My Pain and Low Energy Turned Out to Be Symptoms of an Autoimmune Disease

For a decade, Claire Lynch was prescribed heartburn medication for persistent stomach pain, headaches and a lack of energy.

Doctors diagnosed her with chronic gastritis and several other digestive conditions. However, after consultations with five gastroenterologists, her symptoms continued without relief.

The eventual explanation was autoimmune gastritis — the same condition affecting US biohacker and longevity influencer Bryan Johnson.

The disease affects an estimated 500,000 people in the UK. It develops when the immune system attacks the stomach lining, reducing stomach acid and often causing deficiencies in vitamin B12 and iron.

Symptoms can include extreme tiredness, anaemia and neurological problems such as pins and needles, changes in mood and poor balance. If the condition goes untreated, it may cause permanent nerve damage. Some patients develop memory problems or become more likely to fall, while in rare cases they can eventually require a wheelchair. Although uncommon, autoimmune gastritis may also raise the risk of stomach cancer.

Yet the condition is frequently overlooked, leaving patients to cope with debilitating symptoms for years. When it is identified early, however, treatment can often be straightforward, with vitamin injections helping to correct deficiencies.

Claire recalls that her health problems began in 2005, when she developed abdominal pain, bloating, persistent headaches, joint pain and fatigue.

She was in her 40s and working for a bank in the City of London. As gluten-free diets were becoming widely discussed, she decided to try one herself. Within a few months, many of her symptoms appeared to have eased.

In 2011, a course of antibiotics prescribed after a tooth infection led to severe diarrhoea and stomach cramps. Over the following two months, Claire lost around a stone and a half.

“I saw a doctor who advised me to try probiotics, but they made no difference, so he referred me to a gastroenterologist,” she says.

A month later, Claire underwent a colonoscopy, during which a small camera was used to examine her colon. The procedure revealed collagenous colitis, an inflammatory bowel disease that can cause ongoing watery diarrhoea and weight loss. It is also an autoimmune condition.

“I was treated with steroids, which cleared up the colitis, but another blood test showed I had anti-parietal gastric cell antibodies,” she says.

These antibodies wrongly target parietal cells in the stomach lining. Those cells produce stomach acid as well as intrinsic factor, a protein needed to absorb vitamin B12 — a nutrient vital to healthy nerves and the production of red blood cells. Although such antibodies commonly lead to B12 deficiency, Claire’s levels were normal at first.

By 2016, Claire continued to experience stomach pain and nausea, and had begun belching frequently. An endoscopy suggested bile reflux, in which digestive fluid travels back up from the intestine. A medication intended to speed up digestion appeared to help for two years, but it was later withdrawn because of adverse effects. Claire was then moved on to acid-reflux treatment.

“I remembered the anti-parietal antibodies and asked whether they could be causing low stomach acid, but the possibility was dismissed. Nobody joined the pieces together,” she says.

It was not until December last year — after consultations with four more gastroenterologists and almost 20 years since her symptoms first appeared — that Claire finally received diagnoses of autoimmune gastritis and pernicious anaemia. The latter is another autoimmune disease that attacks parietal cells and can reduce levels of intrinsic factor.

Experts estimate that about two million people have vitamin B12 deficiency, which is commonly associated with autoimmune gastritis or pernicious anaemia.

Autoimmune gastritis is more frequently seen in women, “as is true of most autoimmune conditions,” says Dr Jason Dunn, a consultant gastroenterologist at Guy’s & St Thomas’ Hospitals NHS Foundation Trust and Welbeck private clinic, both in London.

‘It’s also more common when you have other autoimmune conditions, such as type 1 diabetes.

‘Your risk also increases with age.’

Unfortunately, as Claire discovered, the vague symptoms mean diagnosis can take a long time, explains Dr Andrew Klein, a consultant anaesthetist at Nuffield Health Cambridge Hospital and Royal Papworth Hospital in Cambridge – who has a special interest in anaemia and is conducting research into iron deficiency treatment.

Symptoms of autoimmune gastritis and B12 deficiency are subtle, he adds.

‘You start feeling a bit tired, your memory and concentration go a bit, then you start to get tingling and pins and needles in the fingers.

‘Next you get patches of numbness as if you have gloves or socks on – then become unsteady on the feet or finding it difficult to open a jam jar or a door. You can get sore or swollen tongue, sore gums and vision problems.’

With the nerve-related sign, ‘there are lots of different symptoms; in teenagers and young people it’s more anxiety and hallucinations, and in older people it can be memory loss’.

It takes on average five to ten years to get a diagnosis, adds Dr Klein, who also runs Cambridge Iron and B12, a private clinic specialising in looking after patients with B12 and iron deficiency.

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The inaccuracy of B12 blood tests can be a factor.

As Dr Klein explains: ‘If there are any B vitamins in your diet – Marmite, breakfast cereals and oat milk, for instance, all have added B vitamins, as do multivitamins and other supplements – this can skew the results: they overestimate the levels.’

He says patients must stop taking any B vitamin supplements or eating food with added B vitamins three months before a test.

‘Other more sensitive tests – known as homocysteine and MMA – are available,’ he adds.

Not everyone with autoimmune gastritis will go on to get pernicious anaemia, explains Dr Dunn. ‘If it is very mild and just affected a very small part of the stomach, for example. As well as B12 deficiency, iron deficiency can be associated with autoimmune gastritis.’

It was actually low iron levels that pointed to the real problem for Claire. By November 2024 her regular annual blood test at the GP showed that her B12 was normal, but iron stores (known as ferritin) levels had dropped.

Claire’s symptoms were getting worse, too. ‘In addition to the ongoing tummy pain and nausea, I developed pins and needles, dizziness and numbness in my hands and feet,’ she says.

‘I was becoming quite fatigued and breathless during my afternoon walks with my dog, Harry.

‘I was also coughing, mostly during the night, and had a burning sensation in my feet – and having once been able to do fairly long runs, I could now only run in first gear for short distances.

‘I also had a strange feeling of irritation/anger, which is not like me at all.’

Claire’s husband Kevin, 66, was concerned about the coughing, so she saw her GP who agreed with the previous diagnoses of bile reflux and thought her cough could be due to stomach acid reflux.

‘My concern about the low ferritin and dropping B12 levels was dismissed,’ says Claire. She was prescribed a proton pump inhibitor (PPI), lansoprazole, for the acid reflux for a month, ‘which did nothing, in fact, made me feel worse’.

Last year, after her annual blood test again showed her iron levels were still abnormally low, she saw a fourth gastroenterologist, who gave her a gastroscopy – where a small camera is passed into the stomach via the mouth – and diagnosed chronic gastritis and prescribed more PPIs. This time Claire refused.

‘I told him I had gastric pain not acid reflux – but again my concerns were dismissed,’ she says.

Claire then began researching online and came across the Pernicious Anaemia Society – and discovered her real problem might be autoimmune gastritis.

Despite raising this with her GP and a fifth gastroenterologist, she was given yet another colonoscopy and PPIs.

Only when she received results of further B12 and iron tests – which showed both had fallen – was she seen by a sixth gastroenterologist, who specialised in iron deficiency anaemia and confirmed the correct diagnosis: autoimmune gastritis and pernicious anaemia.

Claire recalls: ‘She was wonderful – she didn’t fob me off, didn’t try to make me take more PPIs. She looked at my history and gave me the diagnosis.’

After just two weeks of treatment with vitamin B12 injections, the dizziness had gone and the fatigue had improved considerably.

It took ‘about a further four months for the numbness in my feet and pins and needles to resolve’. She will need to take the jabs (which she has every two months) for life. She is also now on iron supplements – she’ll be on this regimen for life.

After nearly 20 years of symptoms, Claire knows she’s been lucky.

Dr Klein says: ‘Neurological symptoms can become permanent as the nerves get damaged from the B12 deficiency and it is very often misdiagnosed as multiple sclerosis, depression, dementia. But if it’s treated early enough it is reversible.’

Claire, now 63, is feeling more optimistic about the future.

‘I feel much better but still feel I am running in first gear and don’t have the energy I did – but I am glad to have a diagnosis.

‘I feel vindicated after years of being fobbed off.’

• pernicious-anaemia-society.org