Hypothyroidism affects approximately 4 million people in Germany, with women accounting for about 80% of cases. The likelihood of the condition increases significantly after the age of 50. A distinction is made between overt hypothyroidism, i.e., complete thyroid insufficiency, and a latent form, which is far more common and represents a precursor to thyroid hormone deficiency. Iodine is essential for the synthesis of thyroid hormones. The body strives to maintain thyroid hormone supply for as long as possible. In cases of deficiency, this initially triggers a growth stimulus in the thyroid. Prolonged deficiency can lead to autonomous areas (i.e., regions decoupled from the regulatory system, known as “hot nodules”), scarring (“cold nodules”), and, rarely, malignancies.
The most common causes of hypothyroidism include autoimmune diseases (Hashimoto’s thyroiditis), thyroid surgeries, radioiodine treatments, and congenital thyroid defects in children. Hypothyroidism caused by medications, chemotherapy, or other metabolic disorders is significantly rarer.
Symptoms of hypothyroidism may include rapid fatigue, lack of drive, constipation, unintended weight gain, and a depressed mood. Other indicative signs include dry skin, hair loss, cold intolerance, or a slow pulse. In older patients, the condition may develop gradually. In infants, prolonged hypothyroidism can lead to physical and mental developmental impairments.
For family doctors, the patient’s medical history, physical examination findings, and levels of TSH, fT3, and fT4 are crucial. In latent hypothyroidism, TSH levels are elevated, while fT3 and fT4 (the actual thyroid hormones) remain sufficient. At this stage, symptoms may still be mild. In overt hypothyroidism, fT3 and fT4 levels are also reduced. However, the size of the thyroid does not provide reliable information about its functional status.
Therapeutic options include iodide and the thyroid hormone L-thyroxine. The daily iodine requirement for adults in Germany is approximately 200 µg. Iodine deficiency-related thyroid enlargement without significant functional impairment can be treated with 200 µg of iodide per day. According to the DEGAM guideline (German Society for General Medicine), overt hypothyroidism is a clear indication for hormone replacement therapy, while in latent hypothyroidism with TSH levels between 4 and 10 mU/L, treatment should be considered on an individual basis. In contrast, for autoimmune (Hashimoto’s) hypothyroidism, guidelines clearly recommend hormone replacement.
Milk and other foods can reduce the absorption of L-thyroxine. To ensure reliable absorption, the medication should be taken with water at least 30 minutes before breakfast. After initiating replacement therapy, TSH levels should be checked no earlier than eight weeks. Once stable, follow-up checks are recommended every six to twelve months and can be easily performed by the family doctor.