Thyroid diseases. What to know about their causes, symptoms and treatment
The thyroid is a small organ, yet its proper function matters for the whole body. It affects metabolism, heart function, body temperature, the nervous system, fertility and general well-being.
Thyroid diseases are among the most common endocrine disorders. They can involve the amount of hormones produced as well as the structure of the gland itself. Not every change in the thyroid means a hormonal disorder, and not every change requires treatment.
What is the thyroid and what does it do?
The thyroid is an endocrine gland located in the front of the neck, below the larynx. It consists of two lobes joined by an isthmus and is shaped like a butterfly.
Its main task is to produce two hormones:
- thyroxine (T4), the main hormone secreted by the thyroid, which can be converted in tissues into a more biologically active form
- triiodothyronine (T3), which acts on many metabolic processes in the body
Thyroid hormone production is controlled by the pituitary gland, which secretes thyrotropin (TSH). Measuring TSH is usually the first test performed when a thyroid function disorder is suspected.
Thyroid hormones help regulate, among other things:
- the rate of metabolism and energy expenditure
- heart function and the circulatory system
- body temperature
- digestive tract function
- muscle and nervous system function
- lipid and carbohydrate metabolism
- the menstrual cycle and fertility
- growth and nervous system development in children
What are the most common thyroid diseases?
Thyroid diseases can be divided into several main groups.
Thyroid function disorders:
- hypothyroidism (underactive thyroid)
- hyperthyroidism (overactive thyroid)
- subclinical thyroid function disorders
Inflammatory thyroid diseases:
- chronic autoimmune thyroiditis (Hashimoto's disease)
- Graves' disease
- subacute thyroiditis
- postpartum thyroiditis
- other, rarer forms of thyroiditis
Structural changes in the thyroid:
- diffuse goitre
- nodular goitre
- single thyroid nodules
- thyroid cancers
Which thyroid diseases are most common in Poland?
In Poland, hypothyroidism, chronic autoimmune thyroiditis and nodular changes are particularly common.
Their frequency increases with age, and many thyroid diseases are diagnosed more often in women.
In the PolSenior 2 study, which covered the Polish population aged 60 and over, thyroid function disorders were found in about 15.5% of participants. Hypothyroidism was much more common than hyperthyroidism.
These results should not be applied directly to the whole Polish population, because the study concerned older people.
What is hypothyroidism and what symptoms does it cause?
Hypothyroidism is a condition in which the body does not receive enough thyroid hormones.
In populations with adequate iodine intake, the most common cause of primary hypothyroidism is chronic autoimmune thyroiditis, that is, Hashimoto's disease.
Other causes include thyroid surgery, radioiodine treatment, some medications and disturbances of iodine intake. Less often, a deficiency of thyroid hormones results from diseases of the pituitary gland or hypothalamus.
The most common symptoms of hypothyroidism
- chronic fatigue and sleepiness
- increased sensitivity to cold
- dry skin and poorer hair condition
- constipation
- psychomotor slowing
- difficulty concentrating and remembering
- low mood
- weight gain or difficulty maintaining weight
- menstrual disorders
- slowed heart rate
- muscle weakness
Keep in mind that these symptoms are non-specific. Fatigue, hair loss or weight gain alone do not automatically mean hypothyroidism.
Diagnosis requires assessment of hormone tests, primarily TSH and FT4, in the context of the patient's clinical situation.
The basis of treatment for overt hypothyroidism is replacing the missing hormones with levothyroxine.
What is hyperthyroidism and how is it recognised?
Hyperthyroidism occurs when the gland produces excessive amounts of hormones.
In populations with adequate iodine intake, the most common cause of hyperthyroidism is Graves' disease. Hyperthyroidism can also result from autonomously functioning thyroid nodules.
Hyperthyroidism should be distinguished from thyrotoxicosis. Thyrotoxicosis means an excess of thyroid hormones in the body, which can be caused not only by increased production but also by the release of hormones from a damaged gland, for example during thyroiditis.
The most common symptoms of hyperthyroidism
- palpitations and a fast heart rate
- excessive sweating
- intolerance of heat
- hand tremor
- nervousness, irritability and anxiety
- trouble sleeping
- weight loss despite a normal or increased appetite
- more frequent bowel movements
- muscle weakness, especially in the thighs and upper arms
- menstrual disorders
- reduced exercise tolerance
In some patients, especially older ones, symptoms may be less typical and consist mainly of weakness, weight loss or heart rhythm disturbances.
Treatment depends on the cause of hyperthyroidism. It may include antithyroid drugs, radioiodine treatment or surgery.
Why do autoimmune thyroid diseases develop?
Autoimmune diseases develop when immune tolerance is disturbed, that is, when the immune system loses its ability to recognise the body's own tissues and mounts an abnormal response against them.
In the thyroid, the most important autoimmune diseases are Hashimoto's disease and Graves' disease.
How does autoimmunity develop?
The development of an autoimmune disease is a multifactorial process in which both genetic predisposition and environmental factors play a role.
1. Genetic predisposition
Some variants of genes related to the immune system increase susceptibility to autoimmunity. Among others, HLA genes and genes regulating lymphocyte activity are important.
Genetic predisposition alone, however, does not mean that the disease will certainly develop.
2. Environmental factors
In predisposed people, the following may play a role:
- excessive iodine intake
- smoking
- some medications and environmental exposures
- immune changes related to pregnancy and the postpartum period
The role of infections, gut microbiota, chronic stress and other factors is also being studied. For not all of these associations, however, has a direct causal link been shown.
3. Loss of immune tolerance
T and B lymphocytes become abnormally activated and take part in a response directed against thyroid antigens.
4. Development of the autoimmune response
Autoantibodies are produced, and immune cells may accumulate in the thyroid tissue.
The further course depends on the type of disease.
Hashimoto's disease
In Hashimoto's disease there is chronic inflammation of the thyroid, in which the cellular immune response plays an important role and leads to damage of thyroid cells (thyrocytes).
Antibodies against thyroid peroxidase (anti-TPO) and thyroglobulin (anti-Tg) are often present.
As the disease progresses, the thyroid's ability to produce hormones may gradually decrease and hypothyroidism may develop.
Not everyone with Hashimoto's disease will develop hypothyroidism, however. For many years the function of the gland may remain normal.
Important: the presence of antithyroid antibodies does not by itself mean that levothyroxine is needed. The decision to treat depends primarily on thyroid function and the clinical situation.
There is also no need for routine, repeated measurement of anti-TPO levels solely to assess the effectiveness of treatment.
Graves' disease
In Graves' disease the mechanism is different.
The immune system produces antibodies against the TSH receptor (TRAb). Stimulating antibodies activate this receptor, which makes the thyroid produce excessive amounts of hormones.
The disease may be accompanied by thyroid orbitopathy, an autoimmune inflammatory process affecting the tissues of the eye socket.
Symptoms of orbitopathy may include:
- a gritty feeling under the eyelids
- red, watery eyes
- eyelid swelling
- bulging eyes
- double vision
Smoking is one of the most important modifiable risk factors for the occurrence and more severe course of Graves' orbitopathy.
Can diet and lifestyle improve the course of autoimmune thyroid diseases?
This is one of the questions patients ask most often.
Good nutrition, physical activity, sleep and avoiding stimulants matter for general health, immune function and quality of life.
This does not mean, however, that there is a diet that can permanently switch off the autoimmune process or rebuild destroyed thyroid tissue.
Diet
The most rational approach is a varied diet that provides adequate energy, protein, vitamins and minerals.
It makes sense to base the diet on vegetables, fruit, wholegrain cereal products, protein sources and unsaturated fats.
There is not enough evidence that routinely using a gluten-free diet in everyone with Hashimoto's disease improves the course of the disease.
A gluten-free diet is, however, necessary in people with diagnosed coeliac disease, which more often occurs together with autoimmune thyroid diseases.
Physical activity
Regular physical activity improves fitness, metabolic health, sleep quality and well-being.
It has not been shown, however, that exercise alone leads to remission of autoimmune thyroiditis.
In people with uncontrolled hyperthyroidism, especially when it is getting worse, intense exertion may be inadvisable until hormone levels improve.
Sleep and stress
Lack of sleep and chronic stress may adversely affect well-being, metabolism and immune function.
There is no basis, however, for presenting stress as the only cause of Hashimoto's disease or for promising a cure through relaxation techniques.
Looking after sleep and recovery remains a valuable part of a healthy lifestyle, regardless of any thyroid disease.
Can supplements improve thyroid function?
Iodine
Iodine is essential for the synthesis of thyroid hormones. Both deficiency and excessive intake can lead to gland function disorders.
For many years Poland has had a programme to prevent iodine deficiency, which includes iodisation of table salt.
People with autoimmune thyroid diseases should not take high doses of iodine on their own, nor seaweed products containing uncontrolled amounts of it.
Separate recommendations apply to women planning pregnancy, pregnant and breastfeeding women, for whom adequate iodine intake is especially important.
Selenium
Selenium takes part in the metabolism of thyroid hormones and in antioxidant systems.
Studies suggest that selenium supplementation in some people with Hashimoto's disease may lower anti-TPO levels and, in some groups, slightly change TSH levels.
It has not been clearly shown, however, that this translates into lasting improvement in quality of life, prevention of hypothyroidism or the ability to stop levothyroxine.
Therefore routine selenium supplementation in all patients with Hashimoto's disease is not justified.
Excessive selenium intake can be toxic.
Vitamin D
Vitamin D plays a role in regulating immune function.
Observational studies have described deficiency more often in people with autoimmune thyroid diseases, but such an association does not prove that vitamin D deficiency causes the disease.
It is worth ensuring adequate vitamin D intake and correcting deficiency in line with current population recommendations and the individual clinical situation.
There is no basis for using very high doses of vitamin D to treat Hashimoto's disease.
Iron, vitamin B12 and other nutrients
Iron deficiency may affect thyroid hormone synthesis, because thyroid peroxidase is a haem enzyme.
In some patients, especially those with coexisting autoimmune diseases or absorption disorders, deficiencies of vitamin B12 or iron may occur together with thyroid disease.
Testing for and correcting them should be based on history, symptoms and test results, not on the assumption that every patient with Hashimoto's disease needs multi-ingredient supplements.
Most important: supplementation should meet real needs of the body and not replace the diagnosis and treatment of hormonal disorders.
What is goitre and why does it develop?
Goitre is the term for an enlarged thyroid. It does not by itself mean hyperthyroidism or hypothyroidism.
An enlarged thyroid may produce normal, too little or excessive amounts of hormones.
Goitre may develop in the course of iodine deficiency, autoimmune diseases and nodular changes, among other causes.
What symptoms can a goitre cause?
A small goitre often causes no symptoms.
When the thyroid is considerably enlarged, the following may occur:
- visible thickening or asymmetry of the neck
- a feeling of pressure in the neck
- difficulty swallowing
- shortness of breath, especially in certain body positions
- hoarseness or a change in the voice
New shortness of breath, increasing difficulty swallowing or persistent hoarseness require prompt medical assessment.
What is nodular goitre and are thyroid nodules dangerous?
Thyroid nodules are a very common finding, especially in women and older people.
Many are detected by chance during an ultrasound examination of the neck.
Most thyroid nodules are benign and do not require surgery.
Does a thyroid nodule mean cancer?
No. The presence of a nodule is not the same as a diagnosis of thyroid cancer.
The risk of malignancy is assessed mainly from the ultrasound image, and in selected cases a fine-needle aspiration biopsy (FNAB) is performed.
In Europe, the EU-TIRADS classification, among others, is used to assess the ultrasound risk of malignancy.
Not every nodule needs a biopsy. The decision depends on its size, its ultrasound features and additional risk factors.
What symptoms can thyroid nodules cause?
Most nodules cause no symptoms.
Larger lesions may cause a feeling of pressure, discomfort when swallowing or visible asymmetry of the neck.
Some nodules produce hormones independently of control by the pituitary gland. These are called autonomous nodules, and they can lead to hyperthyroidism.
What symptoms may point to thyroid cancer?
Thyroid cancer is a malignant tumour arising from thyroid cells.
The most commonly diagnosed type is papillary carcinoma, which is a differentiated cancer and in most cases has a very good prognosis.
Other types include follicular, medullary and anaplastic carcinoma. They differ in origin, clinical course and treatment.
The most important symptoms of thyroid cancer
In the early stage, thyroid cancer usually causes no symptoms at all.
Signs that call for assessment may include:
- a new, palpable lump in the neck
- a rapidly growing lesion
- persistent hoarseness or a change in the voice
- enlarged lymph nodes in the neck
- difficulty swallowing
- a feeling of pressure or shortness of breath
These symptoms are not characteristic of cancer alone, but they should not be ignored.
How is thyroid cancer diagnosed?
The basic imaging test is ultrasound of the thyroid and regional lymph nodes.
For lesions that meet the relevant criteria, a fine-needle aspiration biopsy is performed and the material obtained is assessed cytologically.
Final diagnosis of some types of cancer requires histopathological examination of tissue removed at surgery.
Treatment depends on the type of cancer, its stage and individual risk. It may include surgery, radioiodine treatment, active surveillance in selected cases and other therapies.
Not every thyroid cancer needs the same management.
When is it worth seeing an endocrinologist?
An endocrinology consultation may be advisable in the case of:
- abnormal TSH or FT4 results
- suspected hypothyroidism or hyperthyroidism
- diagnosed Hashimoto's or Graves' disease
- thyroid nodules that need further assessment
- an enlarged thyroid
- abnormalities on thyroid ultrasound
- symptoms that may point to a hormonal disorder
Keep in mind that a normal TSH level does not rule out all thyroid diseases, especially changes in the structure of the gland.
At the same time, not every abnormal result requires immediate treatment. What matters is the overall clinical assessment.
What to remember about thyroid diseases
Thyroid diseases are common, but they differ in causes, course and treatment.
Hypothyroidism and hyperthyroidism are disorders of hormone production, while goitre and nodules describe changes in the structure of the gland. Autoimmune diseases can lead to hormonal disorders, but this does not always happen.
A healthy lifestyle, good nutrition and correcting deficiencies are important parts of looking after your health. They do not, however, replace proper diagnosis and treatment.
What matters most is not just identifying an abnormality, but understanding its cause and choosing the right management.
This article is for educational purposes and does not replace an individual medical consultation.