FREE Histamine Guide

The Thyroid-Histamine Connection

The Thyroid-Histamine Connection

They always say, “big things come in small packages.”  Related to the human endocrine system, this is especially true.  Just to put it in perspective, there are seven glands in each of us that regulate our human growth, development, metabolism, tissue and sexual function, reproduction, and mood.  So basically everything we do. So now try to picture when something in that enormous communication network is malfunctioning. Trying to figure out what the problem is when one system coordinates so many of our involuntary bodily functions is somewhat overwhelming, right?! Don’t worry, that’s what I’m here for!

Autoimmune thyroiditis, Hashimoto’s disease. 3D illustration showing antibodies attacking thyroid gland

The Thyroid Gland

Lucky for us, there are mountains of research on the thyroid gland, one of the seven glands in the endocrine system, and we continue to make leaps and bounds in our knowledge of this gland and what may be throwing off our groove.  If you’ve been reading my recent blog posts, I’m sure you’re well versed on the basic ins and outs of the thyroid. However, I do want to review a few topics that will be important in our later discussion of histamine.

Thyroid Disease

Not lucky for us, there are over 20 million people who have some form of thyroid abnormality.  It affects people of all ages and all races, but does tend to affect women 5-8 times more than men.  The 2 most common diseases are hyperthyroidism and hypothyroidism(1).


Hyperthyroidism occurs when the body creates too much of a thyroid hormone, resulting in all the cells in the body that respond to these hormones to “speed up.” Symptoms of hyperthyroidism include: increased irritability, muscle weakness, tremors, increased sweating, heart palpitations, weight loss, sleep disturbances, and heat sensitivity.  The most common form of hyperthyroidism is called Graves’ disease, which is an autoimmune condition that causes hyperactivity of the thyroid gland. These patients will occasionally experience vision changes or eye irritation due to inflammation of the tissue around the eyes(1).


Hypothyroidism is a gross under activation of the thyroid gland, which causes a decrease in overall metabolism and leads to chronic fatigue, weight gain, constipation, cold sensitivity, depression, reduced exercise tolerance, and irregular or heavy menses.  Hashimoto’s thyroiditis is the most common cause of hypothyroidism in the United States. It is an autoimmune condition in which antibodies attack the thyroid gland, leading to decreased thyroid hormone production and gradual decreased thyroid function until hypothyroidism is the result(1).

It is especially hard to diagnose because there are no characteristic features of Hashimoto’s that make it discernible from hypothyroidism.  This is what I was finally diagnosed with after years and years of tests with no answers. If this sounds like you, please know you are not alone, and I hope I just saved you some time and trouble!

Histamine Receptors


Sometimes, diagnosing a thyroid condition isn’t as simple as it sounds, which is why we need to change gears and add another player onto the field.  Histamine is a chemical involved in the inflammatory process and produced by mast cells all over the body. Normally when you think of histamine, you think of allergies, and you would be correct; however, similar to the endocrine system, they seem to have their business in many different things. For example, in the stomach, histamine controls the production of hydrochloric acid (H2 receptors).  In the brain and spinal cord (so the nervous system you don’t have any voluntary control over), histamine acts as a neurotransmitter, moving messages about sleep, appetite, and behavior all over the brain (H3 receptors). In the immune system, histamine functions as a vasodilator (H1 receptors). Histamine receptors are also found in the colon, liver, lung, small intestine, thymus, spleen, testes, tonsils and trachea (H4 receptors).  In a normal immune response, when the body senses a threat, histamine receptors will secrete an increased amount of histamine. The release of histamine will cause vasodilation of the blood vessels, allowing white blood cells to travel faster to the area of the threat and address it (2,3).


Histamine Intolerance

Histamine isn’t necessarily a problem until we don’t have the means to break it down. Histamine intolerance is an imbalance between the amount of histamine released and the ability of the body to break down the accumulating histamine.  DAO is the enzyme that is primarily responsible for breaking down histamines in the digestive tract of the body. Decreased DAO activity in addition to increased histamines may result in symptoms that are similar to one having an “allergic reaction” to something. Certain histamine-rich foods (See graphic below), as well as medications that cause excess histamine to be released and/or DAO enzymes to be blocked, can cause symptoms such as diarrhea, headaches, congestion, runny nose, breathing difficulties, low blood pressure, heart abnormalities, hives, asthma attacks, and skin issues like eczema or psoriasis, crawling sensations on the skin/scalp and more in people with a histamine intolerance. Because many of the symptoms of HIT mimic other conditions, it is likely that the presence of HIT in the general population is largely underestimated.  As many as 20% of HIT symptoms occur when histamine-rich foods are used in combination with DAO inhibitors, like alcohol and other common medications, like anti-histamines, antidepressants or histamine blockers.3 In my book, The 30-Day Thyroid Reset Plan, I talk about potential triggers that could be affecting the thyroid. These triggers happen to be the mostly the same for histamine intolerance, so please feel free to check that out for more information about HIT.

The simplest thing to try if you think you have HIT is to eat fermented and other high histamine foods to see if your symptoms increase.  If you consequently remove these foods for a week and see a difference in your symptoms, then it is likely you have a histamine intolerance. With thyroid issues alone, fermented foods are excellent choices but when someone is also dealing with histamine intolerance, we have to support the gut in a different way.  Fermented foods obviously involve more bacteria, which can actually increased the histamine content of the foods you eat that may not actually be considered histamine-rich.4

You would also assume antihistamine drugs would be helpful, but because they reduce the amount of DAO you produce, they would be counterproductive in someone with HIT.  Instead I recommend products with quercetin. Quercetin is a compound found in many fruits and vegetables that have natural anti-carcinogenic, anti-inflammatory, antiviral, antioxidant, and psychostimulant properties. Similarly, it also controls mast cell activity and has protective effects on the GI tract.5

A natural option I recommend to patients is a supplement called histo-relief, which include quercetin as one of its primary ingredients. This supplement supports immune function, as well as the body’s response to food and environmental factors. Using this can significantly reduce the symptoms of histamine intolerance and help you to tolerate more foods that can be contributing to your symptoms.

Why Are Some People More Susceptible to Histamine Intolerance?

There are several reasons someone may have decreased DAO activity. In my newest book, The 4-Phase Histamine Reset Plan, I go into all underlying causes and give you a detailed plan on how to stop histamine intolerance in it’s tracks. For this article, I will go into the mot common reasons for the development of HIT. First, there may be a genetic abnormality in the DAO gene, which limits its production, and decreases the amount of DAO you can produce, causing an issue breaking down histamine. These genes won’t be fully expressed until adulthood, which explains why 80% of individuals with HIT are middle-aged women over 40.3,4 However, the primary explanation for HIT is poor gut health. Small intestinal bacterial overgrowth (SIBO) & leaky gut specifically. In SIBO, there is an overabundance of bacteria, which results in histamine production from the proteins of undigested food. Common symptoms include bloating, diarrhea, abdominal pain, and weight loss. Just to clarify, some bacteria in the small intestine is normal; however, the type of organism in addition to the amount is important here.6 Usually organisms in the small intestine are gram-positive, but with SIBO, it’s common to find more gram-negative bacteria, like E. Coli and Klebsiella pneumoniae.7 While most are familiar with the type of havoc E.Coli can cause, Klebsiella can cause mucosal damage to the intestinal walls and lead to nutrient absorption issues, causing more serious problems like malnutrition, osteoporosis, etc.8 With leaky gut, intestinal permeability causes inflammatory stress in the body which leads to decrease in the DAO enzyme production.

Histamine Intolerance & The Thyroid

So I know I have given you quite a large number of letters that stand for something else to remember, so let me recap thus far. Low thyroid levels (hypothyroidism) typically cause an increase in the number of mast cells, which are the cells responsible for the production of histamine. Low DAO production will decrease the amount of histamine you can break down.  High histamine levels combined with low DAO, histamine-rich or fermented foods, may lead to small intestinal bacteria growth and potentially a histamine intolerance. Got it? Good. Let’s keep going.

In my experience, issues with the gut are the main cause for HIT because things like SIBO & leaky gut that can break down DAO. This effect is, of course, increased by any genetic abnormalities in the DAO gene, how much high histamine food you eat, as well as any thyroid issues that may also be present. The gut also plays a huge role in autoimmune disease and since a large majority of people with hypothyroidism have Hashimoto’s, issues with gut health are extremely important in both conditions and could be what primarily causes both issues.

One study looking at the relationship between SIBO and hypothyroidism reported that SIBO may be present in more than half of patients with hypothyroidism.9

Lauritano et al studied 90 subjects (hypothyroidism [n = 50] and control [n = 40]) and found that significantly higher numbers of patients (54%) with hypothyroidism have SIBO compared with the control group.  While larger studies obviously need to be done on these correlations, patients with persistent GI issues and a diagnosis of hypothyroidism may require additional testing to check for SIBO.10

With leaky gut, food particles, bacteria, and environmental toxins seep into the bloodstream and cause problems in the body.  This influx of foreign material into the blood causes the immune system to go haywire. The resulting tirade causes large amounts of inflammation that not only affects the particles the immune system is aiming for but also healthy issues, like the thyroid, brain, skin, and gut lining.  This can result in chronic disease and autoimmune-type symptoms. There also seems to be a relationship between leaky gut and autoimmunity, which means that having SIBO might cause a leaky gut, which in turn may lead to Graves’ disease or Hashimoto’s thyroiditis.6  

Final Thoughts

To sum it all up, thyroid issues can lead to histamine intolerance and high histamine levels can play a role the development of autoimmune thyroid disorders.  I spent years and years wondering what could possibly be wrong with me, and as I discovered, it certainly wasn’t just a thyroid problem, which is why medication addressing just the hormonal imbalance did not fully fix my symptoms.  I am hoping my experience with Hashimoto’s and HIT will help yours be shorter and easier and because of that, I always thoroughly check the gut and other things that can be an underlying trigger in all patients, whether they come to me with a thyroid issue, histamine intolerance or both. If you have been shuffled through the modern medical system, I would love to help you get a grip on your symptoms and take your life back.  Please stay tuned for my new book coming out about histamine intolerance and in the meantime, feel free to schedule a consultation with me so we can get to the root of your issues!

To help your health journey with thyroid issues, histamine intolerance, and other chronic symptoms and health issues, I have written two books and dedicated my work to help people like you in my functional medicine practice.

If you have thyroid imbalances or thyroid disease, I recommend reading and following the recommendations in my book, The 30-Day Thyroid Reset Plan: Disarming the 7 Hidden Triggers That are Keeping You Sick. You will learn everything you need to know about thyroid disease. I offer a 30-day plan to improve your health and my favorite thyroid-friendly recipes to nourish your body with delicious meals.

If you have symptoms of histamine intolerance and want to understand each step of this simple yet refined histamine intolerance recovery system, I recommend that you read my book, The 4-Phase Histamine Reset Plan: Getting to the Root of Migraines, Eczema, Vertigo, Allergies and More where I explain everything about histamine intolerance and each phase of the plan in detail. You will also find my favorite low-histamine recipes to nourish your body. 

If you are dealing with symptoms of thyroid issues or histamine intolerance, or are experiencing other chronic unexplained symptoms, I invite you to schedule a consultation with me. I can help to identify the root cause of your condition and recommend a personalized treatment plan to repair your body and regain your health and well-being. Schedule your consultation here.


  1. American Thyroid Association. Accessed 1/22/2019.
  2. Maintz, L. and Novak, N. Histamine and histamine intolerance.  The American Journal of Clinical Nutrition. Vol 85, Issue 5, 1 May 2007, pgs 1185-1196.
  3. Dr. David Jockers. Are You Suffering From Histamine Intolerance? Assessed 1/26/19.
  4. Natural Endocrine Solutions. Histamine and Thyroid Health. Accessed 1/29/19.
  5. Li, Y., Yao, J., Han, C., Yang, J., Chaundhry, M.T., Wang, S., Liu, H., Yin, Y. Quercetin, Inflammation and Immunity. Nutrients. 2016 Mar;8(3):167. doi: 10.3390/nu8030167.
  6. Natural Endocrine Solutions. SIBO and Thyroid Health. Accessed 1/26/19.
  7. Pyleris, E., Giamarellos-Bourboulis, E.J., Tzivras, D., Koussoulas, V., Barbatzas, C., Pimental, M. The prevalence of overgrowth by aerobic bacteria in the small intestine by small bowel culture: relationship with irritable bowel syndrome. Dig Dis Sci. 2012 May;57(5):1321-9. doi: 10.1007/s10620-012-2033-7.
  8. Dukowicz, A.C, Lacy, B.E, Levine, G.M. Small Intestinal Bacterial Overgrowth: A Comprehensive Review. Gastroenterol Hepatol (NY). 2007 Feb; 3(2): 112–122.
  9. Almandoz, J.P., Gharib, H. Hypothyroidism: Etiology, diagnosis, and management. Med Clin North Am. 2012;96:203–21.
  10. Lauritano, E.C., Bilotta, A.L., Gabrielli, M., Scarpellini, E., Lupascu, A., Laginestra, A., et al. Association between hypothyroidism and small intestinal bacterial overgrowth. J Clin Endocrinol Metab. 2007;92:4180–4.
  11. Schneider E1, Leite-de-moraes M, Dy-M. Histamine, immune cells and autoimmunity. Adv Exp Med Biol. 2010;709:81-94.



Hi, I am Dr. Becky Campbell. I work with men and women who’ve had a health set back and are willing to do whatever it takes to reach optimal health so they can perform their best in their careers and be fully present with their family again.