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Smoking and Thyroid Disease
Exploration of the Connections

by Mary Shomon

When it comes to cigarette smoking and thyroid disease, there are three major questions that many patients have:

  • What is the relationship between smoking and thyroid disease?
  • Is it worse to smoke if you have thyroid disease? and
  • Is it a coincidence that a diagnosis of hypothyroidism sometimes comes not long after quitting smoking?

Let's take a look at the answers.

Tobacco smoke contains substances that affect the function of the thyroid. One component of tobacco smoke is cyanide, which is converted to thiocyanate, which acts as an anti-thyroid agent, directly inhibiting iodide uptake and hormone synthesis. There are many other components of smoke that might have antithyroid action; decrease the binding of triiodothyronine to its receptors or its post-receptor actions in the liver, muscle, or other organs; or both.

Studies show 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.

A journal article "Cigarette Smoking and the Thyroid," featured in the October 12, 1995 issue of The New England Journal of Medicine says 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, smoking decreases both thyroid secretion and thyroid hormone action.

There are specific relationships between thyroid disease and smoking that are also important to recognize.

Note: If You Don't Have Thyroid Disease, But Are Planning to Quit Smoking:
First...good for you. If you want to stay on top of your health, get a baseline Thyroid Function Test (known as a TSH test) before you quit. Then, after quitting, if you find that you have more than the small weight gain associated with quitting smoking, or if the common symptoms of having quit continue longer than normal, visit your doctor for a followup TSH test to see if you have an underlying thyroid condition.

The Longer and More You've Smoked, The More Risk of Thyroid Disease You Face

A March 2000 study reported on in the Archives of Internal Medicine found that smoking is associated with an increased risk of developing clinically overt thyroid disease.Their data also suggested that cumulative cigarette consumption is a risk factor, most pronounced in autoimmune thyroid disease.

Smoking Increases the Risk of Graves' Disease

According to a Jan. 27, 1993 article in the Journal of the American Medical Association smokers are twice as likely as nonsmokers to develop Graves' disease. According to that research, smoking also apparently worsens eye problems in people with Graves' disease.

And the September 2000 issue of "Thyroid" reported on research suggesting that environmental factors such as smoking, rather than genetics, were likely to predispose certain individuals with autoimmune thyroid disease to severe Graves' disease.

Smoking Increases the Risk of Thyroid Eye Disease

The most dramatic effect of smoking on the thyroid is its association with Graves' hyperthyroidism, and especially with Graves' ophthalmopathy.

According to the Jan. 27, 1993 JAMA study, smoking also worsens eye problems in people with Graves' disease.

Researchers have also recently learned that smoking reduces the effectiveness of treatments for thyroid eye disease. The researchers reviewed the outcomes of 300 Graves' disease patients with mild eye symptoms treated with radioiodine alone or with steriods, and 150 with serious eye complications who received steroids and radiation therapy for their thyroid eye disease.

Among Graves' disease patients who had milder eye symptoms, smokers were more likely to progress to more serious thyroid eye disease than nonsmokers. Radioidone and steroid treatment for thyroid eye disease was also four times more effective in dealing with the eye symptoms for nonsmokers than smokers. This same relationship also applied to patients with more serious thyroid eye disease. ("Smoking affects Graves' disease treatment," Annals of Internal Medicine, 1998;129:632-635.)

Smoking Increases the Risk and Severity of Hashimoto's Disease

One study also suggests that that smoking may increase the risk of hypothyroidism in patients with Hashimoto's thyroiditis. .

The Relationship Between Quitting Smoking and Thyroid Disease Onset

Back in 1996, I posted a request the Usenet newsgroup for anecdotal information from other women who, like me, were diagnosed hypothyroid after stopping smoking. I stopped smoking in July of 1995, and it was not too long after that I was diagnosed as hypothyroid. So I began to wonder about the relationship between thyroid disease and smoking.

I received a large number of responses from women who said had the same experience -- diagnosed with hypothyroidism not long after stopping smoking.

While I don't have an answer as to whether or not stopping smoking somehow "triggers" or unmasks problems with the thyroid -- there anecdotally appears to be some connection.

In a poll I conducted with almost 1000 thyroid patients, 11 percent of the respondents were diagnosed with thyroid disease within 3 months of quitting smoking. And 18% were diagnosed within 6 months of quitting smoking.

My theory is that smoking/nicotine creates an artificially high metabolism that masks the fatigue/lethargy commonly seen in hypothyroidism. When the smoker quits, this masking is removed, and the full effects of hypothyroidism on the metabolism and thyroid are felt.

And, for smokers with undiagnosed thyroid dysfunction, without proper thyroid hormone treatment, stopping seems to be a metabolic/weight gain double whammy, as they lose the appetite suppressant, metabolism-upping effects of nicotine, and experience the full effects of the hypothyroidism.

Why You Should Quit?

If you have thyroid disease, you should quit smoking now!! Smoking can and often will worsen your existing thyroid problem, and if you have Graves' Disease or Thyroid Eye Disease, you absolutely must quit smoking to help prevent further progression of problems or worsening of your eye problems.

There are many effective ways to quit, and you can find out about them all at Christine Rowley's excellent Quit Smoking Website at

I've been there, too, so maybe I can help as well. Read the story of how I personally quit smoking in July of 1995, after smoking for 15 years.

Sticking Out Our Necks and this website are Copyright Mary Shomon, 1997-2003. All rights reserved. Mary Shomon, Editor/Webmaster
All information is intended for your general knowledge only and is not a substitute for medical advice or treatment for specific medical conditions. You should seek prompt medical care for any specific health issues and consult your physician or health practitioner before starting a new treatment program. Please see our full disclaimer.