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B12 & Folate Deficiency

Two vitamins that produce almost the same blood picture and completely different consequences if you get them the wrong way around. B12 deficiency can damage nerves permanently, and folate taken without checking B12 first can correct the blood test while that damage continues. That single fact is why this page exists.

Kidney & Blood Evidence-Based

Last updated:

🚨 Never treat a suspected deficiency with folic acid alone without checking vitamin B12 first. Folate corrects the anemia of B12 deficiency, so the blood count returns to normal and the problem appears solved, while the neurological damage of untreated B12 deficiency continues and can become permanent71. This applies to high-dose folic acid supplements and to B-complex products containing large amounts of folate.
Definition

What Is B12 and Folate Deficiency?

Both vitamins are needed to make DNA, so both are needed to make red blood cells. Running short of either produces large, immature red cells and the same anemia, called megaloblastic anemia. On a complete blood count they can look identical.

They part company outside the bone marrow. B12 is also needed to maintain the myelin sheath around nerves, and prolonged deficiency causes a progressive neurological syndrome affecting sensation, balance and eventually cognition. Folate does not do this.

And crucially, the neurological damage of B12 deficiency can occur before, or entirely without, any anemia6, which is why a normal blood count does not exclude it and why symptoms of numbness and unsteadiness deserve a B12 test rather than reassurance.

💡 Key Insight: In countries like the US and UK, the most common cause of B12 deficiency is not a diet low in B12 6. It is failure to absorb it, from autoimmune loss of intrinsic factor, from age-related stomach changes, from bowel disease or surgery, or from long-term medicines. That matters because a deficiency of absorption is not fixed by eating more liver.
Small, even normal red blood cells beside larger immature ones, and a nerve fiber whose myelin sheath is smooth at one end and frayed at the other, with panels on why B12 must be checked before folate and on common causes

🧠 B12 protects nerves

Prolonged deficiency damages the spinal cord and peripheral nerves, producing numbness, pins and needles, unsteadiness and, later, cognitive change. Treated early, many of the symptoms improve. Left long enough, some of the damage is permanent61.

💊 Common medicines deplete it

Metformin is associated with lower B12 levels and with deficiency in long-term users2. Long-term acid suppression reduces absorption too, since stomach acid is needed to release B12 from food.

🌱 Plants do not supply B12

B12 comes from animal foods and fortified products. Spirulina, algae and most seaweeds contain inactive analogs that do not work in humans and can make a blood test look falsely reassuring3.

By the Numbers

B12 and Folate Deficiency by the Numbers

1 in 10
people aged 75 or over have a B12 or folate deficiency, and 1 in 20 of those aged 65 to 74 6
Over 1 mg
of folic acid a day can mask B12 deficiency, which can damage the nervous system if missed; that is why B12 is checked before folic acid is started9
400 mcg
of folic acid a day is advised for anyone pregnant, trying for a baby or who could get pregnant, until 12 weeks of pregnancy, to help prevent neural tube defects such as spina bifida9
2 to 5 years
how long the body's B12 stores can last, so a deficiency can take years to appear after a change of diet10
7 to 10 days
after treatment starts, when a first blood test usually checks that it is working, with another at about 8 weeks7
Similar
B12 levels with 1,000 mcg a day by mouth as with injections, in three small trials of 153 people (low-quality evidence); when autoimmune gastritis is the cause, injections are used for life11
Signs & Symptoms

Symptoms of B12 and Folate Deficiency

Symptoms come on slowly and vaguely and are often mistaken for aging, stress or depression.

SymptomWhat happens
Fatigue and breathlessness on exertionThe anemia itself. Worth knowing: Shared with iron deficiency, and the two can coexist.
Numbness or pins and needlesUsually feet first, then hands, often symmetrical. Worth knowing: A B12 sign, not a folate one. Report it promptly rather than waiting.
Unsteadiness, worse in the darkBalance depending on vision because position sense is impaired. Worth knowing: Suggests spinal cord involvement. This is the presentation that must not be delayed.
Sore, smooth, red tongueGlossitis, sometimes with mouth ulcers. Worth knowing: Occurs with both deficiencies.
Memory difficulty, low mood, irritabilityOften attributed to aging or depression. Worth knowing: B12 deficiency is one of the things worth excluding before concluding it is depression.
Pale or slightly yellow skinA lemon tinge, from anemia plus mild jaundice. Worth knowing: Reflects red cells being destroyed in the marrow.
Symptoms with a normal blood countNeurological symptoms and no anemia at all. Worth knowing: Possible, and the reason a normal complete blood count does not exclude B12 deficiency6.
⚠️ Who is most likely to be deficient. People over about 50, in whom stomach acid production commonly falls. Vegans and strict vegetarians, and breastfed infants of vegan mothers. Anyone on long-term metformin2 or long-term acid suppression; see GERD. People with celiac disease, Crohn's disease or previous bowel or stomach surgery. Anyone pregnant or trying for a baby, who needs more folate: folic acid before conception and in early pregnancy helps prevent neural tube defects9, so follow your prenatal care provider's advice. Heavy drinkers, in whom folate deficiency is common. And people with autoimmune conditions, since pernicious anemia travels with them; see thyroid disorders.
Causes

Causes of B12 and Folate Deficiency

B12 deficiency usually comes from failed absorption, and folate deficiency from low intake or higher need, which is why the cause decides the treatment7.

CauseHow It Contributes to B12 and Folate DeficiencyWhat Helps
Autoimmune gastritis (pernicious anemia)The immune system attacks the stomach cells that make intrinsic factor, which B12 needs in order to be absorbed. It is one of the most common causes of B12 deficiency, and more common in women around 60, with a family history or with another autoimmune condition10B12 replacement for life, usually by injection12. No food or tablet on this page replaces it
Stomach or bowel surgery, and gut conditionsRemoving part of the stomach, and conditions such as Crohn's disease, can stop enough B12 from being absorbed; celiac disease can do the same for folate10Treating the gut condition, with B12 replacement matched to the cause: for life by injection after a total gastrectomy or complete terminal ileal resection12
Diets without animal foodsB12 comes from meat, fatty fish, eggs and dairy, so people on a vegan diet who take no supplement or fortified foods are at risk10A reliable supplement, as the supplement section sets out; tablets are usually enough when diet is the cause7
MedicinesAcid-reducing medicines, a common diabetes medicine and nitrous oxide can lower B12; some anticonvulsants and some other medicines lower folate or make it harder to absorb10A prescriber review: B12 replacement while the medicine continues, and a check on whether it is still needed12. Never stop a prescribed medicine yourself
Poor diet and heavy drinking (folate)The body cannot store folate for long, its supply usually lasting about 4 months, so a diet short of vegetables and legumes, or regular heavy drinking, leads to folate deficiency10Folate-rich foods from the diet section, less alcohol and folic acid tablets for about 4 months once B12 has been checked7
Higher need: pregnancy and some illnessesPregnancy, some blood disorders, cancer and inflammatory illness raise the body's need for folate10400 mcg of folic acid a day before conception and until 12 weeks of pregnancy, with a higher dose only on medical advice9
Diagnosis

How B12 and Folate Deficiency Are Diagnosed

The important part is establishing why, because the cause determines whether tablets will work at all.

TestWhat it shows
Complete blood count and blood smearAnemia and large red cells. Worth knowing: Can be entirely normal in B12 deficiency with neurological damage. Also normal-looking if iron deficiency coexists, since the two cell changes cancel out.
Serum B12The first-line test. Worth knowing: An imperfect test with a gray zone. A borderline result in someone with symptoms deserves further testing rather than dismissal.
Serum or red cell folateFolate status. Worth knowing: Serum folate moves with recent meals; red cell folate reflects longer-term status.
Methylmalonic acid (MMA) and homocysteineFunctional markers that rise before stores are exhausted, useful in the gray zone. Worth knowing: Not available everywhere, and MMA also rises in kidney impairment.
Intrinsic factor antibodiesPernicious anemia, the autoimmune cause. Worth knowing: Insensitive, so a negative result does not exclude it.
Celiac serologyA treatable malabsorptive cause. Worth knowing: Must be done while still eating gluten; see celiac disease.
Medication reviewMetformin and long-term acid suppression, both common and both reversible contributors. Worth knowing: Requires someone to ask; a prescriber conversation, never a reason to stop a medicine yourself.
Thyroid functionAutoimmune thyroid disease travels with pernicious anemia. Worth knowing: See thyroid disorders.
💡 Ask for B12 and folate to be checked together, and ask what the cause is. If the cause is dietary, tablets work. If the cause is failure to absorb, as in pernicious anemia or after stomach surgery, standard-dose tablets may not be enough and injections are usually used. Being told your level is low without being told why leaves you unable to know whether the treatment offered will actually fix it.
Treatment Comparison

Conventional and Holistic Treatment for B12 and Folate Deficiency

🌿 HOLISTIC
💊 CONVENTIONAL
🌿

Holistic / Functional Approach

Food sources, reliable supplementation where diet cannot supply it, and fixing what is depleting you

Where Diet Works
Dietary deficiency, which responds fully to food or oral supplementation
Where It Does Not
Absorption failure. Pernicious anemia and post-surgical deficiency are not corrected by eating differently
Timeline
Blood counts usually recover within 2 to 4 weeks. Nerve symptoms often improve over 3 to 12 months, and the earlier treatment starts, the more can recover8
Limitation, stated plainly
Nothing dietary treats pernicious anemia, which needs lifelong medical replacement

Full Holistic Approach Includes

  • B12 from animal foods or a reliable supplement, since plants do not supply the active form3.
  • Folate from leafy greens and legumes, which is easy to reach from food.
  • A reliable B12 supplement if you are vegan, which is not optional and is not covered by algae products.
  • Reviewing metformin and acid suppression with your prescriber, not stopping them yourself.
  • Reducing alcohol, which impairs folate absorption and use.
  • Treating the underlying gut condition where there is one.
  • Retesting, to confirm the correction actually happened rather than assuming.
🌿 Worth knowing: this is one of the few pages on this site where a nutrient genuinely is the treatment. The catch is that it only works when the cause is intake rather than absorption.
Supplement Protocol

Evidence-Based Supplements for B12 and Folate Deficiency

The order in which you take these matters more than the dose.

🚨 Test B12 before starting folic acid, and test before starting B12 too. Starting B12 first makes a subsequent test uninterpretable, so if you suspect deficiency, get the blood test before the supplement rather than after. And never take high-dose folate to treat unexplained anemia or fatigue without a B12 result in hand, for the reason at the top of this page71. B-complex and multivitamin products frequently contain both, but do not rely on that to protect you.
SupplementWhat it is forTypical rangeTimingNotes & cautions
Vitamin B12 Correcting a confirmed deficiency, and routine prevention for vegans and many older adults. Set with your clinician. Higher oral doses are used where absorption is impaired, and injections where it fails Daily, or as prescribed Water-soluble and well tolerated. The form matters less than whether you can absorb it at all, which is a question about cause. Confirm the correction by retesting rather than assuming.
Folic acid Correcting confirmed folate deficiency, and preconception and early pregnancy supplementation on your prenatal care provider's advice. As directed by your clinician or prenatal care team Daily Only after B12 has been checked, outside of the pregnancy indication where it is standard advice. Also note that folate interacts with methotrexate; on that medicine, follow your rheumatology team (see rheumatoid arthritis). Some anticonvulsants also lower folate.
Iron, only if also deficient Correcting coexisting iron deficiency, which is common and can hide the large-cell picture on a blood count. Test ferritin and complete blood count first; dose set with your clinician As advised, away from tea, coffee and calcium Do not supplement iron without testing. See iron-deficiency anemia.
🚨 What to avoid, specifically. Algae, spirulina, chlorella and seaweed as a B12 source, which supply inactive analogs and can make a test look falsely adequate3. High-dose folic acid taken for tiredness without a B12 result. Assuming a B-complex covers it without checking the label. Stopping metformin or acid suppression yourself because you read they deplete B12; that is a prescriber conversation. And treating persistent numbness or unsteadiness as something to monitor rather than something to have assessed, because the window in which nerve damage can recover is limited.
💡 Where the real leverage is. Getting both tested together, finding out why rather than only that the level is low, treating B12 before folate and retesting to confirm it worked. If you are vegan or over 50, a reliable B12 source taken routinely prevents dietary deficiency, though not deficiency caused by failed absorption.
What to Expect

What to Expect Over Time

What happens depends on the cause, and on whether nerves are involved.

Treatment and supportive care, together
First Weeks

Blood is taken before B12 is started, but with nerve symptoms treatment does not wait for the results12. B12 is usually given by injection at first, and folic acid only after B12 has been checked; a blood test about 7 to 10 days in checks the response7.

Months 1 to 3

A second blood test at about 8 weeks confirms the treatment is working7, and a follow-up about 3 months after starting asks whether symptoms have improved12. Folic acid is usually taken for about 4 months7.

Months 3 to 12

Treatment settles by cause: tablets if diet was the cause, and regular injections if it was not7. Many symptoms improve with treatment, but some nerve problems can be permanent6.

Long Term

Autoimmune gastritis and some bowel surgery need B12 for life, even once symptoms have gone12. A vegan diet needs a reliable B12 source for life7.

When to Seek Care

See a clinician promptly, without waiting for a routine appointment, for new numbness or pins and needles, balance problems or falls, difficulty walking, memory or concentration changes, or blurred vision, because nerve damage from B12 deficiency can become permanent6. Go back if symptoms get worse or return on treatment12.

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Next Steps

Check B12 Before Folate

Get both levels tested together, find out why they are low, and treat B12 before or alongside folate. A dietary shortfall responds to food or oral replacement, but absorption failure needs medical treatment. Report new numbness or unsteadiness promptly.

Explore Iron-Deficiency Anemia → Explore Celiac Disease →

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed October 20, 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.4 This page is nutrition education, not medical advice, and it does not replace your doctor. A low B12 or folate needs a cause, not just a supplement. Pernicious anemia and other absorption failures require medical replacement for life and are not corrected by diet. Neurological symptoms need assessment promptly rather than a trial of tablets. What nutrition education can do is help you understand the evidence well enough to have a better conversation with the clinician who does treat you.

  1. Green R, et al. Vitamin B12 deficiency. Nat Rev Dis Primers. 2017;3:17040. PubMed 28660890. The source for the neurological consequences of untreated deficiency, for the fact that neurological damage can occur without anemia, and for the caution that folate can correct the hematological picture while neurological damage progresses. Also the basis for treating B12 before or alongside folate rather than after it. ↩ ↩ ↩ ↩
  2. Metformin use and vitamin B12 deficiency in people with type 2 diabetes. touchREVIEWS in Endocrinology. 2024;20(2). PubMed 39526048. Long-term metformin use is associated with lower B12 levels and with deficiency, with risk rising with dose and duration. This is a reason to monitor, and a prescriber conversation, not a reason to stop a medicine that is treating diabetes. See diabetes. ↩ ↩
  3. On algae and seaweed as B12 sources: spirulina, chlorella and most seaweeds contain corrinoid compounds that are structurally similar to B12 but biologically inactive in humans, and which can interfere with some assays so that a measured level appears adequate. See the NIH Office of Dietary Supplements vitamin B12 fact sheet, ods.od.nih.gov, and the Linus Pauling Institute entry on vitamin B12, lpi.oregonstate.edu. ↩ ↩ ↩ ↩
  4. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic. ↩
  5. On lifelong injections: NICE guideline NG239 recommends offering lifelong intramuscular vitamin B12 replacement when autoimmune gastritis, the cause of pernicious anemia, is the cause or suspected cause of deficiency, and after a total gastrectomy or complete terminal ileal resection, NICE NG239, 2024. ↩
  6. On how common deficiency is and what treatment can undo: NHS guidance states that B12 and folate deficiency affect around 1 in 10 people aged 75 or over and 1 in 20 aged 65 to 74, that pernicious anemia is the most common cause of B12 deficiency in the UK while a diet lacking the vitamins is uncommon, that nerve and other problems can occur without anemia, and that although many symptoms improve with treatment, some problems, such as those of the nervous system, can be permanent, which is why diagnosis and treatment should not be delayed, NHS, vitamin B12 or folate deficiency anemia. ↩
  7. On treatment and monitoring: NHS guidance states that treatment depends on the cause. B12 is usually given by injection at first; when diet is the cause, daily tablets between meals may follow, and when it is not, injections every 2 to 3 months for life. Folic acid is usually taken for about 4 months, and B12 is checked before it is started because folic acid can mask a B12 deficiency, which, if missed, can affect the nervous system. A blood test about 7 to 10 days after starting, and another at about 8 weeks, check that treatment is working, NHS, treating B12 or folate deficiency. ↩
  8. On the pace of recovery: a 2025 review of B12-⁠related spinal cord damage reports that blood counts typically return to normal within 2 to 4 weeks of treatment, that nerve problems often improve but may take 3 to 12 months, and that potassium should be monitored early in treatment because cells take up more potassium as they recover, PubMed 41008332. ↩
  9. On folic acid doses: NHS guidance recommends 400 mcg of folic acid daily for anyone pregnant, trying for a baby or who could get pregnant, until 12 weeks of pregnancy, to help prevent neural tube defects, with a higher dose of 5 mg for some women on a doctor's advice, and warns that folic acid doses above 1 mg can mask B12 deficiency, which can go on to damage the nervous system, a particular concern in older people, NHS, B vitamins and folic acid. ↩
  10. On causes: NHS guidance lists autoimmune loss of intrinsic factor (pernicious anemia, more common in women around 60, with a family history or another autoimmune condition), a vegan diet without supplements or fortified foods, stomach surgery, Crohn's disease and some medicines (acid-reducing drugs, a common diabetes medicine and nitrous oxide) as causes of B12 deficiency, noting that B12 stores can last 2 to 5 years. For folate, the store lasts about 4 months. Deficiency follows a poor diet, heavy drinking, malabsorption such as celiac disease, some medicines (including anticonvulsants) or higher need in pregnancy, blood disorders, cancer and inflammatory illness, NHS, causes of B12 or folate deficiency. ↩
  11. On tablets versus injections: a Cochrane review of three small randomized trials (153 people, 3 to 4 months) found that 1,000 mcg of oral B12 a day gave B12 levels similar to injections, on low-quality evidence; no trial measured symptoms. This does not apply where absorption has failed permanently, where injections are used for life, PubMed 29543316. ↩
  12. On diagnosis and follow-up: the 2024 NICE guideline on B12 deficiency advises taking blood for testing before starting B12, but not delaying treatment while results are awaited in people with suspected megaloblastic anemia and neurological symptoms. It recommends lifelong intramuscular B12 when autoimmune gastritis is the cause or suspected cause, or after a total gastrectomy or complete terminal ileal resection; replacement while a medicine that lowers B12 continues, with a review of whether that medicine is still needed; a first follow-up about 3 months after starting; and a return visit if symptoms worsen, come back or are new. It lists balance problems and falls, pins and needles or numbness, impaired walking, memory and concentration problems and blurred vision among the common signs, NICE NG239. ↩