Research explained
Vitamin B12 deficiency: who is at risk and why
Vitamin B12 deficiency means your body has too little B12, a vitamin your blood and nerves need. The main reasons are eating little or no animal food and taking metformin or acid-reducing medicines for years. A blood test is the only way to know.
The short answer
53%
People with low B12 in Indian studies from 2015 to 2020, pooled in a 2021 review
2×
How much more common low or borderline B12 was after 5 years of metformin than with a dummy pill
+65%
Higher odds of low B12 after 2 or more years of PPI acid reducers. This is a link, not proof.
2.2µg
B12 an Indian adult needs each day. It comes mainly from animal foods.
Strength of evidenceGood
Many studies agree that low B12 is common in vegetarians, and a long trial links metformin to low B12. The link with acid reducers comes from observational studies and is weaker.
Key findingB12 deficiency is common, especially in India. Eating little or no animal food, taking metformin for years and long-term acid reducers all raise the risk. If you have symptoms, ask a doctor for a blood test. Never stop a medicine on your own.
What B12 does, and what a deficiency causes
Vitamin B12 helps your body make DNA and healthy red blood cells. It also keeps the coating around your nerves healthy. B12 comes mainly from animal foods such as milk, curd, eggs, fish and meat. Some foods also have B12 added.
You need only a tiny amount. India’s nutrition experts advise about 2.2 micrograms a day for adults. A microgram is a millionth of a gram. But if you eat few animal foods, or your body can’t absorb B12 well, you can still run short.
Without enough B12, you can get anaemia. This means your blood has too few healthy red blood cells. Low B12 can also damage your nerves. Some of these problems can be serious, and some may not go away. That is why it helps to catch it early.
The UK’s 2024 guideline on B12, from an expert body called NICE, lists the most common symptoms:
- Tiredness you can’t explain (fatigue).
- Pins and needles, or numbness.
- Problems with balance or walking, and falls.
- Trouble focusing or remembering things, sometimes called brain fog.
- A sore, swollen tongue.
- Eyesight problems, such as blurred vision.
- Low mood or anxiety.
Many other conditions cause these symptoms too. You can also have low B12 without anaemia. So the only way to know is a blood test. If you have any of these symptoms, see a doctor.
Why vegetarians and vegans are at risk
A 2014 review looked at 40 studies of vegetarians and vegans. Low B12 was common in every age group. It was most common in vegans, especially those who didn’t take B12. The authors advise all vegetarians to get their B12 checked. They also say vegetarians should strongly consider a B12 supplement.
This matters for the many people in India who eat a vegetarian diet. India’s 2024 dietary guidelines call B12 “a challenge” for vegetarians. They note that milk has only a small amount of it.
In India’s national nutrition survey, almost 1 in 3 teens aged 10 to 19 had low B12. A 2021 review pooled Indian studies from 2015 to 2020. It found low B12 in about half the people tested. Those studies varied a lot, so treat that number as rough.
Metformin: the clearest medicine link
Metformin is a common medicine for type 2 diabetes. Doctors also use it for prediabetes, when blood sugar is high but not yet in the diabetes range. The best evidence on metformin and B12 comes from a long US trial.
This was a trial where people were put into groups by chance, so the groups could be fairly compared. After 5 years, low or borderline-low B12 was twice as common with metformin. Each extra year of metformin went with 13% higher odds of low B12.
Anaemia was also more common in the metformin group. Nerve problems in the feet were more common in people on metformin with low B12. But that finding rests on only 13 people. The authors say doctors should consider checking B12 in people who take metformin. The NICE guideline also lists metformin as a risk.
Metformin is an important medicine. Don’t stop or change it because of this. Ask your doctor whether a B12 test makes sense for you.
Acid reducers: a weaker link
Stomach acid helps your body take in B12 from food. Some common medicines lower stomach acid. They include PPIs, such as omeprazole and pantoprazole, and H2 blockers, such as famotidine. People take them for heartburn and acid reflux.
A large US study compared about 26,000 people with low B12 to about 184,000 people without it. Odds are a way of measuring how likely something is. Taking a PPI for 2 years or more went with 65% higher odds of low B12. Higher doses went with a stronger link. H2 blockers went with a smaller rise.
This kind of study compares people who have a condition with people who don’t. It shows a link. It can’t prove that one thing causes the other. People who need these medicines may differ in other ways.
A 2023 review pooled 25 studies. PPI users were a little more likely to have low B12, but the results differed a lot between studies. Most studies found no difference in B12 levels. The authors said the link was too weak to be clear.
Odds of low B12 with acid-reducing medicines
- PPIs for 2+ years1.65 (1.58–1.73)
- PPIs, over 1.5 pills a day1.95 (1.77–2.15)
- PPIs, under 0.75 pills a day1.63 (1.48–1.78)
- H2 blockers for 2+ years1.25 (1.17–1.34)
- PPIs, 25 studies pooled1.42 (1.16–1.73)
NICE still lists both kinds of acid reducer as risks. If you take one for a long time and have symptoms, ask your doctor about a B12 test. Don’t stop the medicine on your own.
Other causes doctors look for
Diet and these two medicines are not the only reasons for low B12. NICE lists several others:
- Autoimmune gastritis, where the body’s defences attack the stomach lining. Some people call it pernicious anaemia.
- Coeliac disease, a gut condition set off by gluten, and some other autoimmune conditions.
- Stomach or bowel surgery, including many weight-loss operations.
- A few other medicines, including colchicine, pregabalin and topiramate.
- Using nitrous oxide, or laughing gas, as a recreational drug.
Even in vegetarians, diet may not be the only cause. So a doctor may look further.
The vitamin B12 deficiency blood test
Doctors usually start with a total B12 or an active B12 test. In pregnancy, NICE advises the active B12 test. NICE reads the results like this:
| Result | Total B12 | Active B12 |
|---|---|---|
| Deficiency confirmed | below 180 ng/L | below 25 pmol/L |
| Unclear: another test may help | 180–350 ng/L | 25–70 pmol/L |
| Deficiency unlikely | above 350 ng/L | above 70 pmol/L |
Results in the middle band are unclear. If you also have symptoms, a second test called MMA (methylmalonic acid) can help. Labs may set their own limits, so check the range on your report. One nanogram per litre (ng/L) is the same as one picogram per millilitre (pg/mL).
Two things can confuse the test. A B12 supplement can raise your result without fully fixing a deficiency. The combined contraceptive pill can lower total B12 without causing a deficiency. So tell your doctor what you take, and get tested before you start a supplement if you can.
Claims and evidence
ClaimOnly vegans get low B12.
EvidenceIn 40 studies, low B12 was common in all kinds of vegetarians, though most common in vegans. Long-term metformin, some stomach problems and surgery can cause it in meat-eaters too.
ClaimIf you’re not anaemic, your B12 must be fine.
EvidenceNICE says not to rule out low B12 just because there is no anaemia. In the metformin trial, low B12 showed up even without anaemia.
ClaimAcid-reflux tablets always cause low B12.
EvidenceLong-term PPIs went with 65% higher odds in one large study. But a 2023 review of 25 studies found the link weak and inconsistent.
ClaimMilk gives vegetarians all the B12 they need.
EvidenceIndia’s dietary guidelines say milk has only a small amount of B12, and call B12 a challenge for vegetarians.
What this means for you
What this means for you
- If you eat little or no animal food, include milk, curd or eggs if you eat them, and foods with added B12. Ask your doctor about a B12 test and whether you need a supplement.
- If you take metformin or an acid reducer for a long time, ask your doctor whether a B12 test makes sense. Don’t stop or change the medicine on your own.
- See a doctor if you have tingling, numbness, balance problems, memory problems or tiredness you can’t explain.
- Get tested before you start a B12 supplement if you can. If you take one, NICE suggests a form called cyanocobalamin, methylcobalamin or adenosylcobalamin. Supplement quality varies.
- If you are pregnant, breastfeeding, have a health condition or take medicines, talk to a doctor or pharmacist before you start any supplement.
What the research can’t tell you yet
- Exact numbers for India. Indian studies used different tests and cut-offs, and their results varied a lot.
- Cause and effect for acid reducers. These studies only show links. People who need these medicines may differ in other ways.
- Who was studied. The metformin trial was in US adults with prediabetes, and B12 was measured only twice.
- Better tests. Many studies measured blood B12 alone. Other tests, such as MMA, give a fuller picture.
- Your own risk. This page can’t diagnose you. Only a test and a doctor can.
How Bodyvault uses this research
Add metformin or a PPI such as pantoprazole to Supplements, and Bodyvault Pro suggests asking your doctor whether a B12 test makes sense. Your B12 lab results also get a note about these medicines. If a result is low, Coach suggests talking to your doctor and, on a vegetarian profile, says food alone often isn’t enough. Bodyvault never tells you to stop a medicine, and it doesn’t yet recognise H2 blockers such as famotidine.
Share or cite this explainer
Bodyvault (2026). Vitamin B12 deficiency: who is at risk and why. https://bodyvault.app/blog/vitamin-b12-deficiency
The charts on this page may be reused with a link back to it. The underlying data belong to the studies cited below.
Questions
What causes B12 deficiency?
The main causes are a diet with little or no animal food, problems absorbing B12 and some long-term medicines. Absorption problems include autoimmune gastritis, coeliac disease and stomach or bowel surgery. The medicines include metformin and acid reducers.
What does a vitamin B12 deficiency cause?
It can cause anaemia, which means too few healthy red blood cells. It can also damage your nerves, which can cause pins and needles, numbness or balance problems. Some nerve damage may not go away, so see a doctor early.
What are the symptoms of B12 deficiency?
Common symptoms include tiredness you can’t explain, pins and needles, numbness, balance problems, memory trouble, a sore tongue, blurred vision and low mood. Many other conditions cause these too, so you need a blood test to know.
Can low B12 make you tired?
Yes. Tiredness you can’t explain, or fatigue, is one of the common symptoms NICE lists. But tiredness has many causes, so ask a doctor for a test rather than guessing.
What blood test checks for B12 deficiency?
Doctors usually test total B12 or active B12. NICE treats total B12 below 180 ng/L as a deficiency, and 180 to 350 ng/L as unclear. If the result is unclear, a second test called MMA can help.
Sources
- Pawlak R, Lester SE, Babatunde T (2014). The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: a review of literature. Eur J Clin Nutr 68(5):541–548.
- Aroda VR et al. (2016). Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab 101(4):1754–1761.
- Lam JR et al. (2013). Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA 310(22):2435–2442.
- Choudhury A et al. (2023). Vitamin B12 deficiency and use of proton pump inhibitors: a systematic review and meta-analysis. Expert Rev Gastroenterol Hepatol 17(5):479–487.
- NICE (2024). Vitamin B12 deficiency in over 16s: diagnosis and management. NICE guideline NG239.
- Venkatesh U et al. (2021). Micronutrient’s deficiency in India: a systematic review and meta-analysis. J Nutr Sci 10:e110.
- ICMR-National Institute of Nutrition (2024). Dietary Guidelines for Indians. ICMR-NIN, Hyderabad.
- ICMR-NIN Expert Group (2020). Nutrient requirements for Indians: recommended dietary allowances and estimated average requirements (brief note). ICMR-NIN, Hyderabad.
General information about fitness and nutrition, not medical advice. If you have a health condition, are pregnant or take medication, talk to your doctor before changing your diet or training.