Low levels of thyroid hormone can cause symptoms that include increased cold sensitivity, constipation, brittle hair and nails, fatigue and depression, according to Healthline. Other symptoms include menstrual abnormalities, hoarseness, thickening of the skin, slow speech and a decreased sense of taste and smell.
A decreased level of thyroid hormone is commonly known as hypothyroidism, explains Mayo Clinic. The condition is caused by an underproduction of certain hormones by the thyroid gland, which results in a disturbance of normal chemical reactions in the body. Common causes of hypothyroidism include autoimmune disease, treatment of hyperthyroidism, thyroid surgery, radiation therapy and certain medications. Other causes include pregnancy, pituitary disorders, congenital disorders and iodine deficiency.
Risk factors include women who are older than 60 years, a family history of autoimmune disease and recent pregnancy, states Mayo Clinic. When left untreated, the disorder can lead to complications that include the development of a goiter, heart problems, peripheral neuropathy, myxedema, infertility and mental health problems. Babies who are born to mothers with untreated thyroid disease have an increased risk of birth defects, which include developmental and intellectual problems. Most people with hypothyroidism require lifetime treatment with oral levothyroxine, a synthetic thyroid hormone. Patients typically notice an improvement of symptoms within the first two weeks of therapy.