Light micrograph of hyperplastic goiter. Causes of goiter include Graves's disease, lack of dietary iodine, simple overgrowth or the presence of a tumour. A lack of dietary iodine, which is necessary for the production of thyroid hormones, causes the gland to enlarge in an attempt to increase hormone production. Iodine deficiency was the cause of endemic goiter, formerly common in regions where the diet lacked iodine.