Early in my health journey I noticed that I was becoming more intolerant to my environment. I reacted to foods, cosmetics, paint and noticed that I would get raging migraines, skin breakouts and server itching. This significantly worsened during my years of battling with SIBO. It literally felt that my list of tolerant foods and ‘items’ in the world around me were shrinking. It wasn’t until I started to address histamine, that I witnessed the close relationship between histamine, my thyroid and overall wellbeing.

Histamine and thyroid

What is histamine?

Histamine is a chemical that plays an important role in many processes in the body such as inflammation, immunity, neurotransmitter modulation and stomach acid secretion. Its primary role is to protect the body from allergic compounds. When your body is exposed to a compound like pollen for example, your immune system, in particular your mast cells, will fire off histamine and thus set off the alarm for your immune system to target the potentially dangerous compound. This can leave you with symptoms such as sneezing, coughing, runny nose, headaches, itching and in some extreme cases can be life-threatening.

The example of pollen is what we call ‘classic’ histamine release (immunological). This is a process where the antigen (pollen) induces IgE antibodies that prompts both mast and basophil cells (immune cells) to degranulate stored histamine after binding to membrane receptors. There are four different histamine receptors that have different physiological locations and actions in the body.

The second type of histamine release, known as non-immunological also involves the degranulation of stored histamine from mast and basophil cells. This type can be induced by alcohol, food and medication and is typically what I see most in the clients that I work with.

Histamine is not just produced by your immune cells, but also certain bacteria in your gut.

Histamine Thyroid Connection

Location of histamine receptors

As mentioned above, histamine is secreted by mast cells and basophils (types of immune cells) which are found in connective tissue. The highest concentration of mast cells is found in the respiratory tract, conjunctiva, gastrointestinal tract, and skin. As mentioned earlier, there are four different histamine receptors. H1-receptors help to dilate blood vessels. H2-receptors, control the production of hydrochloric acid in the stomach. H3-receptors are involved with the histamine that act as a neurotransmitter, sending signals between your brain and body to support sleep, behaviour, mood, appetite. You can also find histamine receptors in the lungs, thymus, spleen, tonsils, trachea, liver, small intestine, and colon (via H4-receptors).


Key functions of histamine

  • Protection against invaders/infection
  • Regulate hormones
  • Supports healthy digestion
  • Acts as a neurotransmitter, therefore, impacts mood
  • Controls the production of stomach acid
  • Help regulate immune function.

Histamine Intolerance

Histamine intolerance is a lot more common than I realised when I first embarked on my journey. It is the consequence of too much histamine in the body and the inability to break it down effectively. There are many factors that can contribute to dealing with high levels of histamine.

Some individuals have unstable mast cells that release too much histamine. Other individuals may have too many mast cells and thus too much histamine. In other instances the presentation of allergies results in higher levels of histamine being produced at times. Food, medication, and stress can all play a role in histamine intolerance.

As can your genetics. There are four genetic pathways that play a key role in histamine metabolism, and they are DAO, HNMT, NAT2 and CBS.

Histamine Thyroid Connection

Your Genes

The enzyme diamine oxidase (DAO) is the most well-known enzyme involved in the breakdown of histamine. Lower levels of DAO can impact how efficiently you metabolise histamine. I am one of these individuals. It is important to note that DAO is not found in the central nervous system. Instead, this is where HNMT will control histamine.

Histamine N-Methyltransferase (HNMT) is a protein coding gene found in the central nervous system. Its key function is to transfer a methyl group from S-adenosyl-l-methionine (SAM) to histamine.

NAT2 is an alternative pathway that convert histamine into acetyl histamine, which is then excreted in urine. If you have a genetic mutation on this gene, then it can ultimately lead to slower histamine breakdown.

It is also worth mentioning that any mutations on Cystathionine Beta Synthase (CBS) can lead to a depletion in SAMe (S-adenosyl-methionine), one of your major methyl donors, which can ultimately lead to an increase in histamine in the body.

My personal struggle with histamine is connected to a homozygous CBS (which basically means that I produce more sulphur, which can result in lower SAMe and thus higher histamine) coupled with a homozygous DAO (significantly reduction in the ability to break down histamine) and a heterozygous HNMT (reduced activity to break down histamine).

Understanding your genetics can help!

The way in which histamine intolerance expresses itself, varies from person to person.

Histamine Thyroid Connection

Symptoms of histamine intolerance



  • Runny nose
  • Sneezing
  • Coughing
  • Swelling in throat
  • Congestion
  • Phlegm
  • Asthma

Central Nervous System

  • Headache
  • Dizziness
  • Anxiety
  • Brain-fog
  • Pressure in head
  • Difficulty sleeping
  • Fatigue
  • Pain


  • Palpitation
  • Tachycardia
  • Arrhythmias


  • Diarrhoea
  • Abdominal pain
  • Cramping
  • Bloating
  • Reflux
  • Nausea


  • Menstrual Irregularities
  • Heavy bleeding
  • Painful cramping
  • Menstrual headaches


  • Skin rashes
  • Spots
  • Redness
  • Hives
  • Itching
  • Flushing
  • Severe sweating

Histamine and your thyroid

There is a close interplay between histamine and your hormones and especially your thyroid. There is evidence to suggest that lower thyroid function can upregulate mast cells, which in turn can increase histamine production. In the same breath sluggish thyroid function can result in lower levels of the DAO enzyme being produced. Add some fermented food, a leaky gut and small intestinal bacterial overgrowth (SIBO) and you have the potential to end with a bad case of histamine intolerance.

There is no doubt that excess histamine can lead to the development of SIBO. This in turn can reduce the DAO enzyme needed to break down histamine. Furthermore, SIBO also produce histamine, which then adds further fuel to the fire.

Various studies have identified the connection between SIBO and Hypothyroidism and it is therefore important to consider the role that histamine may be playing in your overall health.

Ultimately thyroid issues can lead to histamine intolerance, and it may be helpful to understand just how you can support yourself to lower your histamine load.

Steps to take

  1. Focus on your gut health. This is the very first place to start when it comes to histamine and your thyroid. Imbalance in bacteria, leaky gut, SIBO, infections will all be compromising your ability to break down histamine.
  2. Ensure that you are getting all the key nutrients to support optimal thyroid function, remember lower thyroid function, can increase your histamine load.
  3. Consider the factors that can be increasing your histamine load
    • Histamine-rich food
    • Food that blocks the DAO enzyme
    • Stress
    • Alcohol since it can increase histamine levels.

In my group programme we look at the different types of food that can impact thyroid function, with histamine being one of them. It can sometimes be difficult to navigate the low histamine diet and people often find that specific support can be incredibly helpful.

If you want to understand more about which food to avoid, then you can download my high histamine food list.

If you are tired of trying to navigate your own health and not getting the results you are looking for, then book in for a free breakthrough call where we can discuss your health in more detail and look at the best possible options for you to get back to feeling your best.

Nutritional Therapist Cheshire, Health, Nutritionist Cheshire, Functional Medicine Cheshire, Rootcause Solution