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‘Long-haul Covid’ or ‘Chronic-covid’ is now a well-recognised condition with an array of symptoms ranging from:


  • gut-related symptoms including diarrhoea and nausea
  • persistent fatigue (chronic fatigue and ME is being reported more)
  • persistent cough, headaches
  • brain fog
  • heart-palpitations
  • vascular dysfunction (link Covid-toes)
  • inflammatory-type pains
  • an increase in mood disorders

This list is not exhaustive and symptoms are usually still present after 4 weeks, frequently longer, in those who have recovered from the acute symptoms of the virus but are left feeling far from ‘right’, without any other seemingly logical or diagnosed explanation..

There is a lot that is not yet known as we are only discovering more as time goes on and different groups are studied.   Tim Spector, Professor of epidemiology at Kings College and leader of the Covid Symptom Survey App estimates around 300,000 people have been suffering symptoms over a month and in another recent pre-print study investigating the antibody response to SARS-CoV-2, the authors discovered 50% of their asymptomatic sample had persistent active virus in the small intestine 3-4 months after infection (Study).

There is a recognised pattern of individuals with eczema and asthma suffering more than others – the link here likely being that  SARS-COVI-2 is primarily is a respiratory infection.   However, the ACE2 receptors that the virus binds to are found in more places than just the lungs and this may be a link to some of the appearingly, far-reached symptoms that are seen.

Some hypothetical mechanisms that may be at play include:

  • Mast cell activation syndrome (MCAS)  (Afrin, 2020) – MCAS can affect multiple symptoms in the body at once, often causing a wide-range of debilitating and unpleasant symptoms.  Many symptoms can be similar to severe forms of histamine intolerance.  Interestingly and pertinently, mast cells (see below for more on what mast cells are) display ACE2 receptors which the SARS-COVI-2 virus dock onto.
  • Persistent viral infection – this can feed into MCAS so potentially inter-related mechanisms are at play and the role of persistent viral-infection in chronic fatigue and ME is well-established albeit not well understood, probably due to its multi-factorial and multi-system mechanisms.  From a functional perspective, an individual’s prior viral load, toxin load including environmental biotoxins such as mould, individual genetics along with nutrient status will all contribute to the likelihood of this being a risk factor.
  • Auto-immune mechanisms –  antibodies to serotonin and other potential auto-immune mechanisms have been discussed and there are some reports of those with rheumatoid arthritis suffering greater Long-covid symptoms.  Again, genetics and a pre-disposition to auto-immunity is likely to play a role here. Auto-immune conditions usually require a ‘trigger’ to be expressed and its feasible that the SARS-COVI-2 virus may be a trigged for some.

So what are mast cells?   Mast cells are a certain types of red blood cell that are loaded with histamine which are released in response to certain inflammatory triggers.  They are an integral part of our immune system.    As I mentioned, mast cells also express ACE2 receptors which we know is the principal receptor for SARS-COVI-2.  Potentially could this make mast cells a receptor of the virus?   A theory proposed by Theoharides, 2020. 


Mast cells also provide a critical link between the immune and nervous systems – one the reasons MCAS can display such a wide array of symptoms, including many neurological ones listed above.    Their basic function is to deal infections agents (such as viruses) and toxins and they do this in part by releasing histamine which is responsible for the heat and hive-type reaction you may get on your body if you touch something that irritates the skin.

When a mast cell is constantly stimulated with signals, they can lose their specificity and begin to react to ordinary stimuli and result in a host of ‘strange’ unwanted responses and often client’s may present with multiple sensitivities and often no clear pattern can be noted.   Note this is not the same as an allergic response.  

Interestingly, mast cells can store thyroid hormone (T3) and express certain thyroid hormone receptors (TSHRs), suggesting two things:  firstly thyroid dysfunction may be a risk factor for Long-covid  or secondly that Long-Covid and activated mast cells may impact thyroid function (Ref).

A final connection for now is that of oestrogen, progesterone and histamine – histamine-type symptoms are often worse at points in the cycle where oestrogen is high and unopposed by progesterone.  If you are a female and notice increased symptoms at certain times in your cycle, this is a further clue this mechanism is at play.

Enough of the science: what you can do:


  • Reduce histamine load in the body – diet is a short-term tool here as ideally you want to work on root causes and avoid long-term restriction but it can be a powerful one.   If you imagine a bucket (your mast cells) and your bucket of histamine is over-flowing.  By reducing what is put in the bucket will help you manage the outflow and slow it down and thus reduce symptoms.   Foods that are higher in histamine include left-overs. fermented foods, smoked foods, tinned foods and aged cheeses (this list is not exhaustive).  There are also certain foods that can inhibit the DAO enzyme which may also need to be limited and these include green and black tea and alcohol.
  • Support histamine breakdown and production – there are two main pathways for histamine breakdown and genetics plays an important role in how well each works.  Individualising requirements for key nutrients such as B6, vitamin C, quercitin and methylation nutrients (B6, B12, folate, magnesium) can all help*.   You can supplement with an enzyme known as DAO (diamine oxidase) which may help some people*.    Genetic testing of key SNP’s in the histamine pathway can be very useful to understand where your susceptibilities lie.
  • Work out what is causing the trigger of histamine from the mast cells beyond SARS-COVI-2 – what has made you susceptible to this virus and Long-covid in the first place?   This usually involves working along your time-line with a qualified practitioner and understanding your genetics in more detail and maybe some functional blood testing.
  • Ensure adequate anti-viral nutrient support (ie appropriate immune system support) which can include zinc, vitamin A, D, C and E.  Evidence for higher dosing of vitamin C during an active viral infection is wide-spread and it is now well-established that being deficient in vitamin D can increase mortality from Covid-19 *.
  • Support the gut –  the DAO enzyme mentioned above is produced in the gut so any conditions such as SIBO, Celiac Disease, other gluten sensitivities or intolerances, and Crohns Disease that can impact the structure and function of the micro-villi may impact its function and thus histamine load and tolerance.  Minimising processed foods including gluten, avoiding alcohol and NSAID use is recommended.   Include plenty of mucilaginous herbs such as okra and chia, and short chain fatty acids such as butyrate (ghee and cold, boiled potatoes).
  • Include plenty of anti-inflammatory herbs and spices such as curcumin, rosemary and oregano and other supportive foods include mushrooms high in beta-glucans and elderberry may help.
  • Be careful with foods higher in sulphur such as garlic, onions, kale, brassicas and leeks where MCAS and histamine are playing a role as often the sulphur metabolism pathway is impacted.

* Please note that none of the above are intended as recommendations but for education only and supplement advise should always be followed under the advise of a suitably qualified professional.  Drug nutrient interactions should always be considered along with biochemical individuality.

Katherine is a degree qualified Nutritional Therapist (BSc First Class, Nutritional Science) working with a wide-array of clients, with a specific interest in working with complex chronic conditions, anyone who loves their sport and eating disorders.  She also works with clients suffering from cancer, specifically Breast Cancer and Prostate Cancer.

She has additional training in Eating Disorders from the National Centre for Eating Disorders, is a NLP Practitioner, has trained in EFT (Emotional Freedom Technique) and as well as carrying out 1-2-1’s with clients, lectures on Gut Dysfunction and Functional Testing in Athletes for the Centre for Integrated Sports Nutrition.

To find out more how Katherine can help you please contact her on