Histamine and Hashimoto's

Histamine is an important immune system chemical that is released by cells during hypersensitivity or inflammatory responses. Simply put, when your body is exposed to an allergic compound, histamine spikes and activates inflammation to protect the body from that compound. 

Histamine causes smooth muscle to contract and blood vessels to dilate, allowing immune cells to migrate to the site of a perceived attack. In normal amounts in the body, histamine helps with circulation, alertness, and digestion, and is also considered a neurotransmitter.

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Your body's cells produce histamine, as do some bacteria and yeast in your digestive tract. Histamine is also present in certain foods.


Histamine is associated with allergic or sensitivity reactions. In the spring, when the pollen is out, many people experience watery eyes, runny noses, and itchy skin. This is a histamine reaction. You've probably heard of antihistamines or supplements designed to dampen these types of reactions.

How Does Histamine Relate to DAO?

DAO, or diamino oxidase, is an enzyme produced by healthy intestinal cells that break down histamine in the small intestine. HNMT (Histamine N-Methyltransferase) is the enzyme responsible for breaking down histamine in the body, but when it comes to histamine intolerance, I'm mainly referring to DAO and its role in the digestive system.

digestive system

The body's preferred state is having a good balance between histamine levels and DAO enzymes in the digestive tract.

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What is Histamine Intolerance?

Simply put, histamine intolerance occurs when there are not enough DAO enzymes to balance histamine levels in the digestive system.

Unlike a true allergy, histamine intolerance may not be an immediate reaction. Histamine levels build up over time because the body cannot keep up with DAO production or histamine levels are too high. 

As I mentioned earlier, the body produces histamine, but histamine also enters the body through food. Bacteria in food can produce and release histamine, and other foods can cause the body to release histamine.

Symptoms of Histamine Intolerance

Symptoms of histamine intolerance are widespread and can be nonspecific, making the diagnosis of histamine intolerance difficult. Histamine intolerance can often be confused with food allergy, food sensitivity, mast cell disorder, and other diagnoses.

food allergy

People with histamine intolerance may experience some of the symptoms listed below, but not others. Gas may be the most common symptom, along with bloating after a meal, diarrhea, abdominal pain, and constipation. These symptoms may resemble the symptoms of SIBO.

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Common Histamine Intolerance Symptoms

  • Stomach pain, cramping
  • Nausea, vomiting
  • Diarrhea, constipation
  • Headaches and migraines
  • Low blood pressure
  • Heart arrhythmia
  • Hives, itching, flushing
  • Runny nose
  • Swelling in the face, mouth, or throat
  • Asthma
  • Fatigue
  • Dysmenorrhea (menstrual cramping)

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The Histamine and Thyroid Connection

Those with thyroid imbalances, including Hashimoto's, may be more prone to histamine intolerance. This may be because histamine intolerance and Hashimoto's thyroiditis can share the same root causes, including:

  • Sensitivity to gluten
  • Leaking intestine
  • SIBO
  • Allergy to IgE

leaky gut

Additionally, in an attempt to cure the thyroid, some may inadvertently increase histamine-rich foods in their diets, find themselves deficient in the DAO enzyme, or unknowingly consume substances that block DAO. I will cover each of these topics below in the treatment section.

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Diagnosis and testing 

Tests and diagnoses for histamine intolerance are on the rise. Currently, many functional doctors and naturopaths test blood levels of DAO as an indicator of the body's ability to break down histamine. The urinary histamine test is also being developed and implemented as a new, and arguably much simpler, testing option. However, both tests may not be widely available yet.

Some may opt for a trial of a DAO supplement or histamine elimination diet to see if symptoms subside. These two options are described in more detail below.


Genetic testing can also be helpful. Finding SNPs (single nucleotide polymorphisms) in genes that code for DAO and HNMT enzymes can often provide a piece of the puzzle.

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Conventional treatments 

The traditional approach to treating histamine intolerance often involves medications such as antihistamines. If you suffer from seasonal allergies, you might already be tempted to turn to antihistamines, as the symptoms can be similar. The benefit of antihistamines could be temporary relief. However, they do not address the root cause and therefore are not the most effective solution.

Antihistamines can also decrease the production of DAO in the body.

High Histamine Foods to Avoid

These foods are either high in histamine themselves, or cause mast cells in the body to release more histamine:


  • Alcohol, including fermented alcohol (wine, beer)
  • Dried fruit
  • Chocolate
  • Bone broth (containing collagen)
  • Milk (dairy)
  • Wheat germ
  • Fermented foods (sauerkraut, kimchi, vinegar, kefir, yogurt, kombucha)
  • Pickled foods (olives, pickles)
  • Cured meats (lunch meats, hot dogs, bacon, pepperoni)
  • Soured foods (sour cream, buttermilk, sourdough)
  • Canned, smoked, and fried fish/seafood (shellfish, tuna, mackerel, anchovies, sardines, smoked herring)
  • Aged cheese
  • Goat cheese
  • Food dyes and artificial sweeteners
  • Fresh fruits (bananas, papayas, strawberries, avocados, pineapples, raspberries, apricots, kiwis, nectarines, peaches, citrus)
  • Fresh vegetables (tomatoes, spinach, nightshades, fava beans, mushrooms)
  • Honey
  • Leftovers (best to avoid altogether, but make sure cooked foods are cooled rapidly and put right into the refrigerator; never reheat more than once)
  • Nuts
  • Pork

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Low Histamine Foods to Eat Often

  • Beef, poultry, and fish/seafood (very fresh or frozen)
  • Gluten-free grains (quinoa, rice, etc.)
  • Eggs
  • Olive oil
  • Coconut oil
  • Leafy herbs
  • Herbal teas
  • Milk alternatives (coconut, hemp, almond)
  • Fresh vegetables (except those listed as AVOID)
  • Fresh fruits (apples, pears, cantaloupe, grapes, watermelon, mango)

gut health

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Steps to take 

  • Focus on your gut health. This is the very first place to start when it comes to histamine and your thyroid. Bacterial imbalances, leaky gut, SIBO, and infections all impair your ability to break down histamine.
  • Make sure you're getting all the essential nutrients to support optimal thyroid function. Keep in mind that lower thyroid function can raise your histamine levels.
  • Consider Factors That May Increase Your Histamine Load
    • Histamine-Rich Foods
    • Foods that block the DAO enzyme
    • Focus on Alcohol, as it can increase histamine levels.


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