Does Smoking Cessation Cause Hypothyroidism?

A Closer Look at Smoking Cessation, Weight Gain and Hypothyroidism

Woman applying a nicotine patch
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Many people first notice that they have thyroid disease after they quit smoking. This phenomenon makes people think that smoking cessation leads to thyroid disease.

Tobacco and the Thyroid

Tobacco smoke contains substances that affect the function of the thyroid. Studies have shown that smokers are more likely to have thyroid enlargement, and it is possible that mild thyroid enlargement in smokers could be a sign of subtle thyroid disturbance.

Research Connecting Smoking and Thyroid Disease

Some research suggests that smokers are twice as likely as nonsmokers to develop Graves' disease and smoking worsens eye problems in people with Graves' disease.

One study suggests that that smoking may increase the risk of hypothyroidism in patients with Hashimoto's thyroiditis. Results from another study suggest that smoking is associated with so many abnormalities of thyroid function that it is unlikely it has just one single effect on the thyroid gland.

In women with hypothyroidism, one study suggests that smoking decreases both thyroid secretion and thyroid hormone action. However, the study results do not indicate that smoking causes hypothyroidism, only that it increases the severity and effects of hypothyroidism.

How Does Smoking Affect Thyroid Secretion or Action?

One component of tobacco smoke is cyanide, which is converted to thiocyanate, which inhibits iodide uptake and hormone synthesis.

There are many other components of smoke that might have antithyroid action, too.

The most dramatic effect of smoking on the thyroid is its association with Graves; hyperthyroidism, and especially with Graves ophthalmopathy. Whether smoking predisposes a person to Graves; hyperthyroidism is unclear.

Finally, smoking is also linked to the development of autoimmune thyroiditis.

Smoking Cessation, Weight Gain and Hypothyroidism

Researchers have yet to elucidate a clear causal relationship between smoking cessation and hypothyroidism. However, although there are conflicting findings on the subject, there is some association between these two factors.

Please consider the following two points:

  • The risk of developing hypothyroidism increases six-fold within 2 years of smoking cessation.
  • Certain studies have shown that levels of thyroid antibodies increase after smoking cessation.

One interesting hypothesis links smoking cessation to hypothyroidism and weight gain. Specifically, when a person quits smoking, the weight gain that often accompanies smoking cessation is attributable to hypothyroidism.

So What Does All This Mean?

Please don't interpret an association between smoking cessation and hypothyroidism as an excuse to continue smoking to somehow prevent hypothyroidism. If you smoke you must stop no matter what.

Smoking is not only bad for your thyroid but your lungs, heart and entire body.

Instead, the association between smoking cessation and hypothyroidism should increase your awareness of possible hypothyroid symptoms (think cold intolerance, fatigue, dry skin, weight gain and depression) and raise your awareness that you may be at increased risk for hypothyroid disease. It may be a good idea to have your physician regularly check your thyroid after you quit smoking especially if you have a family history of thyroid disease.

Selected Sources

Abstract titled "Weight Gained after Cessation of Smoking May Be Caused by Onset of Hypothyroidism" by JH Mestman published in Clinical Thyroidology in 2012. Accessed on 1/27/2016.

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