Is Long Covid the result of an immune system that has failed to bounce back after a Covid-19 infection? How has the immune system been affected and what role does inflammation play? Do these problems share the same pathways as histamine intolerance? Could a low histamine diet influence Long Covid symptoms?
This short review will explore these questions and summarise the evidence on the relationship between the low histamine diet and Long Covid.
To explore the histamine in the context of Long Covid, lets first dive into what histamine is, and why some people choose to adopt a low histamine diet.
What is histamine?
Histamine is a chemical which plays many important roles throughout the body. In the immune system, it is used as a tool to help fight off threats. For example, in response to an insect bite, your immune system will initiate an inflammatory response around that bite, and you will experience redness, itchiness, and swelling. This is part of the normal inflammatory process, and histamine plays a key role in this.
Due to its important role in fighting off threats, it is vital that the level of histamine in our bodies remains stable. This is achieved by tightly regulating histamine production and breakdown. However, sometimes something may disrupt this balance, and too much histamine may end up in our system.
Histamine in food
Histamine can be found in nearly all of the foods we eat, and so when we sit down for a meal, our digestive system suddenly receives a large dose. If all this histamine entered our blood stream, it would disrupt the body’s delicate balance. Our digestive system therefore has a clever way to eliminate this dietary histamine and prevent it from being absorbed.
In the gut of a healthy person, an enzyme called Diamine Oxidase (DAO) acts to break down histamine from food. This prevents histamine being absorbed and thus the delicate balance is left untouched.
Histamine intolerance
When someone is unable to tolerate the amount of histamine offered by an average diet, they are said to have a histamine intolerance. There are a number of potential causes for this, and factors include genetics, gut health, diet, and medication. One of the ways these factors influence histamine tolerance is by affecting the activity of DAO. When DAO activity is reduced, less dietary histamine is broken down in the gut and more is absorbed.
In histamine intolerant individuals, cells all over the body are exposed to these higher-than-normal levels of histamine, a variety of symptoms may be experienced, ranging in severity from mild to severe. Symptoms include nausea, abdominal pain, constipation, dry or itchy skin, headaches, dizziness, congestion, fatigue, irregular menstrual cycles, and temperature regulation issues. Because histamine is so widely used throughout the body, symptoms can appear in a huge variety of different ways. The complex variability of these symptoms makes histamine intolerances very hard to diagnose.
Low histamine diet
An effective way to manage histamine intolerance is to avoid certain problematic foods. These are foods which tend to have higher levels of histamine. However, it’s important to note that there is no such thing as a histamine-free diet, as nearly all foods contain even small quantities. Also, there is no one definitive list of which foods are safe, and which aren’t. This is because there are so many factors that can influence the amount of histamine in any given food, such as processing method. Thankfully, there are some general patterns which can be followed…
Following such a dietary pattern can be very restrictive and can increase the risk of nutritional deficiency. Individuals looking to adopt this diet should therefore first consult a registered dietician or healthcare professional who be able to determine if this is the right course of action, and if so, help an individual adopt this diet smartly and safely.
Low histamine diet & Long Covid
Long Covid refers to the lasting and ongoing symptoms experienced by patients recovering from a Covid-19 infection. These symptoms may arise during or after the initial infection, and typically last from 4 to 12 weeks.
Long Covid symptoms can vary dramatically between people, both in symptom type and severity. Commonly reported symptoms include fatigue, shortness of breath, chest pain or tightness, brain fog, headaches, dizziness, abdominal pain, nausea, and loss of taste and smell. Scientists are yet to determine the exact cause of these symptoms.
Some scientists have considered whether the Covid-19 virus could be impacting a certain type of cell in our immune system called a mast cell. Mast cells are responsible for releasing histamine, and these scientists are investigating whether Covid-19 could be impacting how these cells function.
Symptoms of Long Covid are similar to those of histamine intolerance. Faulty mast cells and the resulting disruption to the balance of histamine might therefore explain why these symptoms overlap. This has led some people to ask whether following a low histamine diet could help those experiencing symptoms from Long Covid.
What does the evidence say?
From the available literature, there is not enough evidence to definitively say that Long Covid is the result of faulty mast cells. Similarly, there is not enough evidence to state whether following a low histamine diet will help reduce symptoms of Long Covid.
The restrictive nature of the low histamine diet, in combination with the often-debilitating symptoms of Long Covid, means that following such a diet has the potential to do more harm than good. It is therefore vital that anyone wishing to make any significant changes to their diet do so with the help of a registered dietician.
What DO we know?
What is clear, is that a number of both dietary and non-dietary lifestyle factors are important in the context of a low histamine diet, Covid-19 infection and Long Covid.
Individuals following a low histamine diet are advised to make additional, non-dietary changes to help manage the condition. High levels of stress can lead to increased histamine levels, as can sleep deprivation. Therefore, managing stress and getting sufficient quality sleep are therefore important in managing symptoms of histamine intolerance. Exercise also plays an important role in a healthy immune system.
There is also evidence showing that measures taken to prevent obesity and type II diabetes can reduce risk of viral infections, reduce symptom severity, and improve recovery. These measures include eating a heathy diet and getting plenty of physical activity. Whilst more research is needed in the context of Covid-19 and Long Covid, making these positive lifestyle changes can offer many benefits to overall health and wellbeing.
To learn more about eating well during your recovery from Covid-19, take a look at Your Covid Recovery from the NHS.
Summary:
The overlap of symptoms between histamine intolerance and Long Covid, as well as the suggestion of a histamine-related mechanism for Long Covid, have led some to wonder if a low histamine diet may benefit individuals suffering from Long Covid. However, there remains a great deal of uncertainty around Long Covid, its symptoms, and its treatment. As of yet, there is a lack of evidence to suggest that following a low histamine diet will be beneficial for those suffering from Long Covid. What is well understood, however, is the importance of lifestyle factors such as a healthy diet, good sleep, and physical activity in maintaining a healthy immune system and improving overall health. Many useful resources are available from the NHS for those looking to learn more about recovery from Covid-19.
Useful links and further reading:
Caution advised with low histamine diets for Long Covid – British Dietetic Association
The Food List – Histamine Intolerance Awareness
James PT, Ali Z, Armitage AE, et al., (2021) The Role of Nutrition in COVID-19 Susceptibility and Severity of Disease: A Systematic Review, The Journal of Nutrition, 151(7): 1854–1878
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