The thyroid is made up of small sacs, and this gland is filled with an iodine-rich protein called thyroglobulin along with the thyroid hormones thyroxine (T4) and small amounts of triiodothyronine (T3). The thyroid is situated just below Adam’s apple in the next and had the shape of a butterfly. Regulating one’s metabolism is the primary function of these two hormones, and it does this by controlling the rate at which the body converts oxygen and calories into energy. It is interesting to note that primarily the metabolic rate of every cell in the body is regulated by thyroid hormones. The thyroid gland requires iodine and the amino acid L-tyrosine to make T4 and T3. Therefore a diet which contains too little iodine can limit the amount of T4 the thyroid gland can produce, this may lead to hypothyroidism. When the thyroid gland is visibly enlarged, this is referred to as a goitre. Historically, this condition was most frequently caused by a lack of dietary iodine. However, in countries where salt is iodized, goitre of iodine deficiency is rare.