Histamine Intolerance: What to know about high histamine

Histamine is a natural substance the immune system produces in response to pathogens, allergens, and dietary histamine from foods. The production and release of histamine is normal — even crucial to our health — as histamine plays a role in regulating everything from our allergic response and sleep-wake cycle to our emotions, digestion, and cognition. 

However, issues can arise if the immune system produces too much histamine in response to stimuli — or we accumulate more histamine than the body can effectively eliminate. Either scenario can create an imbalance between the intake, release, and breakdown of histamine, leading to increased histamine levels in the body and a condition known as histamine intolerance. 

Histamine intolerance: what is it? 

Otherwise known as histamine sensitivity or histamine overload, histamine intolerance is both a metabolic disorder and a food intolerance. The condition affects the body’s ability to degrade and eliminate histamine, leading to increased levels of histamine in the body (histamine overload) and an intolerance to various histamine sources (histamine sensitivity). 

Common symptoms of histamine intolerance include:

• Rhinitis.
• Facial flushing.
• Itchy and irritated skin.
• Hot flashes and night sweats.
• Nausea and vomiting.
• Headaches.
• Heart palpitations.
• Concentration issues.
• Slowed cognition.
• Digestive issues.
• Alcohol intolerance. 

Most symptoms of histamine intolerance are nonspecific and inconsistent, often resembling allergies, other food intolerances, and associated conditions like mast cell activation syndrome (MCAS) and mold toxicity. Some individuals with histamine intolerance may also have MCAS, but this isn’t always the case. 

The main difference between MCAS and histamine intolerance is that MCAS involves the release of multiple chemical mediators — not just histamine. Chronic mast cell activation can trigger histamine intolerance, however. 

What causes histamine intolerance or histamine overload? 

Normally, the histamine we produce is quickly broken down and eliminated from the body by the enzymes diamine oxidase (DAO) and histamine N-methyltransferase (HNMT). These enzymes help degrade and eliminate histamine, preventing it from building up in the body and creating problems. 

If the activity of one or both of these enzymes is impaired, however, the body cannot effectively break down or eliminate the histamine it accumulates. This increases the risk of histamine overload, leading to symptoms of histamine intolerance. 

Several factors that reduce the function of the DAO and HNMT enzymes include:

• Genetic mutations in the DAO enzyme (DAO deficiency)
• Genetic mutations in the HNMT enzyme (HNMT deficiency).
• Enzyme-blocking substances in foods, beverages, medications, and supplements.
• Damages to the intestinal mucosa. 

Some research even suggests that intestinal dysbiosis and leaky gut may reduce DAO activity and increase histamine levels in the body, leading to histamine overload and symptoms of histamine intolerance. The risk may be even greater in the case of bacterial overgrowth (e.g. SIBO), as several types of bacteria can increase histamine production in the gut and cause intestinal inflammation. Examples of histamine-producing bacteria include Morganella spp., Klebsiella, and Escherichia spp. 

Dietary histamine & histamine intolerance

Along with impairments in breaking down and eliminating histamine, other potential causes of histamine intolerance include increased dietary histamine from foods, medications, and supplements. Several sources of dietary histamine include:

• High-histamine foods. These foods include canned meat; fermented foods; shellfish; matured cheese; and select fruits, vegetables, and legumes. 
• Leftover foods from previous meals. Leftovers contain enzymes and bacteria that produce high levels of histamine as time goes on, even when foods are properly sealed and refrigerated. 
• Histamine liberators. Histamine liberators are foods or medications that contain substances that cause the mast cells to release histamine into the body. Even when the foods themselves are low in histamine, histamine liberators can be problematic for those with histamine intolerance. 

To diagnose histamine intolerance and decrease histamine levels in the body, a histamine elimination diet is typically recommended as a starting point. This means gradually eliminating high-histamine foods and other dietary sources of histamine for about two to four weeks, including histamine liberators and foods or medications that block the activity of DAO and HNMT enzymes. The Swiss Interest Group Histamine Intolerance (SIGHI) lists several known histamine-liberating foods and medications on its website. 

Low-histamine foods to enjoy

When following a histamine-elimination diet, it’s best to focus on eating freshly prepared, low-histamine foods like eggs, fresh or frozen meat, coconut, potatoes, rice, corn, and a variety of low-histamine fruits and vegetables. Examples of plant foods that are low in histamine include:

• Apples
• Blueberries
• Peaches
• Cherries
• Sweet potatoes
• Asparagus
• Broccoli
• Cucumbers
• Onions

Some individuals may notice improvements in their histamine intolerance symptoms after two weeks of following a histamine elimination diet, while others may require more time. In many cases, however, a low-histamine diet should be followed until the underlying root cause of histamine intolerance is properly addressed and managed.