The thyroid is a butterfly-shaped endocrine gland located just below the Adams apple, and primarily makes hormones involved in metabolic rate and protein synthesis.
The thyroid secretes hormones tri-iodothyronin (T3) and thyroxine (T4) (which are created from iodine and tyrosine), and the peptide hormone, calcitonin. The hypothalamus gland produces thyrotropin-releasing hormone (TRH) which in turn regulates the anterior pituitary gland, which then secretes thyroid stimulating hormone (TSH) which controls the hormonal output from the thyroid. TSH secretion increases thyroidal uptake of iodine, and stimulates the synthesis and release of T3 and T4 (1). In the absence of sufficient iodine, TSH levels remain elevated, leading to goitre, an enlargement of the thyroid gland that reflects the body’s attempt to trap more iodine from the circulating blood and produce thyroid hormones. The thyroid gland is responsible for:
Metabolism - Hormone secretion affects the metabolic rate through appetite, nutrient absorption, gut motility,and breakdown of glucose and fats.
Cardiovascular function - Hormones can affect the rate of breathing and oxygen consumption, hence influencing blood flow in the body and body temperature.
Development - Neurological development is the main function of thyroid hormones in children, along with regulating growth rate.
Hyperthyroidism is when excess amounts of thyroid hormones are secreted in diseases such as Graves’disease, or by certain drugs such as amiodarone that create an excess of iodine (1). Symptoms may include weight loss,insomnia, tremors, increased appetite, heart palpitations, anxiety and nervousness. Treatments include medications to suppress thyroid function, or radioactive iodine to destroy the thyroid tissues.
Hypothyroidism is an under active thyroid gland, with typical symptoms of abnormal weight gain, tiredness, heavy menstrual bleeding, constipation, cold intolerance, reduced heart rate, and hair loss. Inadequate amounts of thyroid hormones are secreted, most commonly due to iodine deficiency, which can lead to goitre. Hypothyroidism is managed with thyroxine replacement.
Goitre is an enlargement of the thyroid gland, and it has many causes. It can be due to hyperplasia of the thyroid to compensate for decreased efficacy, usually due to iodine deficiency, or the thyroid gland may be producing too much T3 and T4 (as in Graves’ disease) (2,3). Treatment for goitre can be small doses of ingested iodide, or radioactive iodine is given to shrink the goitres, and in some cases surgery maybe required.
How much Iodine do we need?
RDA of iodine for healthy males and females is 150 mcg daily, or 220 mcg in pregnancy and lactation. Upper tolerable limit set by IOM is 1100 ug/day (4). People consuming moderate amounts of seafood, dairy products and meat or regularly taking iodine-containing vitamin/ mineral preparations are unlikely to become deficient (1). Seafood is rich in iodine, as are plants living in coastal areas. Dairy is also a good source of iodine, passed on from fortified cow feed or aerial sprays on grasses (5). Vegans who do not eat seafood or dairy may beat risk of iodine deficiency, as the plants consumed even if grown in coastal areas maybe deficient in iodine (5). Iodized salt is usually recommend as in 5 g (1 tsp) contains about 50 mcg iodine (1).
Check out feedspot for more great nutrition blogs. Please leave a comment and share also.