Table 3.

Overview of human cigarette smoking and thyroid function studies.

Population	Smoking status	Main findings	Citation	Interpretation
Grave’s hyperthyroidism	Chronic smokers	47.9% of Grave’s disease	Bartalena et al. (1989)	Grave’s patients smoke at extremely high rates compared to the general population
Grave’s hyperthyroidism	Chronic smokers	64.2% of Grave’s opthalmopathy	Bartalena et al. (1989)
Grave’s hyperthyroidism	Chronic smokers	1.9× ↑ risk of Grave’s disease	Prummel and Wiersinga (1993)	Smoking increases the risk of developing Grave’s disease and Grave’s opthalmopathy
Grave’s hyperthyroidism	Chronic smokers	7.7× ↑ risk of Grave’s opthalmopathy	Prummel and Wiersinga (1993)
Euthyroid	Chronic smokers	↑T3, ↔T4, ↔TSH	Christensen et al. (1984)	Smoking increases one measure of thyroid function (T3)
Euthyroid	Former smokers	↔T3, ↔T4, ↔TSH	Christensen et al. (1984)	Smoking increases one measure of thyroid function (T3)
Euthyroid	Chronic smokers	↔T3, (n.d.)T4, ↓TSH	Ericsson and Lindgarde (1991)	Smoking increases thyroid function (only in indirect measurement)
Euthyroid	Former smokers	↔T3, (n.d.)T4, ↓TSH	Ericsson and Lindgarde (1991)
Euthyroid	Chronic smokers	(n.d.)T3, ↑T4, ↓TSH	Fisher et al. (1997)	Smoking increases thyroid secretion
Euthyroid	Chronic smokers	(n.d.)T3, (n.d.)T4, ↓TSH	Asvold et al. (2007)	Smoking increases thyroid function (only indirectly assessed)
Euthyroid	Former smokers	(n.d.)T3, (n.d.)T4, ↓TSH	Asvold et al. (2007)
Euthyroid	Chronic smokers	↑fT3, ↑fT4, ↓TSH	Vejbjerg et al. (2008)	Smoking increases thyroid hormone function
Euthyroid	Secondhand smoke	↑T3, ↑fT4, (n.d.)TSH	Metsios et al. (2007) and Flouris et al. (2008)	Smoking increases thyroid hormone function
Euthyroid	Chronic smokers	↓fT3, ↓fT4, ↑TSH	Soldin et al. (2009)	Smoking decreases thyroid hormone function
Euthyroid	Secondhand smoke	↓fT3, ↓fT4, ↑TSH	Soldin et al. (2009)	Smoking decreases thyroid hormone function
Euthyroid	Chronic smokers	↑fT3, ↑fT4, ↓TSH	Jorde and Sundsfjord (2006)	Smoking increases thyroid hormone function
Euthyroid	Filtered cigarette smokers	↔T3, ↓T4, ↑TSH	Banerjee and Muthu (1994)	Smoking reduces thyroid function
Euthyroid	Non-filtered cigarette smokers	↔T3, ↓T4, ↑SH	Banerjee and Muthu (1994)	Smoking reduces thyroid function
Euthyroid	Light and moderate smokers	↔T3, ↔T4, ↔TSH	Sepkovic et al. (1984)	Heavy smoking reduces thyroid function
Euthyroid	Heavy smokers	↓T3, ↓T4, ↔TSH	Sepkovic et al. (1984)	Heavy smoking reduces thyroid function
Hashimoto’s thyroiditis	Chronic smokers	76.4% hypothyroid	Fukata et al. (1996)	Smoking increases the rates of hypothyroidism in subjects with Hashimoto’s thyroiditis
Hashimoto’s thyroiditis	Former smokers	61.9% hypothyroid	Fukata et al. (1996)
Women 15–44 years old	Chronic smokers (≥31/day)	↑ rate of hypothyroxinemia normal rate of hypothyroxinemia	Vanderver et al. (2007)	Heavy smoking increases rate of severe low T4 syndrome
Women 15–44 years old	Chronic smokers (≤30/day)		Vanderver et al. (2007)	Heavy smoking increases rate of severe low T4 syndrome
Euthyroid	Chronic smokers	↔T3, ↔ T4, ↔TSH	Muller et al. (1995)	Smoking reduces thyroid function in subclinical hypothyroid subjects
Subclinical hypothyroid	Chronic smokers	↔T3, ↓T4, ↑TSH
Hypothyroid	Chronic smokers	↔T3, ↔T4, ↔TSH
Hypothyroid	Former smokers (<1 year)	7.36× ↑ risk of hypothyroidism	Carle et al. (2012)	Smoking cessation increases the risk of developing overt hypothyroidism
Hypothyroid	Former smokers (1–2 years)	6.34× ↑ risk of hypothyroidism	Carle et al. (2012)

↓ = decrease, ↑ = increase, ↔ = no change, (n.d.) = not determined, fT3 = free T3, and fT4 = free T4.