Signs of Vitamin B12 Deficiency: Symptoms, Causes and Recovery

The signs of vitamin B12 deficiency are tiredness and weakness, breathlessness on exertion, pale skin with sometimes a faint yellow tinge, a sore red smooth tongue and mouth ulcers, pins and needles or numbness in the hands and feet, unsteadiness, poor memory and concentration, and low mood or irritability.¹ They build slowly, because the liver stores several years' worth, and the nerve symptoms can appear while the blood count is still normal, which is why "my bloods were fine" does not rule it out.^{1, 2} The causes are few and specific: not eating animal foods, the stomach losing the ability to absorb B12 with age or through pernicious anaemia, metformin and acid-suppressing medicines, and gut conditions or surgery. A blood test from your GP settles it, and the 2024 UK guideline sets out what to do with a borderline result.³ Caught early, everything reverses; left for years, nerve damage can be permanent, which is the reason to act on the signs rather than wait.

• Blood signs: tiredness, breathlessness, palpitations, pallor, faint yellowing, headaches
• Mouth signs: sore, red, smooth tongue; mouth ulcers; altered taste
• Nerve signs: pins and needles, numbness, unsteadiness, clumsiness, blurred vision; may come first
• Mind and mood: poor memory and concentration, irritability, low mood, confusion in older adults
• Causes: vegan or vegetarian diet, age, pernicious anaemia, metformin, omeprazole and similar, coeliac or Crohn's disease, stomach or bowel surgery

What B12 deficiency feels like

It starts as tiredness that sleep does not fix and breathlessness on stairs, because B12 is needed to make red blood cells and without it the cells that are made are large, fragile and few; that is megaloblastic anaemia, and it brings pallor, a racing heart and sometimes a faint lemon-yellow tint to the skin as fragile cells break down.¹ The mouth joins in: the tongue becomes smooth, red and sore, taste changes, ulcers appear. Then the nerves: B12 maintains the fatty sheath around them, and its lack causes pins and needles and numbness that begin in the feet and hands, unsteadiness on the feet especially in the dark, clumsiness, and in some people blurred vision or a change in how things feel underfoot. The brain is affected too: poor concentration and memory, irritability, low mood, and in older adults a confusion that can be mistaken for dementia and that improves with treatment.^{1, 2} Not everyone gets every sign, and the nerve and mood symptoms can come before the anaemia.

The facial signs people search for

Pale skin, a faint yellow tinge to the skin and whites of the eyes, a smooth red swollen tongue, cracks at the corners of the mouth and mouth ulcers, and sometimes patches of darker skin or early greying of hair. None is diagnostic on its own; together with tiredness or tingling they point to a test. "What do you crave when your B12 is low?" has no evidence-based answer: B12 deficiency does not cause specific cravings, and the ice-chewing craving belongs to iron deficiency, which often travels with it. What vitamin B12 is good for explains the roles behind these signs.

What causes B12 deficiency?

Not enough in. B12 occurs naturally only in animal foods, so vegans and many vegetarians run short unless they take a supplement or eat fortified foods; plant foods that claim B12, such as seaweed and tempeh, contain mostly inactive forms.⁴ Foods high in B12 lists the sources.

Not absorbed. B12 from food needs stomach acid to free it and a protein called intrinsic factor to carry it. Both decline with age, so people over about 65 absorb food B12 poorly. Pernicious anaemia, an autoimmune condition that destroys the cells making intrinsic factor, is the classic cause and needs lifelong injections. Coeliac disease, Crohn's disease, and surgery on the stomach or the last part of the small bowel all reduce absorption.¹

Medicines. Metformin lowers B12 over years and UK guidance now asks for periodic testing; proton pump inhibitors and H2 blockers reduce the acid needed to free B12 from food; nitrous oxide, including recreational use, inactivates B12 and has caused severe nerve damage in young people.⁵

Higher need. Pregnancy and breastfeeding, where a vegan mother's baby can become deficient in its first months.

How do you test for it, and what does "low normal" mean?

Your GP will test serum B12, usually with folate and a full blood count, and ferritin if iron deficiency is also possible. The 2024 NICE guideline recognises an indeterminate band, where the result is not clearly low or normal, and recommends a second test, either active B12 or a marker called methylmalonic acid, before deciding; it also says that symptoms with a borderline result should not simply be dismissed.³ Two practical points. Do not start a B12 supplement before the test, because it masks the result. And if you take folic acid, say so, because folic acid can correct the anaemia of a B12 deficiency while the nerve damage continues, which is why doses above 1 mg are prescription-only.⁶ There is no reliable home test for B12 deficiency; finger-prick kits measure serum B12, which is the least informative measure in the borderline band. B12 for women covers how iron deficiency from heavy periods hides B12 deficiency.

Can B12 deficiency be a sign of cancer?

Very rarely, and the answer is a GP investigation rather than fear. Most B12 deficiency has one of the ordinary causes above. Pernicious anaemia, one of those causes, carries a modestly increased long-term risk of stomach cancer because of the inflammation in the stomach lining that goes with it, which is why people with pernicious anaemia are advised to report new stomach symptoms. An unexplained B12 deficiency in someone who eats animal foods and takes no relevant medicines is a reason for the GP to look for the cause, which will usually be pernicious anaemia or a gut condition and occasionally something else.¹ The deficiency itself does not cause cancer, and treating it does not increase risk; the point is that "unexplained" deserves an explanation.

How is it treated, and how long until you feel better?

If the cause is diet or medicines, high-dose oral B12 works for most people, because about 1% of a large dose is absorbed without intrinsic factor; 1,000 micrograms a day is the usual oral treatment, and a Cochrane review found it as effective as injections for raising levels in those who can absorb some.⁷ If the cause is pernicious anaemia or absent absorption, hydroxocobalamin injections are given, loading over two weeks and then every two to three months for life; where there are nerve symptoms, injections are given more often until they stop improving. Tiredness and mood often lift within a week or two of starting; the blood count normalises over two months; tingling and unsteadiness improve over three to six months and can take a year, and damage present for more than six months before treatment may not fully reverse.^{1, 2} That timeline is the argument for testing early. Self-injecting with ampoules bought abroad, which forums discuss, is not something this page can advise on; the NHS route exists for the people who need injections.

Who should ask for a test

Anyone with several of the signs above; anyone with pins and needles, numbness or unsteadiness without another explanation; vegans and vegetarians not taking B12; adults over 65 with tiredness or memory concerns; people on metformin for more than a few years or on long-term acid suppressants; people with coeliac disease, Crohn's disease, a thyroid or other autoimmune condition, or previous stomach or bowel surgery; women with heavy periods whose iron has been treated but tiredness persists; and anyone using nitrous oxide recreationally with any nerve symptom, urgently.

Preventing it

Meat, fish, eggs and dairy a few times a week cover the 1.5 microgram daily need for most people. Vegans should take 10 micrograms or more a day or 2,000 micrograms a week; over-65s should get some B12 from fortified foods or a supplement; people on metformin should be tested periodically.^{3, 4} Wellgard's vegan vitamin B12 is a single high-dose option for those groups; vitamin B12 contributes to normal red blood cell formation, normal functioning of the nervous system and the reduction of tiredness and fatigue. Which is better, B12 or B complex explains why a complex rarely has enough.

What we don't know

• Where "low normal" ends and deficiency begins. The 2024 guideline's indeterminate band reflects genuine uncertainty.³
• How many people with normal serum B12 and symptoms have a functional deficiency. Probably some; the second-line tests are not routinely done.

Frequently asked questions

What are the first signs of B12 deficiency?

Tiredness, breathlessness on exertion and a sore tongue are common early signs; pins and needles in the feet can come first in some people.¹

What are the facial signs of B12 deficiency?

Pallor, a faint yellow tinge, a smooth red tongue, cracked mouth corners and mouth ulcers. None is diagnostic alone.

What do you crave when your B12 is low?

Nothing specific; B12 deficiency does not cause cravings. Craving ice is a sign of iron deficiency, which often accompanies it.

How long does it take to reverse B12 deficiency?

Energy and mood improve within weeks, the blood count over two months, nerve symptoms over three to twelve months. Long-standing nerve damage may not fully reverse.^{1, 2}

Why am I suddenly B12 deficient?

It is rarely sudden; stores run down over years. Common triggers for the diagnosis are starting metformin or acid suppressants, a diet change, age, or pernicious anaemia developing. Nitrous oxide use can cause rapid deficiency.⁵

Which organ is affected by B12 deficiency?

The bone marrow, where blood cells are made, and the nervous system, including the spinal cord and brain. The stomach is often the cause rather than the victim.

Sources

1. Green R, et al. Vitamin B12 deficiency. Nature Reviews Disease Primers, 2017. PubMed 28660890.
2. Solomon LR. Functional cobalamin (vitamin B12) deficiency: role of advanced age and disorders associated with increased oxidative stress. European Journal of Clinical Nutrition, 2015. PubMed 25563739.
3. NHS. Vitamin B12 or folate deficiency anaemia. nhs.uk; NICE guideline NG239, Vitamin B12 deficiency in over 16s, 2024.
4. Niklewicz A, et al. A systematic review and meta-analysis of functional vitamin B12 status among adult vegans. Nutrition Bulletin, 2024. PubMed 39373282.
5. Niafar M, et al. The role of metformin on vitamin B12 deficiency: a meta-analysis review. Internal and Emergency Medicine, 2015. PubMed 25502588.
6. Miller JW, et al. Excess folic acid and vitamin B12 deficiency: clinical implications? Food and Nutrition Bulletin, 2024. PubMed 38987872.
7. Wang H, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database of Systematic Reviews, 2018. PubMed 29543316.

This article is general information, not medical advice. Pins and needles, numbness, unsteadiness, memory change or an unexplained anaemia need a GP and a blood test; do not start B12 supplements before being tested.