Cigarette smoking and the thyroid

Cigarette smoking alters a variety of endocrine systems including thyroid hormones. If in healthy adults, studies have shown that tobacco has little effect on thyroid function, the situation is different in subjects with hypothyroidism in whom certain components of tobacco such as thiocyanates seem to reduce the secretion of thyroid hormones and with the consequence of exacerbating the disorders of the disease. Smoking is classically associated with an enlargement of the thyroid gland. An increased risk of developing non-toxic multinodular goiter has been demonstrated in smokers, particularly in women. Proof of this is the reduction of the impact of smoking on thyroid volume by dietary iodine supplementation. In Graves’ autoimmune hyperthyroidism, the risk of developing an ocular pathology (orbitopathy) is aggravated in smokers. It can be a simple exophtalmia (bulging eyes) or more serious complications. The severity of orbitopathy has been shown to be related to the level of tobacco intoxication. There appears to be an inverse relationship between smoking and the risk of Hashimoto’s autoimmune hypothyroidism. The anti-inflammatory effect of nicotine on the immune system is a hypothesis that may explain this reduction in the risk of thyroid autoimmunity in connection with tobacco intoxication. It has also been shown that there is a reduced risk of thyroid cancer in patients with tobacco intoxication. This could be explained by the fact that the level of TSH is reduced in smokers and that it is known that the risk of developing a differentiated thyroid cancer is influenced by the level of TSH. During pregnancy, maternal smoking exposes to fetal thyroid abnormalities, both functional and morphological, which means that smoking cessation assistance must be offered to all women planning pregnancy.