[Cigarette smoking and the thyroid gland].

Relevant English language articles published from 1970 through 1993 regarding the possible influence of cigarette smoking on the thyroid were identified through a MEDLINE search and manual searches of identified reports. Thiocyanate in tobacco smoke influences the thyroid by a competitive inhibition of iodine uptake and organification in the gland. Also, stimulation of the sympathetic nervous system by cigarette smoke and benzpyrene, another constituent of tobacco, is thought to influence thyroid gland function. The thyroid hormones and TSH receptor autoantibodies are not significantly affected by smoking. Smokers have a higher frequency of goitre and increased serum thyroglobulin levels, especially in iodine deficient areas. Graves' ophthalmopathy is strongly associated with cigarette smoking; the more severe the eye disease the stronger the association. Graves' disease without ophthalmopathy is also associated with smoking, though this association is weaker. The thiocyanate level in cord blood equilibrates completely with the level in the mother, and a reverse correlation has been demonstrated between birth weight and thiocyanate level in cord blood. Cigarette smoking induces similar changes in thyroid function in the adult and the fetus. No separate study has elucidated the effects of cessation of smoking. However, there appear to be longstanding effects induced by smoking, some of which are probably irreversible.