Hypothyroidism is a chronic disease that occurs due to low levels of thyroid hormone. If hypothyroidism is not treated, long-term complications can cause debilitating disease and even death. In the U.S., autoimmune thyroid disease (Hashimoto’s thyroiditis) is the most common cause of hypothyroidism. However, globally, insufficient iodine intake is the most common cause of hypothyroidism.^[1]

Lack of thyroid hormone can result in various signs and symptoms including the following:^[1]

• Fatigue and weakness
• Intolerance of cold temperature
• Decreased sweating
• Weight gain
• Depression
• Slowed heart rate
• Constipation
• Slowed movement, speech, and thinking
• Dry skin, brittle hair
• Swelling in the face and other body parts
• Goiter (enlarged thyroid)
• Joint and muscle pain
• Irregular menstrual periods and infertility in women

Since signs and symptoms of hypothyroidism are not specific, a health care professional diagnoses it with laboratory values. Most often, thyroid-stimulating hormone (TSH) levels are tested to determine if a patient has hypothyroidism. Also, free thyroxine (T4) levels are tested to determine if the patient has overt or subclinical hypothyroidism. Further testing is usually conducted to determine the cause of the hypothyroidism.^[1]

The most common treatment for hypothyroidism is the drug levothyroxine, which is a synthetic thyroid hormone (T4). To ensure that it is absorbed, levothyroxine should be taken 30-45 minutes before or at least 3 hours after a meal. Many medicines and foods can inhibit the absorption of levothyroxine (especially those containing ions like calcium and iron or substances that reduce acidity in the stomach).To ensure effectiveness, it is important to separate the intake of levothyroxine from these agents.^[1][2]

If hypothyroidism is caused by insufficient iodine intake, an iodine supplement is indicated. Hypothyroidism has been found to occur concurrently with deficiencies in vitamin D, selenium, magnesium, iron, zinc, and vitamin B12, however, it is unclear if supplementation will improve symptoms of hypothyroidism. Black seed has also been studied for hypothyroidism ^[3], while Ashwagandha has been studied for subclinical hypothyroidism.^[4][5]

Dietary iodine intake that is too low or too high can result in hypothyroidism, so it’s important to consume the recommended daily allowance of iodine (150 µg for non-pregnant adults).^[1] Because hypothyroidism precipitates metabolic imbalances, eating a healthy, nutrient-dense diet that promotes a healthy weight is recommended to better manage the condition. Also, there is some speculation that following an anti-inflammatory diet might help reduce autoimmune damage to the thyroid in people with Hashimoto’s thyroiditis.^[4]

Thyroid hormone replacement is effective and the mainstay of hypothyroidism treatment, so other treatments are not typically pursued.^[1] Some early research is looking into whether the thyroid gland can be transplanted to produce adequate hormone replacement.^[6]

The most common cause of hypothyroidism in the U.S. is Hashimoto’s thyroiditis, while in other countries it is iodine deficiency. Certain drugs and therapies can also precipitate hypothyroidism. Some examples include amiodarone, oral tyrosine kinase inhibitors, interferon, bexarotene, rifampin, phenobarbital, phenytoin, carbamazepine, interleukin-2, lithium, radioactive iodine therapy, radiation exposure, and thyroid surgery. Hypothyroidism can also be caused by disorders of the pituitary gland (secondary hypothyroidism) or hypothalamus (tertiary hypothyroidism).^[1]