common symptoms to be aware of

  • Persistent fatigue and low energy
  • Brain fog or difficulty concentrating
  • Slower metabolism or unexplained weight gain
  • Dry skin, cold intolerance, or hair changes
  • Symptoms that do not match standard thyroid lab results

Practical ways to support healthy thyroid hormone conversion

Genetics is one piece of the picture. Diet, nutrients, lifestyle, environmental exposures, and medical conditions all influence thyroid hormone balance. The following strategies can help support optimal conversion of T4 to T3 and general thyroid health.

Diet and nutrients

  • Selenium: Essential for deiodinase enzyme function. Include Brazil nuts (one to two nuts per day is often sufficient), seafood, organ meats, and whole grains.
  • Zinc: Supports thyroid hormone metabolism. Good sources include red meat, poultry, pumpkin seeds, oysters, and legumes.
  • Iodine: Required for thyroid hormone production. Maintain balanced intake through iodized salt, sea vegetables, dairy, and seafood. Avoid excessive iodine unless directed by a clinician.
  • Anti-inflammatory foods: A Mediterranean-style diet rich in colorful fruits, vegetables, nuts, olive oil, and fatty fish provides flavonoids and polyphenols that support overall endocrine health.
  • Avoid highly processed foods and high added sugar intake, which can promote inflammation and metabolic dysregulation.

Supplements to consider with clinician input

  • Selenium supplement at safe, moderate doses if dietary intake is low. Excess selenium can be harmful.
  • Zinc supplement if tested or suspected deficiency, taken with food to reduce nausea.
  • Multivitamin containing iodine only when dietary intake is inadequate or as recommended by your provider.
  • Probiotics and omega 3 fatty acids can support gut and systemic inflammation, which may indirectly affect thyroid function.

Lifestyle and environmental factors

  • Avoid endocrine disruptors such as BPA. Use BPA-free containers, reduce canned food intake, and avoid heating plastics.
  • Regular meal timing and consistent protein intake can support stable metabolism and hormone rhythms. Time-restricted eating may help some people but consult a clinician before major changes.
  • Manage stress with sleep, activity, breathing techniques, and social support. Chronic stress affects hormone balance.
  • Moderate aerobic activity and resistance training support metabolic health and may improve symptoms related to low T3.

Monitoring and testing

If you have symptoms despite normal routine thyroid tests, consider discussing more comprehensive testing with your healthcare provider. Recommended labs to evaluate thyroid hormone conversion include:

  • Free T3
  • Free T4
  • Thyroid stimulating hormone, TSH
  • Reverse T3, rT3

Your clinician can interpret these results in context with symptoms, medications, and other health conditions. Adjustments to diet, supplements, or medical therapy should always be made under professional guidance.

Genetic interpretations for rs11206244 in DIO1

2 effect alleles (TT)

If your genotype is TT for rs11206244, you carry two copies of the effect allele. This is associated with reduced efficiency in converting T4 to T3 via the DIO1 enzyme. You may have higher rT3 and lower free T3 levels, which can produce symptoms such as fatigue, brain fog, cold intolerance, and slower metabolism even when standard thyroid labs like TSH and free T4 appear normal.

Recommendations

  • Prioritize selenium rich foods such as Brazil nuts (one to two per day) and seafood to support deiodinase activity.
  • Include zinc sources like red meat, pumpkin seeds, and legumes to maintain adequate zinc status.
  • Maintain balanced iodine intake through diet rather than high dose supplements unless advised by a clinician.
  • Follow an anti-inflammatory, flavonoid-rich Mediterranean style diet with plenty of vegetables, berries, nuts, and fatty fish.
  • Avoid endocrine disruptors including BPA and phthalates in plastics and personal care products.
  • Consider requesting comprehensive thyroid testing from your healthcare provider: free T3, free T4, TSH, and rT3.
  • Discuss nutrient supplementation with your clinician if dietary intake is insufficient or if tests indicate a deficiency.
1 effect allele (CT)

If your genotype is CT for rs11206244, you carry one copy of the effect allele. This is associated with a moderate reduction in the efficiency of converting T4 to T3. You may experience lower free T3 levels and mild hypothyroid like symptoms, although many people have no noticeable symptoms.

Recommendations

  • Eat selenium rich foods such as Brazil nuts and seafood to support enzyme function.
  • Ensure adequate zinc intake from red meat, poultry, seeds, and legumes.
  • Keep iodine intake balanced through dietary sources and avoid excess supplementation without guidance.
  • Adopt an anti-inflammatory diet higher in fruits, vegetables, whole grains, and healthy fats.
  • Limit exposure to endocrine disrupting chemicals by choosing safer plastics and personal care products.
  • Maintain consistent meal timing and discuss targeted thyroid testing with your healthcare provider if symptoms are present.
0 effect alleles (CC)

If your genotype is CC for rs11206244, you carry two copies of the non effect allele. This is associated with typical DIO1 activity and relatively efficient conversion of T4 to T3 in the liver and kidneys. Your genetic profile suggests your body is generally well equipped to produce active T3 from T4.

Recommendations

  • Continue a nutrient dense diet with selenium rich foods like Brazil nuts and seafood and zinc from red meat and seeds to maintain healthy thyroid function.
  • Keep iodine intake balanced and avoid excessive supplementation unless recommended by a healthcare professional.
  • Follow an anti-inflammatory diet and minimize exposure to endocrine disruptors such as BPA.
  • Monitor energy levels, weight, and any new symptoms and review thyroid labs periodically with your healthcare provider as appropriate.

Final notes and important disclaimer

PlexusDx provides education about genetic predispositions to help you understand potential influences on your health. This information does not constitute medical advice. Always consult your healthcare provider before making changes to your diet, supplements, or medical care. Your clinician can interpret genetic information in the context of your symptoms, medications, lab results, and medical history.