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Smoking and Thyroid Disease

The habit can increase your risk of a thyroid issue – and make one worse

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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.

Thyroid Function

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

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.

Hashimoto’s Disease

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.  

Goiter

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.

Eye Problems

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

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.

Vaping

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.

Does Marijuana Adversely Impact the Endocrine System?

More than 22 million Americans use marijuana, both medicinally and recreationally, according to the National Institute of Drug Abuse, and that number can be expected to rise as more states make its use legal. Cannabis is known to improve pain tolerance 1 and can stimulate the appetite in patients whose illnesses and treatment regimens inhibit appetite.

Given the limited understanding of how marijuana affects the endocrine system, a group of researchers set out to discover whether marijuana has an effect on thyroid function and autoimmune conditions.

People who are obesity and/or have diabetes should not smoke marijuana given its role in activating endocannabinoid receptors, which may increase hunger and have an adverse effect on the metabolic system, including blood sugar and body weight.

The team from the Albert Einstein College of Medicine and Maimonides Medical Center, both in New York, examined data from the National Health and Nutrition Examination Survey (NHANES) of adults who had thyroid laboratory results and responses to a questionnaire about marijuana use for frequency. 2 Results were separated by those who had used it in the past (more than 30 days ago) or were current users (within the last 30 days).

“Our data analysis suggested that among recent marijuana users, the rate of TSH level within the normal range was significantly higher than the rate of TSH within the normal range of subjects who reported past use or never used marijuana,” study author, Roja Motaghedi, MD, told EndocrineWeb.

The researchers found that the most recent marijuana users were significantly less likely to exhibit elevated thyrotropin (TSH) and anti-thyroperoxidase antibody (TPOAb) levels than past users or non-users. 2 Once the data were controlled for confounding factors, recent marijuana use still correlated with a TSH level below 5.6 IU/mL, although not with a negative TPOAb level.

Fortunately, the most recent users tended to be younger males, 2 a group that does not typically suffer from diabetes or thyroid issues.

“However, data on amount and timing of marijuana use was collected from self-reported questionnaires and could be biased,” said Dr. Motaghedi, associate professor of clinical pediatrics at Albert Einstein College of Medicine, in New York. Some of the answers seemed to be exaggerated, and I would imagine some subjects did not report accurately due to privacy issues surrounding the topic.”

Dr. Motaghedi also noted that her team did not have information on which subjects might have active thyroid disease or what medications they might be taking, preventing them from going so far as to recommend marijuana as a thyroid or endocrine system treatment. The study also didn’t gather data on how frequently current cannabis smokers smoked, which potentially could have affected their bloodwork.

Marijuana’s Effect on the Endocrine System

At this point, it is reasonable to say that people who should not be smoking marijuana include those who are obese and/or have diabetes, said Elena Christofides, MD, an endocrinologist and editorial board member of EndocrineWeb.

“We know that activation of endocannabinoid receptors does increase hunger,” she said, adding that the effects go beyond appetite and include having an adverse impact on the metabolic system, including blood sugar and body weight.

Her assertion is bolstered by the National Institutes of Health’s the Coronary Artery Risk Development in Young Adults (CARDIA) study, 3 which looked at marijuana and blood-sugar levels in 3,034 participants 25 years after they were first assessed for cardiovascular risks in the 1980s. Participants who indicated that they were still using cannabis had a 65% higher risk of prediabetes than those who were not. And, adults who said that they had smoked at least 100 times in their life had a 49% higher risk of prediabetes. The risk of cannabis use did not appear to extend to the development of type 2 diabetes.

However, several other studies have had results that contradict the CARDIA study findings. A Harvard Medical School study found lower fasting insulin levels and less insulin resistance among marijuana users 4 and Michigan State University researchers analyzed eight different studies with findings that indicated a 30% reduction in diabetes risk among marijuana users. 5

Best Practice Tips When Advising About Marijuana Use

Dr. Christofides welcomes studies that focus on marijuana use, considering the drug’s popularity and increasing legal status.

“I’m glad to see that some of the prejudices about looking at marijuana use are going by the wayside,” she said. However, clinicians must be prepared to address the temptation for use as an educational opportunity.

She recommended that endocrinologists do the following:

  • Ask about marijuana use in all patients, particularly the ones with diabetes and/or who are obese. Dr. Christofides finds that these patients tend to be unaware of their particular risks.
  • Actively recommend against marijuana use if patients are diabetic and/or obese.
  • Be nonjudgmental. Recognize that the stigma of marijuana is receding and invite open discussion.
  • Let patients know that the medical community is still largely unaware of the impact of marijuana on the endocrine system.
  • If patients indicate that they may want to begin smoking marijuana (in permitted states), recommend regular blood work that can be used as a baseline for new symptoms or abnormal lab results down the road.

View Sources

1. Russo EB. Cannabinoids in the management of difficult to treat pain. Ther Clin Risk Manag. 2008;4(1):245–259.

2. Malhotra S, Heptulla RA, Homel P, Motaghedi R. Effect of Marijuana Use on Thyroid Function and Autoimmunity. Thyroid. 2016 Published online ahead of print. December 5, 2016.

3. Bancks MP, Pletcher MJ, Kertesz SG, Sidney S, Rana JS, Schreiner PJ. Marijuana Use and Risk of Prediabetes and Diabetes by Middle Adultood: the Coronary Artery Risk Development in Young Adults (CARDIA) Study. Diabetologia. 2015;58(12):2736-44.

4. Prenner EA, Buettner H, Mittleman MA. The Impact of Marijuana Use on Glucose, Insulin, and Insulin Resistance among US Adults. Am J Med. 2013;126(7):583-589.

5. Alshaarawy O, Anthony JC. Cannabis Smoking and Diabetes Mellitus: Results from Meta-analysis with Eight Independent Replication Samples. Epidemiology. 2015;26(4):597-600.

Cannabis is known to have a positive role in reducing pain but its effect on metabolism and the endocrine system appear less favorable. Researchers examined the use of cannabis in thyroid function, finding a significantly elevated TSH among current users who were typically young males whose risk of thyroid or diabetes is low.