THYROID RULES ALL
- Kirstin Bruges Homeopath
- 5 days ago
- 5 min read
Thyroid and MCAS: Thyroid, Mast Cells, Gut and Immune System Interlink
Do you experience fatigue, brain fog, temperature sensitivity, palpitations, digestive problems, flushing or reactions to foods—and wonder whether your thyroid or mast cells are responsible?
Thyroid disorders and mast cell activation syndrome (MCAS) can produce overlapping symptoms. They may also interact through the immune system, inflammatory signalling, thyroid-hormone metabolism and the gut.
Two Important Thyroid Patterns
When looking at persistent thyroid symptoms, two patterns deserve particular attention.
1. Autoimmune thyroid disease
With autoimmune thyroid disease, the immune system mistakenly targets the thyroid.
In Hashimoto’s thyroiditis, inflammation gradually damages the thyroid and commonly leads to an underactive thyroid. In Graves’ disease, antibodies stimulate the thyroid, causing excessive thyroid-hormone production.
In both cases, the thyroid is affected by wider immune-system dysregulation. The thyroid gland cannot therefore be viewed entirely in isolation.
2. Reduced conversion of T4 into T3
The thyroid produces mainly thyroxine, known as T4. T4 acts partly as a circulating reserve and must be converted into the more active hormone T3 within tissues throughout the body.
The liver plays an important role in this conversion, but T4-to-T3 conversion also occurs in the kidneys, muscles, brain and other tissues.
During serious illness, inflammation, prolonged calorie restriction or substantial physical stress, circulating T3 can temporarily fall. This is sometimes called non-thyroidal illness syndrome or “low T3 syndrome.” It does not automatically mean that the thyroid gland itself has failed.
The thyroid may be trying to function while the wider body is struggling to use or regulate its hormones effectively.
What Are Mast Cells?
Mast cells are immune cells found throughout the body, particularly within the skin, digestive tract, respiratory tract and tissues surrounding nerves and blood vessels.
When activated, mast cells release chemical messengers, including:
Histamine
Prostaglandins
Leukotrienes
Tryptase
Cytokines and chemokines
This is normally a protective response to infection, injury or allergens. Problems can arise when mast cells become overly sensitive or release their mediators inappropriately.
MCAS may cause recurrent symptoms affecting several body systems, including flushing, itching, hives, abdominal pain, diarrhoea, headaches, dizziness, rapid heartbeat, nasal congestion and sensitivity to foods, alcohol, heat, medication or hormonal changes.
The Thyroid–Mast Cell Connection
As Dr Becky Campbell discusses in her article on thyroid health and mast cells, the relationship may potentially work in both directions.
Mast cells are not simply containers for histamine. They communicate with the immune, nervous and hormonal systems. Research suggests they may respond to thyroid hormones, convert T4 into T3 locally and store small amounts of thyroid hormone.
Studies have also explored whether thyroid antibodies can interact with receptors on mast cells. This may offer one possible explanation for why some people with autoimmune thyroid disease experience symptoms resembling mast-cell activation.
However, having Hashimoto’s, Graves’ disease or thyroid antibodies does not automatically mean that someone has MCAS. Much of the research into the direct relationship remains experimental, and the mechanisms have not been fully established in human clinical studies.
Mast-cell mediators may also influence inflammatory and hormonal signalling. Inflammation can affect the way thyroid hormones are produced, transported and converted within the body.
This creates a possible feedback pattern:
Autoimmune thyroid activity → altered immune signalling → greater mast-cell sensitivity → increased inflammatory mediators → further disturbance of thyroid-hormone metabolism.
This remains a developing area of research rather than a proven explanation for every case.
Why the Symptoms Can Be Confusing
Thyroid dysfunction and mast-cell activation can share a surprising number of symptoms:
Fatigue and reduced stamina
Brain fog and poor concentration
Anxiety or internal restlessness
Palpitations
Heat or cold intolerance
Headaches
Digestive disturbance
Sleep problems
Muscle weakness
Menstrual or hormonal changes
Altered appetite or weight
Skin sensitivity
The Gut–Immune–Thyroid Connection
The gut does not simply “make T3,” but it plays several important supporting roles.
The digestive system is involved in the absorption of iodine, iron, selenium, zinc, amino acids and thyroid medication. Gastrointestinal inflammation or malabsorption can therefore complicate thyroid management.
Coeliac disease is particularly relevant because it occurs more frequently alongside autoimmune thyroid disease. Untreated coeliac disease can also reduce the absorption of levothyroxine.
An underactive thyroid may slow intestinal movement, contributing to constipation and possibly increasing susceptibility to small intestinal bacterial overgrowth, or SIBO. Changes in the gut microbiome may then affect immune regulation and histamine handling.
Diamine oxidase—or DAO—is one of the enzymes involved in breaking down histamine within the digestive tract. If histamine intake and mast-cell release exceed the body’s ability to process it, symptoms may become more noticeable.
Low DAO activity is sometimes discussed in relation to histamine intolerance, but histamine intolerance and MCAS are not the same condition. DAO testing or supplements cannot diagnose MCAS.
Do You Know the Hidden Thyroid Stressors?
Autoimmunity
Coeliac disease and malabsorption
Too little—or too much—iodine
Iodine is essential for thyroid-hormone production, but excess iodine can aggravate thyroid dysfunction in susceptible individuals. High-dose iodine should not be taken casually, especially with autoimmune thyroid disease.
Nutritional deficiencies
Iron, selenium and zinc contribute to normal thyroid physiology. Deficiencies should be identified and corrected appropriately, but high-dose supplementation is not automatically beneficial and can be harmful.
Illness, inflammation and under-eating
Acute illness, persistent inflammation, prolonged fasting and inadequate calorie intake can lower circulating T3.
Medication and supplement interactions
Calcium, iron, antacids and certain foods can reduce levothyroxine absorption when taken too close to it. Biotin supplements can interfere with some thyroid blood tests and produce misleading results.
Stress and poor sleep
Hormonal fluctuations
Individual mast-cell triggers
Looking at the Whole Pattern
The thyroid, immune system, mast cells, gut, liver, nutritional status and reproductive hormones continually communicate. A disturbance in one area may influence how another system functions or how symptoms are experienced.
At the same time, it is important not to assume that every persistent symptom is caused by MCAS or poor T4-to-T3 conversion. Anaemia, coeliac disease, infection, medication effects, nutritional deficiencies, dysautonomia and other hormonal conditions can produce similar symptoms.
In my homeopathic practice, I look at the complete pattern: the person’s medical diagnoses, individual symptoms, sensitivities, digestion, hormonal changes, energy, sleep and responses to environmental or emotional stressors.
Understanding the connections can help us ask better questions—and see the whole person rather than treating every symptom as an isolated event.
This article is for educational purposes and is not a substitute for individual medical diagnosis or treatment.
Further Reading
For more information on how homeopathy can support you returning to a state of balance and repair. Do get in touch via my website or email kirstin.bruges@hotmail.com
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