A number of factors can cause your thyroid gland to enlarge. Among the most common are:
Iodine deficiency: Iodine, which is essential for the production of thyroid hormones, is found primarily in seawater and in the soil in coastal areas. The initial iodine deficiency may be made even worse by a diet high in hormone-inhibiting foods, such as cabbage, broccoli and cauliflower.
Although a lack of dietary iodine is the main cause of goiter in many parts of the world, this is not often the case in countries where iodine is routinely added to table salt and other foods
Graves' disease:Goiter can sometimes occur when your thyroid gland produces too much thyroid hormone (hyperthyroidism)
Hashimoto's disease:Goiter can also result from an underactive thyroid (hypothyroidism). Like Graves' disease, Hashimoto's disease is an autoimmune disorder. But instead of causing your thyroid to produce too much hormone, Hashimoto's damages your thyroid so that it produces too little.
Sensing a low hormone level, your pituitary gland produces more TSH to stimulate the thyroid, which then causes the gland to enlarge.
Thyroid cancer:Thyroid cancer is far less common than benign thyroid nodules. Cancer of the thyroid often appears as an enlargement on one side of the thyroid.
Multinodular goiterIn this condition, several solid or fluid-filled lumps called nodules develop in both sides of your thyroid, resulting in overall enlargement of the gland.
Solitary thyroid nodules:In this case, a single nodule develops in one part of your thyroid gland. Most nodules are noncancerous (benign) and don't lead to cancer
Pregnancy:A hormone produced during pregnancy, human chorionic gonadotropin (HCG), may cause your thyroid gland to enlarge slightly
Inflammation: Thyroiditis is an inflammatory condition that can cause pain and swelling in the thyroid. It may also cause an over- or underproduction of thyroxin.
Less common causes of goiter include the following:
Nodules - benign lumps, single or multiple
Smoking - thiocyanate in tobacco smoke interferes with iodine consumption
Hormonal changes - pregnancy, puberty and the menopause can affect the thyroid
Thyroiditis - inflammation caused by infection, for example
Lithium - the psychiatric drug can interfere with thyroid function
Overconsumption of iodine - too much iodine can cause goiter, just as too little does