If you’re one of the 49 per cent of the UK population to suffer from hay fever, according to figures Allergy UK , you’ll be all too familiar with the concept of histamine – in fact, you’ve probably reached for the antihistamines on a regular basis to quell the runny nose and itchy eyes or to calm the itching after a mosquito bite. Releasing histamine (a neurotransmitter involved in immune response which also regulates certain functions in the gut, brain, spinal cord and uterus) is our body’s way of trying to protect itself from invaders but in the case of hay fever, this immune reaction goes into overdrive.
Now though, in an age where our immune systems have been challenged like never before, histamine issues are increasingly emerging as part of the many Long Covid symptoms people can experience. And a low histamine diet could help.
What is histamine and how is it linked to Covid?
Abnormally high levels of histamine now appear to be a factor in Long Covid, says Dr Tina Peers , a consultant doctor with a specialist interest in histamine intolerance (HI). She noticed that the symptoms of this condition were very similar to many Long Covid symptoms.
Histamine intolerance (more of which below) is a syndrome that occurs when the body is unable to break down histamine sufficiently and so we have too much of it in our bodies. It affects one in 100 people, but could affect up to five percent of the population according to the Histamine Intolerance Awareness campaign. It can be genetic, but other facts can trigger sensitivity too.
“Interestingly, all of my patients with Long Covid also have elevated histamine levels, not just those with histamine intolerance. We’re seeing a multitude of symptoms mainly based around inflammation in various different parts of their bodies,” says Dr Tina Peers .
“People can experience severe headaches , skin irritations, itchiness, hives, sinusitis, rhinitis, shortness of breath, dizziness and nausea, plus IBS -type symptoms including diarrhoea, constipation, bloating and abdominal pain. They can also experience extreme fatigue (ME), brain fog and neurological symptoms such as paints in their feet, face and tingling sensations in the body. This list isn’t exhaustive and varies from person to person.”
How could a low histamine diet help with Long Covid symptoms?
Dr Peers is having some profound results in treating high histamine levels with diet as certain foods can also contribute to our overall histamine load. “By reducing the histamine in people’s diet, we’ve been able to reduce many of their Long Covid symptoms.”
“This type of diet is difficult to follow but often people see an improvement very quickly – their itchy skin, fatigue, brain fog and IBS symptoms can all improve,” she explains. “The response of my patients depended on how severe their symptoms were. Some saw an improvement within a matter of days after reducing the histamine in their diet, but others took a few weeks.”
Why can Covid create too much histamine in the body even if you’ve never had an issue before?
It all comes down to a particular type of immune cells called mast cells, which are the body’s major histamine producers. In some people, mast cells seem to misfire after they have had Covid. Producing too much histamine can cause what’s known as Mast Cell Activation Syndrome or MCAS according to immunologist Dr Jenna Macciochi . “Scientists have been investigating the role of histamine in the development of MCAS,” she says.
However, MCAS doesn’t cause a ‘histamine intolerance’ as such, explains Dr Peers. “Anyone would react badly to having high levels of histamine in their body. Any virus, including the coronavirus, will cause a release in the histamine from mast cells,” she continues. “However, we think that if patients have dysfunctional mast cells then this response is exaggerated. The coronavirus seems to really exacerbate the condition.”
Dr Peers believes that 98 per cent of her Long Covid patients with histamine issues have a previous history of undiagnosed and untreated Mast Cell Activation Syndrome, in which histamine levels play a part.
“More and more clinicians are aware of this link and are treating patients accordingly,” she says.
So, what are mast cells? “Mast cells are a type of inflammatory cell and are found everywhere in the body, but particularly in the nasal passages, upper airways and lungs,” explains Professor Barbara Ryan, Consultant Gastroenterologist and co-founder of The Gut Experts.
“Mast cells release histamine and this in turn contributes to a cascade of inflammation that can develop during Covid-19 infection. It leads to a so-called ‘cytokine storm’, associated with severe infection. Cytokines are potent proteins involved in triggering and controlling the inflammatory response in the body to any invading infection, such as Covid-19, and they’re also involved in auto-immune conditions,” she continues. “The inflammatory response to Covid infection is very complex but mast cells are an important player.”
This theory seems to be confirmed by a small study that compared 13 adults with symptoms of Long Covid to asymptomatic Covid cases of a similar age. The 2021 study by Northwestern University Feinberg School of Medicine in the US, looked for mast cell mediators (chemicals produced when mast cells are activated) in Long Covid patients, some of which were significant and correlated with raised levels of inflammation. “This suggests that mast cells and histamine may be playing a role in Long Covid symptoms,” adds Professor Ryan.
What is a low histamine diet?
A normal, healthy diet contains moderate levels of histamine. Ordinarily, this doesn’t cause a problem. Certain foods such as strawberries , avocado and chocolate (except white chocolate) contain higher levels of histamine. If you are histamine intolerant, they can trigger any of the range of familiar symptoms from itchy eyes to rashes. Reducing or eliminating high-histamine foods, under the guidance of a dietician, can help alleviate symptoms, whether you have a histamine intolerance or histamine issues relating to Long Covid.
What are high-histamine foods?
- Alcohol such as wine and beer
- Fermented foods such as sauerkraut, kefir and kombucha
- Yeast extract or Marmite
- Dairy products such as yoghurt
- Foods that contain vinegar such as pickled vegetables
- Cured meats such as bacon and salami
- Soured foods such as sourdough bread, soured cream or buttermilk
- Aged food including cheeses like Blue, Roquefort and Parmesan
- Nuts and dried fruit (these may contain mould)
- Tomatoes, avocados, spinach and aubergines
What are low-histamine foods?
- Most fresh fruit (except citrus) and vegetables (except those below)
- Fresh meat, poultry and fish (except shellfish)
- Most fresh herbs and spices
- Dairy milk (assuming you don’t have a dairy intolerance)
- Gluten-free oats
- Dairy substitutes such as coconut milk
- Gluten-free grains such as quinoa and rice
- Olive oil
How you store and cook your food can increase its histamine content
If you love aged cheeses and you have a histamine intolerance, beware. Histamine levels in food increase with ‘maturation’ as in aged cheeses, cured or smoked meats and fish. Fermented foods and drinks such as sauerkraut and kefir are some of the worst offenders.
Research shows the longer food is left out the more histamine is produced – so the fresher your food the better. How you cook it has also been found to affect histamine content – steaming or braising, for example, have been shown to produce less histamine than grilling or frying.
Do antihistamines help with Long Covid?
Our experts agree it may be worth trying a low-histamine diet if you’re one of the 1.3 million people in the UK, battling long Covid . But while taking over-the-counter antihistamines may help with general histamine intolerance, expert opinion is divided over whether they could help if you develop Long Covid.
“Over-the-counter antihistamines aren’t officially recommended for Long Covid at the moment,” advises Professor Ryan, “but anecdotally, we know that some people are taking them, and depending on how the evidence evolves, they may be officially recommended further down the line.”
“Whether or not you have Long Covid, the important thing to do is speak to a doctor to confirm your issues aren't due to another condition that needs treating,” confirms Anna Mapson, Registered Nutritional Therapist at Goodness Me Nutrition . “It could be worth trialling a low histamine diet for a short while, but it's important to try and address the cause of the high histamine rather than avoiding too many foods. Women may find their histamine issues are worse around their period due to the effect of oestrogen on histamine levels.”
Could a low histamine diet be good for hay fever too?
Experts are divided, but most agree that a low histamine diet would be unlikely to help with hay fever as it’s an allergic reaction and not a histamine tolerance issue.
“Hay fever is caused by an allergy to triggers such as grass, pollen or house mites,” explains Professor Ryan. “This is caused by binding of the grass or pollen to IgE antibodies in the nasal passages and eyes. The binding of the particular trigger to the specific (allergic) IgE antibodies causes mast cells to be activated in the nasal passages and to release histamine locally in the nasal passages/airways. This has nothing to do with histamine in the diet and is a completely different mechanism.”
What exactly is histamine intolerance and can a low histamine diet help?
Histamine intolerance is thought to affect up to five per cent of people in the UK . A majority of those diagnosed are women in their 40s according to the Histamine Intolerance Awareness campaign . Dr Jenna Macciochi says histamine intolerance happens when there’s an imbalance between the build-up and breakdown of histamine. You may for example notice that you “lose the ability to tolerate histamine-rich or histamine-inducing foods,” explains Dr Macciochi.
If you have HI, symptoms can potentially occur at any time – they are not seasonal as with hay fever or an occasional allergic response to something in the air such as pet dander, say, triggered when you go into someone’s house who has cats.
Instead, they are caused by histamine found in foods and an inability to metabolise it properly. An enzyme known as diamine oxidase or DAO is responsible for clearing histamine from the body and some people, for various reasons, have a deficiency of it.
“Some people don’t break down histamine very well due to genetics and the composition of their gut microbiota,” says Dr Macciochi. “If this happens, histamine can start to affect normal body functions, leading to a host of unpleasant, and sometimes subtle, symptoms like headache, dizziness and hives’.
So, the theory is that by eating low histamine foods you reduce your body’s histamine levels and minimise the potentially unpleasant symptoms of histamine intolerance.
What are histamine intolerance symptoms?
“(HI) can be difficult to recognise as the symptoms can be non-specific and can mimic other conditions such as IBS or food allergy,” says Professor Ryan. “HI is often not on a doctor’s radar and so is often simply not considered.” She says if you develop the symptoms below after eating, you might consider the possibility of having a HI.
- Runny nose or watery eyes
- Tingling around the lips or tongue
- Flushing of the skin or the development of a rash, hives or itchiness after eating
- Shortness of breath related to eating
- Palpitations (racing heart)
- Dizziness or headaches
“These types of symptoms could also be caused by a food allergy, so it’s vital to rule out the possibility of a specific food allergy as this can be potentially life-threatening (someone might need to carry an adrenaline pen for example),” emphasises Professor Ryan. “Some of the digestive symptoms of HI can be similar to a number of digestive conditions including coeliac disease, IBS or even Inflammatory bowel disease (IBD, such as Crohn’s disease or colitis), so it is important that other conditions are also excluded.”
Which supplements can help with histamine intolerance?
Factors that make you more susceptible to HI include certain nutritional deficiencies, for example, vitamin B6 or zinc , according to Dr Sarah Brewer, GP and Medical Director of Healthspan. She says vitamin C has natural antihistamine properties and suggests taking a supplement (such as Healthspan Ester-C, £14.95) could help to break the histamine down. Pycgnogenol, a supplement made from pine bark extract, has also been shown to reduce histamine release – find it in Healthspan Pycgnogenol , £16.95. Nutritional therapist Alison Cullen recommends A.Vogel Stinging Nettle Urtica Drops , £10.85.
Is a low histamine diet healthy?
Critics point out it can be super restrictive and potentially put you at risk of nutritional deficiencies. Done carefully, however, there is nothing to stop it from being a healthy way of eating. “There are plenty of healthy vegetables, fruit, grains and proteins available to you on a low histamine diet,” says Alison Cullen. “However, it is not intended as a long-term diet plan.”
We interviewed further leading medical experts for this piece to ensure a balanced view. A big thank you to Daniel O'Shaughnessy, Director of The Naked Nutritionist and author of Naked Nutrition: An LGBTQ+ Guide To Diet and Lifestyle . Dr Jenna Macciochi’s new book Your Blueprint for Strong Immunity is out on 24th Feb.