Thyroid Peroxidase Antibodies

Thyroid peroxidase (TPO) is an enzyme produced by the thyroid gland, a small organ at the base of your neck that controls metabolism, energy production, and growth. TPO’s main job is to help create the thyroid hormones thyroxine (T4) and triiodothyronine (T3) by attaching iodine to the amino acid tyrosine. These hormones regulate nearly every system in the body — from heart rate and temperature to digestion and brain function.

In some people, the immune system mistakenly identifies this vital enzyme as harmful and begins producing antibodies against TPO. These antibodies (TPOAb) attach to and damage thyroid cells, setting off autoimmune thyroid disease (AITD). The two main conditions linked with TPOAb are Hashimoto’s thyroiditis, which causes an underactive thyroid (hypothyroidism), and Graves’ disease, which causes an overactive thyroid (hyperthyroidism).

Because TPOAb can be detected in the blood years before symptoms appear, testing provides valuable insight into early autoimmune activity — even in people whose standard thyroid hormones (TSH, T3, T4) still appear normal. Elevated levels signal that the immune system is attacking thyroid tissue, increasing the risk of progressive thyroid dysfunction.

Thyroid peroxidase antibodies are among the most clinically relevant immune markers for thyroid health because they reveal whether the immune system — not the gland itself — is driving thyroid changes.

High TPOAb are a hallmark of Hashimoto’s thyroiditis, the most common cause of hypothyroidism worldwide. In this condition, persistent antibody activity gradually destroys thyroid cells, reducing hormone output. Symptoms often include fatigue, dry skin, sensitivity to cold, hair thinning, brain fog, and weight gain. Even when thyroid hormone levels remain normal, people with positive TPOAb have a much higher lifetime risk of developing overt hypothyroidism, especially women and older adults.

In Graves’ disease, another autoimmune condition, TPOAb may coexist with antibodies that overstimulate the thyroid, leading to excessive hormone production. This results in symptoms such as anxiety, rapid heartbeat, tremors, and heat intolerance.

Beyond thyroid disorders, positive TPOAb can occur in other autoimmune diseases (e.g., type 1 diabetes, celiac disease, or rheumatoid arthritis), reflecting a broader tendency toward immune dysregulation. In pregnant women, elevated TPOAb are linked with a higher risk of postpartum thyroiditis and temporary hypothyroidism after birth.

Dietary Factors
Iodine is essential for thyroid hormone synthesis, yet both deficiency and excess can trigger autoimmune activity. Seafood, eggs, and iodized salt provide iodine in moderate, balanced amounts, whereas excessive intake (e.g., seaweed snacks or iodine-rich supplements) can overstimulate antibody production. Selenium, abundant in Brazil nuts, tuna, and eggs, helps protect thyroid cells from oxidative stress and may reduce antibody levels. Vitamin D, found in fatty fish and through sunlight exposure, modulates immune balance and is often low in those with autoimmune thyroid disease.

Lifestyle Factors
Chronic stress and inadequate sleep disrupt immune tolerance, increasing inflammation and cortisol levels, which can worsen thyroid autoimmunity. Regular moderate exercise, mindfulness, and restorative sleep promote immune equilibrium and healthier hormone metabolism.

Related Biomarkers

• TSH (thyroid-stimulating hormone) – Often rises as the thyroid becomes underactive in Hashimoto’s.

• Thyroglobulin Antibodies (TgAb) – Frequently elevated alongside TPOAb in autoimmune thyroiditis.

• Free T3 and Free T4 – Reflect how well the thyroid is still producing and converting hormones.
  

Micronutrient Impacts
Deficiencies in selenium, zinc, iron, and vitamin D are linked to higher autoimmune activity. Iron supports the TPO enzyme itself, while zinc assists T3 conversion and immune function.

Environmental Influences
Exposure to endocrine-disrupting chemicals (EDCs) —s uch as BPA in plastics, phthalates in cosmetics, and certain pesticides — can mimic or block thyroid hormones, altering immune tolerance. Reducing these exposures (e.g., using glass bottles, choosing fragrance-free products) can support thyroid and immune balance.

If Your Results Are High

If your TPOAb levels are high, this suggests immune-related thyroid inflammation.

• Diet:

  • Include selenium-rich foods (Brazil nuts 1–2 daily, sardines, eggs) and ensure adequate but not excessive iodine (seafood 2–3 times weekly, avoid kelp supplements).

  • Prioritise vitamin D from sunlight or oily fish.

  • Limit ultra-processed foods that drive inflammation.
    .

• Lifestyle:

  • Focus on stress-management strategies such as yoga, meditation, or walking outdoors.

  • Prioritise 7–9 hours of restorative sleep.

  • Avoid smoking and minimise exposure to environmental toxins.
    .

• Supplements: Selenium (100–200 µg/day) and vitamin D (if deficient) may help reduce antibody levels — only under professional supervision.
  

If Your Results Are Low

Low TPOAb levels generally indicate no active autoimmune process.

• Diet: Maintain balanced intake of iodine and selenium through whole foods.
  

• Lifestyle: Continue regular physical activity, stress management, and consistent sleep.
  

• Supplements: None specifically required unless nutrient deficiencies are confirmed.

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5. Adam LN, Abbas AM. Thyroid Peroxidase Gene Variants and Autoimmunity in Subclinical Hypothyroidism: Molecular Mechanisms and Clinical Implications.Mol Biol Rep. 2025;52(1):1049. doi:10.1007/s11033-025-11174-y