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 body's stores last around 2 to 5 years, 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, listed below. A blood test from your GP settles it, and the 2024 NICE guideline sets out what to do with a borderline result.⁸ Caught early, everything reverses; left for years, nerve damage can be permanent.

• 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

Sources checked on 29 October 2026.

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, which is megaloblastic anaemia, with pallor, palpitations and sometimes a faint yellow tint to the skin.^{1, 3} 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 sometimes blurred vision. 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 improves with treatment. For sleep: which vitamin deficiency affects sleep.^{1, 3}

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.^{1, 3} None is diagnostic on its own; together with tiredness or tingling they point to a test. 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.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 most common cause in the UK 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, 3}

Medicines. Metformin roughly doubles the odds of B12 deficiency (odds ratio 2.45 across 29 studies and 8,089 patients) and NICE lists it among the causes to test for; proton pump inhibitors and H2 blockers reduce the acid needed to free B12 from food; nitrous oxide, including recreational use, inactivates B12 and is listed as a cause by both the NHS and NICE.^{3, 5, 8}

Higher need. Pregnancy and breastfeeding, where a vegan mother's baby can become deficient in its first months.¹

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. Bone or muscle pain with the tiredness points to vitamin D: see signs of vitamin D deficiency and how to check your vitamin D levels. The 2024 NICE guideline sets an indeterminate band, total B12 of 180 to 350 nanograms per litre or active B12 of 25 to 70 pmol per litre; for someone with symptoms it recommends a further test of methylmalonic acid, and it says deficiency should not be ruled out because anaemia is absent.⁸ If you are being tested, do not start a B12 supplement until the blood has been taken, because it masks the result; if you are vegan or over 65 and no test is planned, routine B12 should not wait for one.⁸ 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 the NHS puts the ceiling for folic acid supplements at 1 mg a day.^{6, 9} Finger-prick kits measure total B12, which in the borderline band needs the follow-up test.⁸ B12 for women covers the overlap with iron deficiency.

Can B12 deficiency be a sign of cancer?

Very rarely. Pernicious anaemia, one of the ordinary causes above, carries an increased long-term risk of stomach cancer, 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, usually pernicious anaemia or a gut condition.^{3, 8} The deficiency itself does not cause cancer, and treating it does not increase risk.

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 dose, the minimum NICE sets where absorption is the problem, and a Cochrane review of 3 trials in 153 people found oral and injected B12 raised blood levels similarly, on low-certainty evidence.^{7, 8} If the cause is pernicious anaemia or absent absorption, hydroxocobalamin injections are given, every other day at first and then every two to three months for life; with nerve symptoms the NHS refers to a haematologist and injections may be every two months.³ NICE says symptoms can begin to improve within 2 weeks but may take up to 3 months, and longer to clear completely; the NHS rechecks the blood at about 8 weeks and warns that long-untreated nerve damage can be permanent.^{3, 8}

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 years or 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.⁹ Vegans need fortified foods or a supplement, the NHS says, and a daily 10 microgram tablet sits well inside its 2 mg a day guidance; deficiency affects 1 in 20 people aged 65 to 74 and 1 in 10 aged 75 or over, so a fortified food or supplement makes sense from the mid-sixties; NICE lists metformin among the causes to test for.^{3, 4, 8, 9, 11} A single B12 supplement covers 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 when a single B12 suits better.

What we don't know

• Where "low normal" ends and deficiency begins. The 2024 guideline's indeterminate band reflects genuine uncertainty.⁸
• How many people with normal serum B12 and symptoms have a functional deficiency. Probably some; the second-line tests are rarely 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. Wanting to eat ice or other non-food items (pica) is on the NHS list of iron deficiency symptoms, and the two deficiencies often coexist.¹⁰

How long does it take to reverse B12 deficiency?

NICE says symptoms can start to improve within 2 weeks and may take up to 3 months, with complete recovery taking longer; the NHS rechecks the blood at about 8 weeks. Long-standing nerve damage may not fully reverse.^{3, 8}

Why am I suddenly B12 deficient?

It is rarely sudden; stores run down over years. Common triggers are starting metformin or acid suppressants, a diet change, age, or pernicious anaemia developing. Nitrous oxide use can cause rapid deficiency.^{3, 8}

Sources

1. Green R, et al. Vitamin B12 deficiency. Nature Reviews Disease Primers, 2017. Narrative review; funding not stated on PubMed. 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. Retrospective record review, 170 adults; funding not stated on PubMed. PubMed 25563739.
3. NHS. Vitamin B12 or folate deficiency anaemia: overview, symptoms, causes, treatment and complications. Pages last reviewed 20 February 2023 (review overdue). nhs.uk.
4. Niklewicz A, et al. A systematic review and meta-analysis of functional vitamin B12 status among adult vegans. Nutrition Bulletin, 2024. Systematic review, 19 studies, 17 meta-analysed; funding not stated on PubMed. PubMed 39373282.
5. Niafar M, et al. The role of metformin on vitamin B12 deficiency: a meta-analysis review. Internal and Emergency Medicine, 2015. Pooled analysis, 29 studies, 8,089 patients; funding not stated on PubMed. PubMed 25502588.
6. Miller JW, et al. Excess folic acid and vitamin B12 deficiency: clinical implications? Food and Nutrition Bulletin, 2024. Narrative review; one author holds a B12 assay patent. PubMed 38987872.
7. Wang H, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database of Systematic Reviews, 2018. Systematic review, 3 randomised trials, 153 people, 3 to 4 months; authors declare no conflicts. PubMed 29543316.
8. NICE. Vitamin B12 deficiency in over 16s: diagnosis and management. NICE guideline NG239, published 6 March 2024. nice.org.uk.
9. NHS. Vitamins and minerals: B vitamins and folic acid. Page last reviewed 3 August 2020 (review overdue). nhs.uk.
10. NHS. Iron deficiency anaemia. Page last reviewed 26 January 2024. nhs.uk.
11. NHS. The vegan diet. Page last reviewed 5 June 2026. nhs.uk.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.

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; if a test is planned, do not start B12 supplements until it has been taken.