Both hypo and hyperthyroidism are a result of a disease in caused by malfunction of the thyroid gland located in the neck as represented by the image below left. The causes of chronic hypothyroidism are fairly distinct. Around the world in third-world and developing countries, iodine deficiency is the most common cause of hypothyroidism. This used to be true as well for developed countries, but today this is a less common cause as iodine usually finds its way into our diets without too much trouble. In modern-day developed countries, hypothyroidism is mainly a result of Hashimoto's thyroiditis, a birth defect which lacks a thyroid gland or a deficiency of hormones from either the hypothalamus or the pituitary gland. Hypothyroidism can also be a result of postpartum thyroiditis. This is a condition which affects about 5% of all women within a year after child-birth. The first phase is typically hyperthyroidism the causes of which will later be examined. Then, the thyroid will either return to normal or the woman will develop hypothyroidism. Of those women who undergo hypothyroidism connected with postpartum thyroiditis, one in five will develop life-long hypothyroidism involving treatment for the rest of their lives. Hypothyroidism can also be an outcome of inheritance. Hyperthyroidism is the consequence of excessive thyroid hormone production, causing an overactive height growth and increased pace of all the body's organs and intestines. Thyroid hormone usually controls the speed of each the processes in the digestive system. This rate is called one's metabolism. Hyperthyroidism in humans is mainly caused by Graves' disease (caused by an antibody-mediated auto-immune reaction), toxic multinodular goitre (where there is excess production of thyroid hormones), and toxic thyroid adenoma. Excess thyroid hormones from drugs/pills also have the potential to cause hyperthyroidism.
Hypothyroidism is a disease caused by inadequate production of