Vitamin B12 Deficiency: Signs, Causes, Food Sources
Key Takeaways
- Vitamin B12 helps make red blood cells, keeps the nervous system healthy, and supports DNA synthesis, according to the U.S. National Institutes of Health (NIH).
- The recommended daily amount for most adults is 2.4 micrograms, rising to 2.6 micrograms in pregnancy and 2.8 micrograms while breastfeeding (NIH Office of Dietary Supplements).
- Risk is higher in older adults, people who eat little or no animal foods, people with pernicious anaemia, people who have had stomach or intestinal surgery, and people with conditions that affect absorption.
- Commonly listed signs include extreme tiredness, a sore red tongue, pins and needles, and changes in memory or mood — but these symptoms have many possible causes and are not a self-diagnosis checklist.
- B12 is found naturally in animal foods such as meat, fish, eggs, and dairy, and in fortified foods such as breakfast cereals and nutritional yeast.
Introduction
Vitamin B12 is a small nutrient with outsized responsibilities. You need only micrograms of it each day, yet it plays a central role in making red blood cells, maintaining healthy nerve cells, and supporting the production of DNA. Because the body stores B12 and uses it slowly, a deficiency often develops gradually — and its early signs, such as tiredness, are easy to attribute to a busy life.
This article explains what vitamin B12 does, who is more likely to run low, which signs are commonly listed by health authorities, where to find B12 in food, and when it is time to talk to a healthcare professional. It is general information only, not a diagnostic tool: many of the signs below overlap with other conditions, and only a blood test arranged by a clinician can establish whether B12 is actually low.
What Vitamin B12 Does in the Body
Vitamin B12, also called cobalamin, is a water-soluble vitamin. The NIH Office of Dietary Supplements (ODS) describes its key roles: it is needed for the formation of red blood cells, for neurological function, and for DNA synthesis. It also works with folate in processes that keep the nervous system healthy (NIH ODS, https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/).
Red blood cells carry oxygen around the body using haemoglobin. When B12 is lacking, the body produces abnormally large red blood cells that cannot function properly — the medical term for this is megaloblastic anaemia, as described by the UK's National Health Service (NHS). Because red blood cells and nerve cells are both affected, B12 deficiency can produce a wide mix of symptoms, from tiredness to nerve and mood changes (NHS, https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/?origin=serp_auto).
How Much Do You Need?
The NIH Office of Dietary Supplements sets the following recommended dietary allowances:
| Group | Recommended daily amount |
|---|---|
| Adults aged 14 and over | 2.4 micrograms (mcg) |
| Pregnant women | 2.6 mcg |
| Breastfeeding women | 2.8 mcg |
| Children aged 1–3 years | 0.9 mcg |
| Children aged 4–8 years | 1.2 mcg |
| Children aged 9–13 years | 1.8 mcg |
No upper intake level has been established for vitamin B12, because the available evidence has not identified a level at which adverse effects occur — a point the NIH ODS fact sheet makes explicitly. That does not mean large supplement doses are advisable without guidance; it means B12 from food is not a toxicity concern at ordinary intakes (NIH ODS, https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/).
The body absorbs B12 with the help of intrinsic factor, a protein made in the stomach, and stores it mainly in the liver. Because stores can last for some time, deficiency usually develops slowly, over months or years, rather than days.
Who Is at Higher Risk?
Anyone can develop low B12, but health authorities consistently name the same higher-risk groups. The NHS and the NIH ODS point to:
- Older adults. Both B12 and folate deficiency become more common with age, partly because the stomach produces less acid, which makes it harder to release B12 from food.
- People who eat little or no animal foods. B12 is naturally found in animal products, so people following vegan diets — and some vegetarians — need dependable fortified foods or supplements, as the NIH ODS advises. Plant foods do not naturally contain B12 in reliable amounts.
- People with pernicious anaemia. In this autoimmune condition, the immune system attacks cells in the stomach that produce intrinsic factor, so B12 cannot be absorbed properly even when intake is adequate.
- People who have had stomach or intestinal surgery. Procedures such as gastric bypass or removal of part of the stomach or small intestine can reduce absorption.
- People with digestive conditions that affect absorption. Coeliac disease, Crohn's disease, and chronic inflammation of the stomach lining (atrophic gastritis) are among the conditions named in clinical guidance.
- People taking certain medicines long-term. Clinical guidance from NHS hospital services lists medicines that can interfere with B12 absorption, including the diabetes medicine metformin and acid-reducing medicines such as proton pump inhibitors (PPIs) and H2 receptor blockers.
If you belong to one of these groups, it is worth being aware of the signs below — not to self-diagnose, but to know when a conversation with a clinician is warranted.
Commonly Listed Signs
The NHS lists a wide range of possible symptoms of vitamin B12 or folate deficiency anaemia, and stresses that they usually develop gradually but can worsen if the condition goes untreated. The list below follows the NHS grouping and is provided as general information only — it is not a checklist for self-diagnosis, because every symptom here has other possible causes too.
Energy and blood-related signs: extreme tiredness and a lack of energy, breathlessness, headaches, palpitations, and pale or slightly yellow skin. These reflect anaemia — fewer healthy red blood cells carrying oxygen.
Mouth and digestive signs: a sore and red tongue (sometimes called glossitis), mouth ulcers, loss of appetite, indigestion, diarrhoea, and weight loss.
Nerve-related signs: pins and needles (paraesthesia), numbness, muscle weakness, problems with balance and coordination, and disturbed vision. The NHS notes that some of these problems can be irreversible if deficiency is left untreated for a long time, which is why early diagnosis matters.
Thinking and mood signs: problems with memory, understanding, and judgement, irritability, low mood, and in more severe cases confusion. The NHS lists psychological problems ranging from mild depression or anxiety to confusion and dementia among the possible neurological symptoms.
One important nuance: some of these symptoms can occur in people who have a B12 deficiency but have not developed anaemia. A normal blood count therefore does not always rule out low B12, and clinicians may check B12 levels directly when symptoms and risk factors point that way. Conversely, tiredness alone is almost never enough to conclude anything — fatigue has many causes, from poor sleep and stress to thyroid problems and iron deficiency.
Food Sources of Vitamin B12
Vitamin B12 occurs naturally in foods of animal origin. The NIH ODS lists the following selected food sources, with values that may vary by product and preparation:
| Food | Serving | Vitamin B12 |
|---|---|---|
| Clams, cooked | 3 ounces | 84.1 mcg |
| Beef liver, cooked | 3 ounces | 70.7 mcg |
| Trout, rainbow, wild, cooked | 3 ounces | 5.4 mcg |
| Salmon, sockeye, cooked | 3 ounces | 4.8 mcg |
| Tuna, light, canned in water | 3 ounces | 2.5 mcg |
| Milk, low-fat | 1 cup | 1.2 mcg |
| Yogurt, fruit, low-fat | 8 ounces | 1.1 mcg |
| Egg, whole, cooked | 1 large | 0.5 mcg |
Source: NIH Office of Dietary Supplements (https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/).
For people who avoid animal products, fortified foods are the main dietary route. Fortified breakfast cereals are a readily available source with high bioavailability, according to the NIH ODS, and some nutritional yeast products also contain added B12 — but formulations vary, so it is important to read labels to confirm which nutrients a product actually contains. Unfortified plant foods, including mushrooms, seaweed, and fermented foods, should not be relied upon as a sole source, because their B12 content and biological availability are unreliable.
A practical note: B12 in fortified foods and supplements is not bound to protein, so it is absorbed differently from B12 in meat or dairy. That is one reason fortified foods and supplements are often suggested for older adults and for people taking acid-reducing medicines, whose stomach acid may not release food-bound B12 efficiently.
When to Talk to a Healthcare Professional
The NHS advises seeing a GP if you think you may have a vitamin B12 or folate deficiency, and notes that these conditions can often be diagnosed based on symptoms and the results of a blood test (NHS, https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/?origin=serp_auto). Seek medical advice promptly if you notice:
- Persistent, unexplained tiredness or weakness that does not improve with rest.
- New pins and needles, numbness, balance problems, or changes in how you walk.
- A persistently sore, red tongue or recurring mouth ulcers.
- Memory, concentration, or mood changes that are new or worsening.
- Any combination of the signs above, especially if you belong to a higher-risk group.
Do not start high-dose supplements on the basis of an online list. Supplements taken before testing can complicate diagnosis, and the underlying cause — such as pernicious anaemia or a digestive condition — still needs identifying. A clinician can order the right tests and recommend treatment appropriate to the cause, which may involve dietary changes, oral supplements, or injections depending on the situation.
Frequently Asked Questions
Can you have low B12 without anaemia?
Yes. The NHS notes that some symptoms of B12 deficiency, including nerve and thinking symptoms, can occur even when anaemia has not developed. That is why symptoms plus risk factors, not a blood count alone, guide clinicians toward testing.
Is tiredness always a sign of low B12?
No. Fatigue has many causes, including poor sleep, stress, thyroid disorders, iron deficiency, and depression. Ongoing tiredness is a reason to discuss testing with a healthcare professional, especially if other listed signs or risk factors are present — not a reason to conclude B12 is the cause.
Do vegetarians and vegans always need a B12 supplement?
Not always, but the NIH ODS advises that people following vegan diets obtain B12 from dependable fortified foods or supplements, because plant foods do not naturally provide it in reliable amounts. Vegetarians who eat dairy and eggs can obtain B12 from those foods, but intake varies, so it is worth checking dietary adequacy with a clinician or dietitian.
Can cooking destroy vitamin B12 in food?
B12 is relatively stable during ordinary cooking, though some is lost into cooking liquid. The bigger absorption issue is not cooking but the body's ability to release B12 from food and absorb it — which is why older adults and people with low stomach acid may still run low despite eating B12-containing foods.
How is B12 deficiency diagnosed?
Typically through symptoms plus blood tests. The NHS explains that diagnosis is often based on symptoms and blood test results, which may include haemoglobin, red blood cell size, B12, and folate levels. Additional tests are sometimes needed to find the underlying cause.
Medical Disclaimer
This article is for general information only and is not medical advice. Talk to a healthcare professional about your own situation, especially before starting supplements or changing medicines, and seek medical attention promptly for new or worsening symptoms such as numbness, balance problems, or confusion.
Sources
- NIH Office of Dietary Supplements, "Vitamin B12 — Health Professional Fact Sheet" — https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
- NHS, "Vitamin B12 or folate deficiency anaemia" — https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/
- NHS Inform, "Vitamin B12 or folate deficiency anaemia" — https://www.nhsinform.scot/illnesses-and-conditions/nutritional/vitamin-b12-or-folate-deficiency-anaemia/
By Putri PD
