Hashimoto's Thyroiditis: Autoimmunity and the Thyroid

For many patients, a diagnosis of Hashimoto thyroiditis is less about the thyroid than about autoimmunity. They want to know why their immune system is attacking their own gland, whether they can stop it, whether they are at risk of other autoimmune conditions and whether their diet or lifestyle matters. These are reasonable questions, and they have partial answers. This article explains what is known about the autoimmune process, what influences it and where the evidence currently stands on interventions aimed at it.

The autoimmune process

In Hashimoto thyroiditis, immune cells infiltrate the thyroid and gradually destroy thyroid tissue. The process involves T cells, B cells and antibodies against thyroid proteins, principally thyroid peroxidase, an enzyme essential for hormone synthesis, and thyroglobulin, the protein from which hormones are made. Thyroid peroxidase antibodies are present in the great majority of people with the condition and are the main diagnostic marker. The antibodies are markers of the autoimmune process rather than the main cause of damage, which is largely driven by immune cells.

As thyroid tissue is lost, the gland produces less hormone. TSH rises to compensate, and eventually hypothyroidism develops. The gland may enlarge, forming a goitre, or shrink over time.

How common it is

Thyroid peroxidase antibodies are found in a sizeable minority of adults in population surveys, more often in women and increasing with age. Autoimmune thyroid disease is several times more common in women than men. Not everyone with antibodies develops hypothyroidism. In a long term population study in northern England, women with both positive antibodies and a raised TSH had a substantially higher annual risk of developing overt hypothyroidism than women with either finding alone.

Why it develops

Like most autoimmune diseases, Hashimoto thyroiditis arises from an interaction of genetic susceptibility and environmental factors.

The autoimmune cluster

People with Hashimoto thyroiditis have a higher risk of other autoimmune conditions, and vice versa. Commonly associated conditions include coeliac disease, type 1 diabetes, pernicious anaemia and autoimmune gastritis, vitiligo, rheumatoid arthritis, alopecia areata and, rarely, adrenal insufficiency. Practitioners should consider these when symptoms suggest them. Coeliac disease and B12 deficiency deserve particular attention because they are common, treatable and affect levothyroxine absorption and symptoms.

Pregnancy considerations

Thyroid peroxidase antibodies in pregnancy are associated with increased risk of miscarriage and postpartum thyroiditis. A large randomised trial in women with positive antibodies and normal thyroid function who were trying to conceive found that levothyroxine did not increase live birth rates compared with placebo. Women with autoimmune thyroid disease who become pregnant need monitoring of thyroid function because they may not be able to increase hormone production to meet the demands of pregnancy. This care is managed by their obstetric and medical teams.

Can the autoimmune process be modified?

This is the question patients most often ask, and the honest answer is that no intervention has been shown to halt or reverse Hashimoto thyroiditis in the long term. Several have been studied.

Selenium

Meta analyses show that selenium supplementation lowers thyroid peroxidase antibody levels. Whether this reduces progression to hypothyroidism, improves symptoms or improves quality of life has not been established, and excess selenium carries risks, including a possible increase in diabetes risk. Selenium may be reasonable in people with low intake, for a limited period, but it is not a cure.

Gluten free diets

For people with coeliac disease, a gluten free diet is essential. For people without coeliac disease, a small trial found that a gluten free diet reduced antibody levels, but the evidence is limited, and a gluten free diet has costs and nutritional implications. It is not recommended routinely for people without coeliac disease, though some patients choose to try it.

Vitamin D

Low vitamin D is associated with autoimmune thyroiditis, and some trials report reduced antibodies with supplementation. Correcting deficiency is reasonable; evidence for broader benefit is limited.

Other approaches

Myo inositol combined with selenium, low iodine diets, anti inflammatory diets and various supplements have been studied in small trials or not at all. Antibody levels are sometimes used as a target of treatment, but there is no good evidence that tracking or lowering antibodies improves clinical outcomes, and levels fluctuate. Thyroid function and symptoms are more meaningful measures.

Iodine: a balance

People with Hashimoto thyroiditis should have adequate iodine intake, particularly in pregnancy, but should avoid high dose iodine supplements, kelp and large amounts of seaweed, which can worsen thyroid function in susceptible people.

What practitioners can do

1. Explain the condition accurately: it is common, often slowly progressive, treatable with levothyroxine when hypothyroidism develops, and compatible with a normal life.
2. Monitor thyroid function periodically in people with positive antibodies and normal function, as advised by their doctor.
3. Screen for associated conditions when symptoms suggest them, particularly coeliac disease, B12 deficiency and iron deficiency.
4. Optimise nutrition: adequate but not excessive iodine, sufficient selenium from food, correction of vitamin D and iron deficiency.
5. Support general health: sleep, stress management, activity and diet quality affect how people feel, whatever their antibody levels.
6. Discuss interventions honestly, distinguishing established treatment from interventions with limited evidence.
7. Coordinate pregnancy planning with the patient’s doctor.

An illustrative case

A 34 year old woman is found to have positive thyroid peroxidase antibodies and a TSH of 5.2 mU/L with normal free T4. She is anxious, having read that her immune system is destroying her thyroid and that she must follow a strict protocol to stop it. She also has bloating and fatigue.

The practitioner explains the diagnosis, its usual slow course and the evidence about interventions. Her doctor plans to repeat her thyroid tests in a few months and checks for associated conditions. Coeliac serology is negative, but her ferritin and vitamin D are low; both are treated. Her diet, low in fish and dairy and high in processed food, is improved to provide adequate iodine and selenium from food. Her bloating is addressed with dietary changes. She decides against a restrictive protocol. At follow up her TSH is stable, her energy has improved with iron repletion, and her anxiety has eased with an accurate understanding of her condition.

Understanding without overpromising

Hashimoto thyroiditis sits at the meeting point of immunology and endocrinology. Practitioners can help patients most by explaining the autoimmune process honestly, looking for associated conditions and deficiencies, supporting overall health and being clear that, for now, the most reliable treatment is careful monitoring and thyroid hormone replacement when needed.