I suffered from stomach pain, headaches and low energy for ten years. Doctors tried everything… until tests revealed I had an autoimmune condition that affects thousands – and was helped with a simple vitamin jab

For ten years Claire Lynch took heartburn pills prescribed for her stomach pain, headaches and low energy. 

She was told she had chronic gastritis and various other digestive problems, yet despite seeing five gastroenterologists over that time, her symptoms never improved.

And with good reason. It turns out that Claire actually has autoimmune gastritis – the same condition as the US bio-hacker and longevity influencer, Bryan Johnson.

It affects around 500,000 people in the UK and occurs when the immune system attacks the stomach lining, which reduces the levels of stomach acid, in turn often leading to vitamin B12 and iron deficiencies.

It can cause a range of symptoms including fatigue, neurological issues (such as pins and needles, mood changes and poor balance) and anaemia. Left undiagnosed it can lead to permanent nerve damage – some people become prone to falling or suffer memory loss, or in rare cases end up wheelchair-bound. Although also rare, it can increase the risk of stomach cancer.

But unfortunately the condition is often missed – leading to patients suffering years of crippling symptoms. Yet if the condition is caught soon enough, it can often be resolved – by simple vitamin injections.

Claire says her symptoms began back in 2005 when she started to suffer with stomach pain, bloating, chronic headaches, joint pain and fatigue.

At the time – then in her 40s, she was working at a bank in the City of London – she says ‘everyone was talking about gluten-free diets’, so she tried it. And within months, many of her symptoms seemed to vanish.

But in 2011, after a tooth infection, she took antibiotics which triggered severe diarrhoea and cramping. After two months she had lost around a stone and a half in weight.

‘I saw a doctor who told me to try probiotics, which didn’t work, so he referred me to a gastroenterologist.’

A month later Claire had a colonoscopy, where a tiny camera is inserted into the colon, which showed she had a form of collagenous colitis – an inflammatory bowel disease that causes chronic, watery diarrhoea and weight loss. It is a type of autoimmune disease.

‘I was given steroids, which cured the colitis, but another blood test showed I had anti-parietal gastric cell antibodies.’

These antibodies mistakenly attack the parietal cells lining the stomach wall, which are responsible for producing stomach acid and intrinsic factor, a protein essential for absorbing vitamin B12 – important for healthy nerves and the formation of red blood cells. Typically these antibodies would cause B12 deficiency but Claire’s levels were initially normal.

A year later, in 2016, she still had stomach pains, nausea and had also started frequently belching; at this point an endoscopy suggested she had bile reflux (where digestive fluid backs up from the intestine). She was prescribed a drug to speed up the digestive process, which seemed to work for two years, but the drug was removed from the market due to adverse effects and Claire was switched to medication for acid reflux.

‘Remembering the anti-parietal antibodies, I asked if that could be causing low stomach acid, but it was dismissed – nobody connected the dots,’ she says.

It was only December last year, after seeing a further four gastroenterologists – and almost 20 years after she first developed symptoms – that she was finally diagnosed with autoimmune gastritis and pernicious anaemia – another autoimmune condition which also attacks the parietal cells, affecting intrinsic factor levels.

Around two million people suffer from B12 deficiency, and typically it’s linked to autoimmune gastritis or pernicious anaemia, say experts.

Autoimmune gastritis is more common in women ‘as is true of most autoimmune conditions’, explains 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.

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