Causes of low thyroid hormone levels include autoimmune disease, hyperthyroidism treatment, thyroid surgery, pregnancy and iodine deficiency, according to Mayo Clinic. The incidence of this condition increases with age and is more common in women than men, notes MedicineNet.
Thyroid hormones such as thyroxine are produced by the thyroid gland, an organ located near the base of the neck. These hormones maintain fat and carbohydrate metabolism, regulate protein production and control body temperature. Low levels can result in infertility, heart disease and obesity, stresses Mayo Clinic.
Hashimoto's thyroiditis, an autoimmune disorder, is a common cause of low thyroid hormone levels and occurs when the immune system attacks its own tissues. Treating patients experiencing elevated thyroid hormone levels with anti-thyroid medications or radioactive iodine can also result in low thyroid hormone levels, says Mayo Clinic.
Sometimes, thyroid inflammation may occur during or after pregnancy, lowering thyroid hormone levels. If left untreated, this condition can increase the risks of premature delivery, miscarriage and rise in blood pressure. Additionally, consuming insufficient amounts of iodine can cause hypothyroidism because the body needs this mineral to produce thyroid hormone. Since the body does not produce iodine, patients must get it from food sources such as iodized salt, seaweed, seafood and plants that grow in iodine-rich soil, according to WebMD.