What causes B12 deficiency?

What causes B12 deficiency?

The most common cause in the UK is pernicious anaemia, an autoimmune condition in which the immune system attacks the stomach cells that make intrinsic factor, the protein you need to absorb B12 from food. NICE's 2024 guideline calls the underlying condition autoimmune gastritis. Most other cases come from diet, medicines, or problems with the stomach and gut.

• Pernicious anaemia. The NHS says it is more common in women around 60, in people with a family history of it, and in people with another autoimmune condition. NICE also lists thyroid disease, type 1 diabetes and coeliac disease among the risk factors for B12 deficiency.
• Diet. People who eat little or no meat, fish, milk, cheese or eggs are at risk, vegans in particular if they don't use fortified foods or a supplement. The body's stores last around 2 to 5 years, so problems can take years to appear after a change of diet.
• Medicines. NICE lists metformin, proton pump inhibitors (PPIs), H2-receptor antagonists, colchicine, phenobarbital, pregabalin, primidone and topiramate. The MHRA says low B12 is a common side effect of metformin and may affect up to 1 in 10 people who take it.
• Gut conditions and surgery. These include Crohn's disease, coeliac disease, removal of all or part of the stomach (gastrectomy), removal of the last section of the small intestine, many weight-loss operations, and past radiotherapy to the abdomen or pelvis.
• Recreational nitrous oxide.

The cause decides the treatment. If you take metformin or a PPI, don't stop it on your own: the MHRA advises people on metformin not to stop without talking to their doctor, and says B12 can be corrected while you carry on taking it.

What are the symptoms of low vitamin B12?

Tiredness and breathlessness are the most familiar, but the list is long and symptoms usually come on slowly. The NHS includes:

• extreme tiredness, lack of energy, feeling weak
• shortness of breath, palpitations and headaches
• pins and needles or numbness
• a sore, red tongue, sometimes with mouth ulcers
• problems with your vision
• problems with memory, understanding and judgement
• low mood, anxiety or confusion
• indigestion, loss of appetite or diarrhoea
• problems with balance and coordination, and muscle weakness

You can be deficient without being anaemic: NICE tells doctors not to rule out B12 deficiency just because a full blood count looks normal. Many of these symptoms have other causes too, so it takes a blood test to confirm.

What are the unusual symptoms of B12 deficiency?

These are the symptoms people tend to put down to something else. From the NHS and NICE lists:

• eyesight problems linked to the optic nerve, such as blurred vision or patches missing from your field of view
• mental health symptoms, which NICE says can include depression, anxiety or psychosis
• "brain fog": difficulty concentrating and short-term memory loss
• balance problems and falls, because the nerves that sense where your body is are affected
• incontinence
• during pregnancy, anaemia that isn't getting better with iron tablets

What does a B12 deficiency tongue look like?

Red, sore and often smooth. The NHS describes a sore or red tongue, sometimes with mouth ulcers; doctors call the inflammation glossitis. In atrophic glossitis the small bumps on the top of the tongue flatten, so the surface looks smooth and glossy. A 2022 study in China found B12 deficiency in 68% of 236 people with atrophic glossitis, against 3% of 208 healthy controls, and the authors suggested the tongue can be the first sign. Iron deficiency can also make your tongue sore, and only a blood test will tell you which it is.

Can B12 deficiency affect your nails?

Sometimes, but nail changes aren't on the NHS list of B12 symptoms. A 2015 dermatology review lists hair and nail changes among the skin signs of B12 deficiency, with darker skin pigmentation the most common. Case reports describe darkening of the skin and nails. In one report from India, a woman in her 80s with a very low B12 level had brownish nails and a dark band in one nail, and the band had reversed by 12 weeks of treatment. That is a single case, not a trial. Brittle or ridged nails have many causes, and the NHS lists spoon-shaped nails among the symptoms of iron deficiency anaemia. Our guides to the signs of low iron and biotin for hair and nails cover the other causes. A GP can arrange a blood test, so there's no need to guess.

Are low B12 symptoms different in women?

The symptoms are the same, but some details apply mainly to women:

• Pernicious anaemia is more common in women around 60.
• The combined contraceptive pill can lower total B12 on a blood test without causing a real deficiency, NICE notes, though a low result can still be genuine.
• In pregnancy, NICE recommends the active B12 test and treats anaemia that doesn't respond to iron as a possible sign. The NHS says B12 deficiency in pregnancy raises the risk of a neural tube defect in the baby, and that it can cause temporary infertility.
• Iron deficiency, very often caused by heavy periods or pregnancy, shares tiredness, breathlessness and a sore tongue with B12 deficiency. Our guide to the signs of low iron covers it.

Can B12 deficiency cause weight gain or hair loss?

Can B12 deficiency cause weight gain?

There's no good evidence that it does. Weight gain isn't on the NHS or NICE symptom lists, and the NHS lists loss of appetite. Some studies have found lower B12 levels in people with a higher BMI, but a 2018 systematic review of 19 of them could not establish the link, and observational studies like these can't show cause and effect anyway. If you are gaining weight and feel tired, an underactive thyroid is one thing a GP may check: the NHS lists weight gain, tiredness and hair loss among its symptoms, and NICE lists thyroid disease as a risk factor for B12 deficiency.

Can B12 deficiency cause hair loss?

It isn't on the NHS list of B12 symptoms. A 2019 review of vitamins and minerals in hair loss concluded there wasn't enough evidence to recommend testing for, or supplementing, B12 in the common types of hair loss. Iron deficiency is the nutritional cause the NHS names. Our guide to biotin for hair and nails covers what else to rule out.

What does a B12 blood test show?

It measures the B12 in your blood, using either total B12 (serum cobalamin) or active B12 (holotranscobalamin), usually alongside a full blood count and a folate level. NICE sets these thresholds:

Labs can use their own validated cut-offs. If you have symptoms and a result in the middle band, a second test, methylmalonic acid (MMA), can help. Some things skew the result:

• B12 supplements, including multivitamins, can push the number up without fully treating a deficiency. Tell the GP what you take and how much.
• The combined pill can lower total B12.
• People of Black ethnicity may have a higher normal range.
• The NHS notes that some people have symptoms despite normal levels.

Once deficiency is confirmed, the GP looks for the cause, which may mean a blood test for intrinsic factor antibodies. A negative result doesn't rule out pernicious anaemia.

Can you test your B12 at home?

Home B12 test kits are sold online, but the NHS route is a blood test arranged by your GP, and we couldn't find evidence that finger-prick kits match it. The NHS says a GP usually diagnoses B12 deficiency from your symptoms and blood tests, and that some people have symptoms despite normal results, so one number doesn't settle it. NICE advises taking blood for diagnostic tests before B12 replacement starts. If you use a kit, take the result to your GP along with your symptoms, and mention any B12 you take, because supplements can raise the result without fully treating a deficiency. Don't start high-dose B12 or stop a prescribed treatment on the strength of a kit result.

Is B12 deficiency treated with tablets or injections?

It depends on the cause, and some causes need injections. If diet is the cause, the NHS says you may be advised to take B12 tablets every day between meals, and people who stay vegan may need them for life. If the cause is pernicious anaemia, total removal of the stomach or removal of the end of the small intestine, NICE recommends lifelong injections. The NHS describes injections of hydroxocobalamin every other day at first, then every 2 to 3 months for life. Other absorption problems may be treated with injections or high-dose tablets of at least 1 mg a day. If you've had nerve symptoms, the NHS says you'll be referred to a haematologist and may need injections every 2 months.

Don't treat suspected anaemia with folic acid on your own. Folic acid can improve the blood picture enough to hide an underlying B12 deficiency while damage to the nervous system continues, which is why the NHS checks B12 before anyone starts folic acid.

How long does it take to recover from B12 deficiency?

Usually weeks to months. NICE says symptoms could start to improve within 2 weeks of starting treatment, may take up to 3 months, and can take much longer to go completely; they can even get worse at first. The NHS often repeats the blood test 7 to 10 days in and again at about 8 weeks, and NICE suggests a follow-up appointment at 3 months (1 month in pregnancy or while breastfeeding). The NHS warns that some problems can be permanent if treatment came late.

How long does B12 take to work?

For a diagnosed deficiency, the timeline above applies. If your levels were normal and you were hoping for more energy, bear in mind NICE's point that these symptoms overlap with many other conditions. Tiredness that doesn't lift needs a GP to find the cause.

Which foods contain vitamin B12?

Vitamin B12 is found naturally in meat, fish, eggs, milk and cheese, and it is added to some breakfast cereals and plant-based foods. The NHS notes that it isn't found naturally in fruit, vegetables or grains. Adults need about 1.5 µg a day, so a 200 ml glass of semi-skimmed milk (1.8 µg) covers that on its own. These are approximate amounts per portion from NHS dietetic services and the British Dietetic Association (BDA):

Liver is by far the richest source, but the NHS advises avoiding it in pregnancy. Amounts in fortified products vary by brand, so check the label.

Which vegan foods contain vitamin B12?

Fortified foods and supplements are the dependable vegan sources. The NHS suggests breakfast cereals fortified with B12, unsweetened soya drinks fortified with B12, and yeast extract or nutritional yeast flakes with added B12. One of the BDA's worked examples reaches 2.3 µg a day with a bowl of fortified cereal and plant drink, a fortified plant yoghurt and yeast extract on toast. Not every plant drink is fortified, so check the label. NHS dietitians say seaweed, algae, spirulina and fermented foods such as miso are not good sources, because they contain an inactive form of the vitamin that the body can't use. If you rely on a supplement, the BDA recommends 10 µg a day or at least 2 mg a week, and says long-term vegans should have their B12 checked, because a high folate intake can mask a deficiency.

Should you take a B12 tablet or supplement?

Most people who eat meat, fish, eggs or dairy get enough B12 from food, and the NHS says vegans may need a supplement. B12 tablets are also used to treat some deficiencies. A patient leaflet from an NHS integrated care board describes about 50 to 150 µg a day for 3 months for a deficiency caused by diet, then at least 10 µg a day if food can't provide enough. Your GP or pharmacist sets the dose, and tablets don't suit every cause: NICE recommends injections for pernicious anaemia. A 2025 systematic review of 16 studies (6,098 people) found that swallowed and under-the-tongue B12 raised blood B12 about as much as injections, though the studies varied widely and the authors flagged possible publication bias. If you buy a B12 supplement, NICE advises choosing one that contains cyanocobalamin, methylcobalamin or adenosylcobalamin, because some products don't contain enough B12, or the right type. Tell your GP what you take before a blood test.

Cyanocobalamin or methylcobalamin: which form of B12 is better?

There's no good evidence that one form works better for most people. NICE's 2024 guideline names cyanocobalamin, methylcobalamin and adenosylcobalamin as the forms to look for in an over-the-counter product, and an NHS integrated care board patient leaflet lists all three as suitable. Cyanocobalamin, the form named on cyanocobalamin tablets, is a synthetic form. Methylcobalamin, also sold as methyl B12, is one of the two active forms the body uses. A 2015 review concluded that supplying the active forms is unlikely to be better than cyanocobalamin or hydroxocobalamin, because every form follows the same route inside cells. A 2017 narrative review argued that natural forms are preferred, but its abstract describes no head-to-head trials, and one author is affiliated with a supplement company. Choose by the amount of B12 on the label and the form your GP or pharmacist suggests, and follow your treatment plan if you have a diagnosed deficiency.

Do B12 sprays work?

We found no trial comparing a B12 spray with tablets, so we can't say whether sprays work better, worse or the same. The research we found covers B12 taken under the tongue (sublingual) or swallowed. A 2025 systematic review of 16 studies and 6,098 people found sublingual and oral B12 raised blood B12 and lowered homocysteine by about as much as injections, though results varied a lot and the authors flagged possible publication bias. A 2020 review described the evidence for nasal B12, a different route, as a few preliminary studies. For any vitamin B12 spray, check the label for the amount and form of B12, and don't use a spray instead of injections if you have pernicious anaemia. Tell your GP before a blood test, because supplements can push the result up.

Can you overdose on vitamin B12?

There is no well-documented overdose from tablets. The NHS says there isn't enough evidence to show what high daily doses of B12 supplements do, and that 2 mg or less a day from supplements is unlikely to cause any harm. The UK Expert Group on Vitamins and Minerals set the same 2 mg guidance figure in 2003. It found only a handful of case reports of problems from B12 taken by mouth: five allergic reactions, three of them in people who had earlier been given B12 by injection, and one rash resembling acne rosacea. That is why there's no established list of symptoms of too much B12.

A high B12 result when you aren't taking supplements is a different matter. A 2013 review in Clinical Chemistry and Laboratory Medicine linked unexpectedly high levels with liver and kidney disease and some cancers, so it is worth discussing with your GP.

Where Natura fits

Daily B12, in the Natura cabinet (coming soon), is 1000 µg of vitamin B12 as methylcobalamin, which is under the NHS figure of 2 mg a day. Vitamin B12 contributes to normal red blood cell formation and to the reduction of tiredness and fatigue. It is also in the Blood Pack with Daily Iron, which is not a treatment for anaemia: if you have symptoms, a diagnosed deficiency or pernicious anaemia, follow your GP's treatment, and if you're due a B12 blood test, tell them you take it. Both are listed with the daily bottles and body systems packs.