Constant tiredness is often easily dismissed as the result of late nights (Image: Maria Korneeva via Getty Images)
Constant tiredness is often easily dismissed as the result of late nights, after-work drinks, or dehydration. We also commonly blame the weather at this time of year. Less sunlight and adverse weather conditions can disrupt our circadian rhythm, leading to reduced activity and increased fatigue.
However, exhaustion is not the same as feeling tired and can actually be a sign of an underlying health problem. Over the years, I often brushed off tiredness, blaming everything and anything. However, a routine blood test showed that I was suffering from a B12 or folate deficiency. My ulcerative colitis likely caused the deficiency, as it often restricts my diet and prevents me from getting key vitamins and minerals.
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Other causes of B12 deficiency include a plant-based diet that lacks B12-fortified foods, a poor appetite, impaired absorption, and certain medications.
What are the symptoms of a B12 deficiency?
One of the main symptoms of this deficiency is extreme tiredness, but I also experienced breathlessness and memory problems. GP Dr Jeff Foster, who is the medical director of Voy, a UK-based online health service, said: “Vitamin B12 deficiency can show up in a range of physical and neurological symptoms, as it affects basically all of our nervous system. Common signs include persistent tiredness, weakness, breathlessness, headaches, pale or slightly yellow skin, a sore or smooth tongue, mouth ulcers, and pins and needles in the hands or feet. It is this final one that is the classic symptom of someone we look for in someone with seriously low B12. It is known as a glove and stocking neuropathy.
“Some people also notice problems with memory, concentration or low mood, and in more serious or long-standing cases it can affect balance and nerve function.”
Women’s health and hormone expert Dr Shirin Lakhani said a B12 deficiency is quite a common problem, especially in women. She added: “Signs to look out for include a lack of energy and a feeling of weakness, pale or jaundiced skin, mouth issues such as a red, sore tongue and mouth ulcers, memory and balance issues, pins and needles, and even depression and mood swings.”
Dr Tamsin Lewis said she saw several patients when she was working as a psychiatrist with what looked like mental health or neurodegenerative conditions, only to discover they had a B12 deficiency.
She said: “One case in particular really stuck with me: a patient with profound low mood, memory problems, and loss of executive function, raising genuine concern about a neurodegenerative condition. Once their previously unrecognised B12 deficiency was treated, their mood and cognitive symptoms improved dramatically. It was a striking reminder that some very frightening presentations can have reversible biological causes.”
One of the main symptoms of this deficiency is extreme tiredness (Image: Wasana Kunpol via Getty Images)
What causes a B12 deficiency?
Some of the primary causes of a vitamin B12 deficiency include inadequate dietary intake, impaired absorption in the gut, and the effects of certain medications or underlying medical conditions.
Nasir Ali, a clinically trained pharmacist, advanced practitioner and independent prescriber, said absorption problems, medications, not getting enough B12 from your diet and ageing and alcohol misuse can all cause a B12 deficiency to develop.
Mr Ali said: “A common cause is low dietary intake, particularly with vegan or largely plant-based diets that do not regularly include fortified foods or supplements. Absorption problems are also important, including pernicious anaemia where intrinsic factor is lacking, gut conditions such as coeliac or Crohn’s disease, or previous stomach or bariatric surgery.
“Medications play a role too, with metformin and long-term use of proton pump inhibitors or H2 blockers reducing B12 levels over time, alongside ageing, heavy alcohol intake, and nitrous oxide misuse, which can inactivate B12 and damage nerves. Often, it is a combination of reduced intake and impaired absorption, so identifying the main driver helps guide treatment.”
Dr Angela Rai, a GP at The London General Practice, agreed but added that older adults may absorb less B12.
However, Dr Tina Ghela, a Medichecks digital clinician, said the most common cause of vitamin B12 deficiency is an autoimmune disease called pernicious anaemia. She added, “This condition causes the body to produce an antibody that attacks the protein responsible for extracting vitamin B12 from food.”
She also stated that people taking metformin are at a greater risk of developing a vitamin B12 deficiency, and those taking the medication long-term are now recommended to be screened for a B12 deficiency, according to new Government guidelines.
She also agreed with Dr Rai that older adults are more at risk, especially those over the age of 60. She said: “It is thought that up to one in five people over the age of 60 may be affected by a B12 deficiency due to the decline in absorption rates as you get older.”
Foods of animal origin are the richest sources of vitamin B12 (Image: MEDITERRANEAN via Getty Images)
How to avoid developing a B12 deficiency
Preventing a vitamin B12 deficiency involves a combination of factors. Ensuring an adequate dietary intake, using supplements and managing risk factors are all important.
Foods to eat to avoid B12 deficiency
Mr Ali recommended building meals around sources of B12, including meat, fish, shellfish, dairy and eggs. If you follow a plant-based diet, he recommended eating fortified plant milks, breakfast cereals and nutritional yeast consistently.
Dr Martin Thornton, chief medical officer at Bluecrest, agreed, adding: “Foods of animal origin are the richest sources of vitamin B12, so try to include plenty of foods such as beef, liver, poultry, fish, shellfish, eggs, and dairy products in your diet.
“For people following a vegetarian diet or vegan diet, some plant-based foods are fortified with vitamin B12. Look for fortified cereals, plant-based milk alternatives, nutritional yeast, and meat substitutes.”
Dr Max Gowland, a leading UK biochemist with over 30 years’ experience in nutrition and health science, agreed that animal-derived foods are some of the best sources of B12. He explained: “Rich sources include meat, fish, shellfish, eggs and dairy products. Liver and shellfish are particularly high in B12, although not everyone enjoys eating them regularly.
“Plant foods do not naturally contain meaningful amounts of B12, unless they are fortified. Some breakfast cereals, plant milks and nutritional yeasts are fortified and can contribute to intake, but levels vary widely. For people relying on fortified foods, consistency matters, as occasional intake is unlikely to be enough.”
Supplements
Dr Gowland also said that for some people, supplementation is the most practical and effective way to maintain healthy B12 levels, especially for vegans, older adults and those with absorption issues.
He said: “Oral B12 supplements can be absorbed by passive diffusion, bypassing some of the normal absorption steps. This means they can still be effective even when stomach acid or intrinsic factor is reduced. In more severe cases, or where absorption is very poor, regular B12 injections may be prescribed under medical supervision.
Over the years, I often brushed off tiredness, blaming everything and anything for it (Image: Maria Korneeva via Getty Images)
“A recent analysis of prescriptions in 2024 shows that in the UK, around five million vitamin B12 prescriptions, both supplements and injections, were made, demonstrating how common B12 deficiency really is. Clearly, supplementation is a low-cost and effective way of ensuring our B12 levels stay healthy.”
Mr Ali said those who are vegan or mainly plant-based should add a dedicated B12 supplement to their diet. He recommended at least 10mg daily or around 2000 micrograms once a week.
Dr Lewis said the impact of taking a B12 supplement can be “huge” if it’s taken properly. She said: “Although B12 is found in meat, fish, eggs, and dairy, many people simply can’t absorb it properly through the gut. In those cases, B12 injections or high-dose sublingual B12 (absorbed under the tongue) are used because they bypass the digestive system altogether – and when done properly, the impact can be huge.”
What should you do if you suspect you have a B12 deficiency?
If you suspect you have a B12 deficiency, the experts recommend consulting a medical professional like your GP. It’s especially important to speak with them if you are experiencing symptoms or if you belong to a high-risk group.
A B12 deficiency is diagnosed through a blood test, with the experts suggesting you request a full blood count and a serum B12 test.
However, Dr Ghela notes that measuring the level of active B12 can be more accurate than measuring the total B12, as sometimes measuring the total level can give misleading results.
Dr Ghela explained: “It is important to note that only active vitamin B12 can be used in the body, so measuring the total level of B12 could give misleading results and fail to diagnose a deficiency.
For mild cases, the treatment plan is likely to include oral B12 supplements and some dietary adjustments (Image: Galina Zhigalova via Getty Images)
“For example, even if the results showed a normal range of vitamin B12 in the blood, the levels of useful active B12 could still be low.”
Tobias Mapulanga, a biomedical scientist from Repose Healthcare specialising in haematology, immunology and diagnostics, added that if the symptoms fit but the results are borderline, you should request methylmalonic acid or homocysteine for clarification.
What is the treatment for B12 deficiency?
Based on your blood test results and the severity of the deficiency, your doctor will develop a suitable treatment plan for you. For mild cases, the treatment plan typically includes oral B12 supplements and some dietary adjustments.
However, for cases where the patient has malabsorption, such as pernicious anaemia, B12 injections or a high-dose sublingual B12, which bypasses the gut, may be needed.
If a B12 deficiency is caught early, it’s possible to restore levels through supplements and dietary changes alone. If you’re experiencing symptoms of a B12 deficiency, it’s essential to consult your GP and request a blood test.
Dr Lewis concluded: “If there’s one takeaway I’d love people to have, it’s this: if symptoms don’t quite add up, think B12. It’s an easy thing to test, but missing it can have life-changing consequences – while spotting it can be genuinely transformative.”
