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Smoking stimulates thyroid-gland secretion
The background of the study. Smoking may stimulate thyroid hormone secretion, in addition to being a risk factor for hyperthyroidism and eye disease caused by Graves’ disease. In this study, the relationships between smoking and pituitary–thyroid function were studied in a large number of subjects.
How the study was done. The study group consisted of 30,834 adults living in one county in Norway. None had a history of thyroid disease, and all provided information about smoking, including the age at which they had started smoking, the number of years they had smoked, the number of cigarettes smoked daily, and if and when they had stopped smoking. Serum thyrotropin (TSH) was measured in all the subjects and free thyroxine [T4] was measured in those with abnormal serum TSH concentrations.
The results of the study. The average serum TSH concentrations in both women and men were highest in the never smokers and lowest in the current smokers (Table).
| Table. Geometric Mean Serum TSH Concentrations in 30,834 Never Smokers, Former Smokers, and Current Smokers. | ||
| Women | No. | Serum TSH (mU/L) |
| Never smokers | 10,622 | 1.66 |
| Former smokers | 4,240 | 1.61 |
| Current smokers | 5,577 | 1.33 |
| Men | ||
| Never smokers | 3,295 | 1.70 |
| Former smokers | 4,037 | 1.61 |
| Current smokers | 3,023 | 1.40 |
Among the patients who had stopped smoking, the average serum TSH concentrations increased gradually with time after cessation of smoking, especially in women. Among current smokers, serum TSH concentrations were lower in those who smoked more often. For example, among the women, the mean serum TSH concentrations were 1.61 mU/L in the never smokers and 1.30 mU/L in those who smoked >13 cigarettes daily. The results were similar among the men.
Among the women, the frequency of high serum TSH concentrations was higher in the never smokers than in the current smokers. The results in the men were similar, although fewer men had high serum TSH concentrations. Conversely, low serum TSH concentrations were more frequent in women who were current smokers than in those who had never smoked (few men had low serum TSH concentrations).
The conclusions of the study. Smokers have lower serum TSH concentrations and a lower prevalence of hypothyroidism as compared with nonsmokers, and among women a higher prevalence of hyperthyroidism.
The original article. Asvold BO, Bjøro T, Nilsen TI, Vatten LJ. Tobacco smoking and thyroid function: a population-based study. Arch Intern Med 2007;167:1428-32.
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| Thyroid Digest Index | | | November 2007 Thyroid Digest |
