But, TSH has a second action - it causes growth of thyroid cells. The gland grows and becomes very large under the influence of this high level of TSH secretion. Therefore, most people who live in iodine deficient areas have goitre, thus allowing them to produce enough thyroid hormone for normal body function. Once thyroid hormone levels are restored, TSH secretion stabilizes at a high level. The state of normal thyroid function is called euthyroidism .
All thyroid disorders are much more common in women than in men.
Because of the widespread use of iodized salt and bread, lack of iodine is no longer a cause of thyroid disease in Canada as it was some 50 years ago. Each affects about 1 in 100 of the population. Other less common causes of thyroid disease include nodule, thyroid cancer, subacute thyroiditis and primary hypothyroidism. In this disease, the goitre is due not to TSH but to this unique antibody. The most common cause of this is a cyst or nodule, which may be benign or malignant.