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Phenylalanine Benefits For Thyroid Health

Find out if supplementing the amino acid phenylalanine is necessary for thyroid health.
Phenylalanine Benefits For Thyroid Health
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Phenylalanine is an essential amino acid in our bodies that helps make thyroid hormones. However, we cannot make phenylalanine ourselves; it must come from our diet. Some people take phenylalanine as a dietary supplement to help treat certain health conditions. Still, there is not much evidence to confirm that phenylalanine can treat health conditions. Nonetheless, our bodies need it (in most cases), so let's uncover who can benefit from phenylalanine and why it may help with thyroid health.

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What does phenylalanine do?


As an amino acid, phenylalanine is a building block to other proteins in the body. Primarily, it gets converted to tyrosine, which helps to make adrenal hormones like dopamine, norepinephrine, and epinephrine. It also helps produce thyroid hormones. 


Because of its role in creating neurotransmitters, most research on using this amino acid as treatment has concentrated around mood disorders like depression. Indeed, through a separate pathway, phenylalanine is converted to phenylethylamine, which may help elevate your mood.


Aside from boosting your mood, phenylalanine may also help with:

  • Skin conditions like rosacea and acne
  • Chronic pain
  • Vitiligo 
  • Substance abuse 
  • Parkinson's disease
  • Osteoarthritis
  • Rheumatoid arthritis
  • ADHD


There are three forms of phenylalanine: L-phenylalanine, D-phenylalanine, and DL-phenylalanine. L-phenylalanine is the active form that is found in foods and helps make proteins and other molecules. 


What does phenylalanine have to do with the thyroid?


Tyrosine is an amino acid that is a precursor to thyroid hormones. The following steps are how thyroid hormones are produced:


  1. The thyroid gland needs iodine from your diet to oxidize into thyroid peroxidase (TPO), which makes the iodine active. 
  2. Next, active iodine molecules can attach to tyrosine, which is found in thyroglobulin. 
  3. When iodine and tyrosine join, they create the precursors to thyroid hormones: monoiodotyrosine (T1) and diiodotyrosine (T2). 
  4. T1 and T2 then combine to form triiodothyronine (T3) and thyroxine (T4).
  5. At this point, you may recognize that T3 and T4 are the primary thyroid hormones that our body uses to help regulate metabolic processes throughout the body. These are two of the primary thyroid hormone levels assessed in a complete thyroid panel.


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How phenylalanine might benefit patients with a thyroid condition


People with an underactive thyroid gland may benefit from supplemental phenylalanine because it may increase tyrosine and, consequently, thyroid hormone production. Aside from boosting thyroid hormones, phenylalanine may also improve your stress response in stressful situations, which we know can be problematic in hypothyroidism and Hashimoto's disease.


However, there is little research to support taking a phenylalanine supplement if you have a thyroid condition. Instead, many patients with hypothyroidism take a supplement that contains L-tyrosine, as that is the more direct way to help support your thyroid hormone production.


Because of tyrosine's role in producing "feel good" neurotransmitters, you may experience an improvement in your mood, lower stress levels, and counter adrenal depletion that can occur in thyroid conditions.


People with an overactive thyroid (hyperthyroidism) will want to avoid supplementing with phenylalanine, as it may increase thyroid hormone levels, which are already too high in this condition.

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Where can you find phenylalanine?


Primarily, we get phenylalanine from our food. Usually, it is in protein-rich foods like:

  • Eggs
  • Dairy products
  • Red meat
  • Poultry
  • Fish
  • Legumes (beans and peanuts)
  • Sunflower and sesame seeds


You can also take a supplement that contains L-phenylalanine. However, its effectiveness and safety are still up for further research. 


Some people also use it directly on their skin, as it may help treat vitiligo when applied topically. 


Who should not take phenylalanine?


We know that the amino acid phenylalanine plays a role in creating chemical messengers in our bodies. However, the extent to which we should supplement it outside of our diet, if at all, is unclear. 


People with phenylketonuria (PKU) should not take phenylalanine. PKU is a rare genetic disorder that prevents the body from breaking down the amino acid phenylalanine. If you have PKU and eat foods that contain phenylalanine (including artificial sweeteners with aspartame), phenylalanine builds up in the blood, which can damage the nervous system and brain, causing a number of health problems like seizures, psychiatric problems, or intellectual disability.


To rule out this genetic condition, babies in the United States go through a PKU screening test within the first few days of life. If a baby is diagnosed with this rare condition, following a diet that avoids phenylalanine-rich foods can help prevent lifelong complications.


Learn how to optimize your thyroid health by starting with an at-home thyroid blood test kit to assess your thyroid function. Then follow up with a thyroid doctor to ensure you are on the best path toward living well. 


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Julia Walker, RN, BSN

Clinical Nurse

Julia Walker, RN, BSN, is a clinical nurse specializing in helping patients with thyroid disorders. She holds a Bachelor of Science in Nursing from Regis University in Denver and a Bachelor of Arts in the History of Medicine from the University of Colorado-Boulder. She believes managing chronic illnesses requires a balance of medical interventions and lifestyle adjustments. Her background includes caring for patients in women’s health, critical care, pediatrics, allergy, and immunology.

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