An enlarged thyroid gland is caused by a lack of iodine in the body, and other thyroid system disorders may also result from a lack of thyroid hormones in the body, leading to an enlarged thyroid gland and even other systemic symptoms. In the absence of thyroid hormones, the body may experience symptoms of reduced thyroid function, such as depression, poor appetite, decreased gastrointestinal function, and even normal respiratory movements. Lack of thyroid stimulating hormone in the body may lead to hyperthyroidism, resulting in irritability, increased gastrointestinal function, increased heart rate, and even cardiac disorders, which can lead to atrial fibrillation and ventricular fibrillation, threatening human life. Thyroid system disorders are usually caused by the lack of various trace elements in the body.