Smoking and Thyroid Disease
The habit can increase your risk of a thyroid issue – and make one worse
Do-Eun Lee, MD, has been practicing medicine for more than 20 years, and specializes in diabetes, thyroid issues and general endocrinology. She currently has a private practice in Lafayette, CA.
There is no single organ system of the body in which cigarette smoking is anything less than harmful. While focus is often placed on the effects of smoking on the lungs, heart, and skin, the thyroid gland can be hurt just as much. On one hand, smoking can worsen symptoms related to hypothyroidism and Hashimoto’s disease. But it can also increase the risk of developing disorders like Grave’s disease in the first place.
As smoking habits continue to change in the United States, with the popularization of vaping and the legalization of marijuana in many states, an increased focus has been put on the impact of these activities, if any, on thyroid health as well.
Tobacco smoke contains substances that affect both the function of the thyroid gland and the thyroid gland itself. One of the components of tobacco is cyanide which, when smoked, is converted to the chemical thiocyanate. Thiocyanate is known to interfere with thyroid function in three key ways:
- It inhibits the uptake (absorption) of iodine into the thyroid gland, reducing the production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3).
- It directly inhibits hormone production by interfering with the synthesis process in the thyroid gland.
- It increases the excretion of iodine from the kidneys, increasing the risk of thyroid gland inflammation and such constitutional symptoms as fever, nausea, and stomach pain.
In people with hypothyroidism (low thyroid function), a drop in T3/T4 levels can complicate symptoms of fatigue, weight gain, and mood swings, and potentially take back many of the gains afforded by treatment.
With that being said, the impact of thiocyanate on the thyroid gland is mediated by nicotine in cigarettes. Nicotine actually has a converse effect on the thyroid gland, activating the function and undercutting some of the inhibitory effects of thiocyanate.
Concerns in Autoimmune Thyroid Disease
The persistent inflammation caused by cigarette smoking can also result in the enlargement of the gland itself, which is of particular concern to people living with Graves’ or Hashimoto’s disease.
Graves’ disease, a form of autoimmune hyperthyroidism characterized by thyroid enlargement (goiter), occurs twice as frequently in smokers as in non-smokers. Moreover, in persons living with the disease, smoking is associated with faster disease progression, the deterioration of symptoms, and a poorer response to thyroid treatment.
The association between smoking and Hashimoto’s disease, an autoimmune disorder linked to hypothyroidism, is not as clearly defined. What is known, however, is that smoking appears to further diminish thyroid function while spurring the development of goiters, particularly in iodine-deficient people.
In populations with high iodine intake, smoking increases the risk of Hashimoto’s hypothyroiditis, according to research from the University of Cincinnati. This includes the United States where the average daily intake is twice the recommended limit.
There is also evidence that smoking increases the risk of goiter irrespective of the number of cigarettes smoked. According to research published in Thyroid Research and Practice, the association was mostly seen in younger women and elderly people. Younger women tended to have diffuse thyroid enlargement, while older people typically had multinodular goiters. For unknown reasons, smoking doesn’t appear to be associated with a solitary thyroid nodule.
The risk of smoking-induced goiter is believed to be highest in populations with an iodine deficiency. This is seen in countries like the Philippines where goiter is prevalent, mild iodine deficiency is endemic, and 28% of the population smokes.
One of the more profound effects of smoking is its impact on vision, most predominantly in people with Graves’ ophthalmopathy (a condition characterized by swollen, bulging eyes).
A study conducted in 2014 concluded that smokers with Graves’ disease were more likely to experience rapid eye deterioration, including the development of double vision, the constriction of eye movement, and irreversible optic nerve damage.
More concerning yet is the fact that treatment of Graves’ ophthalmopathy (traditionally with steroids and radioiodine) is seen to be four times less effective in smokers than in non-smokers.
Thyroid cancer is today the eighth most common cancer in women. While it may seem logical to assume that smoking is a risk factor, as it is with lung and throat cancer, studies thus far have been largely contradictory.
A study released in 2012 reported that among 331 women with thyroid cancer, there was no difference in the incidence of disease between women who smoked and those who didn’t. In fact, the study suggested that smokers had a modest reduction in thyroid cancer risk, a result the investigators found “disquieting.”
Other studies have since mirrored the results, albeit more in differentiated (mature) cancers than undifferentiated (immature) cancer.
It is possible that smoking may have a greater impact on a developing thyroid tumor than an existing one.
As more people turn to cigarette alternatives, interest in the health effects of practices like vaping (smoking e-cigarettes) is sure to grow. Unfortunately, little is known about the impact of these options on the thyroid.
Compared to tobacco and even cannabis, scientists know far less about the effects of vaping on thyroid function.
What has come to light in recent years is that nicotine withdrawal is associated with a drop in T3/T4 levels, according to research from Temple University in Philadelphia. What this suggests is that nicotine replacement via vaping or other means may help maintain hormonal output in people with thyroid problems who are trying to quit. With that being said, vaping is increasingly being linked to lung illnesses. This has prompted the Centers for Disease Control and Prevention (CDC) to recommend refraining from all vaping products.
Thyroid hormone replacement therapy, using the drug levothyroxine, also appears to minimize symptoms of nicotine withdrawal. This means that people on levothyroxine who are planning to quit may benefit from frequent blood monitoring and an increase in their levothyroxine dose as needed.
A Word From Verywell
Whatever perceived benefits cigarettes offer pales in comparison to the benefits of stopping. In the end, there is no overlooking the fact that smoking will only worsen thyroid symptoms, speed the progression of the disease, and make thyroid treatment less effective. This goes for all forms of thyroid disease, including thyroid cancer; smoking can increase the risk of metastasis, spreading cancer beyond the site of the tumor to other parts of the body.
Most insurance plans today offer free smoking cessation treatment as part of their annual benefits. If you have trouble kicking the habit, speak with your doctor about pharmaceutical options that may help.
Smoking and thyroid disease have a cause-and-effect relationship, increasing risk of Graves' disease while worsening symptoms of hypothyroidism.