The most common disorders of the thyroid gland are hyperthyroidism and hypothyroidism. Hyperthyroidism is a condition in which the thyroid gland secretes too much thyroid hormone, and hypothyroidism results in insufficient amounts of thyroid hormone. Both hyperthyroidism and hypothyroidism have been linked to cell damage. The sleep-regulating hormone melatonin can protect against cell damage. However, it may also down-regulate the activity of the thyroid gland. So melatonin could worsen hypothyroidism.
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You need oxygen to turn the components of food into energy that your body can use. Though this metabolic process is essential to staying alive, it also produces toxic and unstable byproducts called free radicals. Free radicals are produced when electrons are removed from an atom or molecule. Free radicals take in electrons from other cell molecules. This can lead to cell damage and abnormalities in cell growth, a condition called oxidative stress. Antioxidants, such as selenium, beta-carotene and vitamins C and E, can help prevent cell damage by giving an electron to free radicals.
Hyperthyroidism, or overactive thyroid, is most commonly a result of an autoimmune disease, a condition in which your immune system attacks the thyroid gland. Occasionally, hyperthyroidism can result from a non-cancerous tumor in the thyroid gland or an infection of the thyroid gland. Hyperthyroidism results in an increased secretion of the thyroid hormones T3 and T4. Excess thyroid hormones in the bloodstream lead to an increased metabolic rate. As a higher metabolism requires higher amounts of oxygen to produce the needed energy, hyperthyroidism can result in oxidative stress.
Hypothyroidism, or underactive thyroid, is most often an autoimmune condition or the result of treating hyperthyroidism by removing the thyroid gland or treating it with radioactive idodine. When the thyroid gland is underactive, smaller amounts of the thyroid hormones T3 and T4 are secreted into the bloodstream, decreasing your metabolism. Whether hypothyroidism leads to oxidative stress is unclear. A study published in the November 2010 issue of "Clinical Chemistry and Laboratory Medicine” found that hypothyroidism is correlated with increased levels of low-density lipoprotein, or bad cholesterol, which can lead to oxidative stress. Thus hypothyroidism may be an indirect source of oxidative stress.
Melatonin is derived from the mood-enhancing neurotransmitter serotonin in the pineal gland. It regulates your 24-hour sleep rhythm and is commonly used to prevent jet lag, to cure sleep disorders and to adjust the sleep rhythm in people who work nightshifts. Melatonin is also a potent antioxidant and can be used to prevent oxidative stress. According to a review published in the April 2002 issue of “Neuro Endocrinology Letters,” however, melatonin may down-regulate the activity of the thyroid gland. So melatonin may be beneficial as a supplement for individuals with hyperthyroidism, but taking a melatonin supplement with hypothyroidism could worsen the condition.