Vitamin B12 Deficiency Symptoms: Who’s at Risk & What to Do

What Is Vitamin B12?

Vitamin B12 (cobalamin) is a water-soluble vitamin essential for red blood cell formation, nerve function, and DNA synthesis. Unlike most water-soluble vitamins, it’s stored in meaningful amounts in the liver — enough to last two to five years in a healthy adult — which is why deficiency tends to build slowly and often goes unnoticed until it’s fairly advanced.

Crucially, B12 is found almost exclusively in animal products. Plant foods don’t naturally contain it, which makes this one of the clearer nutritional gaps to plan around on a vegan or vegetarian diet.

Why Your Body Needs It

EFSA-authorised health claims for vitamin B12 include:

  • Contributes to the reduction of tiredness and fatigue
  • Contributes to normal energy-yielding metabolism
  • Contributes to normal functioning of the nervous system
  • Contributes to normal psychological function
  • Contributes to normal red blood cell formation
  • Contributes to normal homocysteine metabolism
  • Has a role in the process of cell division
  • Contributes to the normal function of the immune system

Signs of Vitamin B12 Deficiency

Because B12 is stored for years, symptoms often develop gradually over months and can be mistaken for other things:

  • Persistent fatigue and low energy
  • Pins and needles or numbness (typically hands and feet)
  • Pale or slightly yellow-tinged skin
  • Sore or inflamed tongue
  • Difficulty concentrating, brain fog, memory issues
  • Low mood or irritability
  • Poor balance or unsteady gait (more advanced cases)

Because many of these overlap with iron deficiency, both are usually checked together via a blood test rather than assumed from symptoms alone.

Who’s Most at Risk

  • Vegans and, to a lesser extent, vegetarians — the single biggest dietary risk factor, since B12 isn’t naturally present in plant foods
  • Adults over 50 and especially over 75 — stomach acid production declines with age, and acid is needed to release B12 from food
  • People with digestive conditions — Crohn’s disease, coeliac disease, or a history of gastric/bowel surgery can impair absorption
  • Long-term metformin users — the diabetes medication is known to reduce B12 absorption over time
  • People with pernicious anaemia — an autoimmune condition preventing B12 absorption, which requires medical management, not just supplementation

Food Sources

  • Meat, particularly liver
  • Fish and shellfish (clams and mackerel are especially rich)
  • Eggs
  • Dairy products
  • Fortified foods — some plant milks, nutritional yeast, and breakfast cereals in the UK/EU are fortified with B12, making them a genuinely useful source for vegans

Methylcobalamin vs Cyanocobalamin: Which Is Better?

For most people, both forms work. Cyanocobalamin is the most studied and most stable, and methylcobalamin is the form the body uses directly. There’s no strong evidence that methylcobalamin works better for healthy adults.

Cyanocobalamin is a synthetic form that the body converts into the active forms of B12. It’s very stable, inexpensive and used in most fortified foods and in much of the research on B12 supplementation. Its name puts some people off because it contains a cyanide group, but the amount is tiny and handled easily by the body.

Methylcobalamin is one of the two active forms of B12 found in the body. It doesn’t need converting, which is the basis of most marketing claims about it. In practice, the body converts cyanocobalamin efficiently, and studies comparing the two in healthy people haven’t shown a clear advantage for either.

Hydroxocobalamin is the form used in NHS B12 injections. It’s mentioned here because you may see it if your GP treats a deficiency.

When the choice might matter:

  • Smokers and people with kidney disease are sometimes advised to prefer methylcobalamin or hydroxocobalamin, as their bodies may handle the cyanide group less efficiently.
  • Everyone else can choose on price, dose and format. Consistency matters far more than the form.

Sublingual or swallowed? Sublingual tablets dissolve under the tongue. They’re convenient, but absorption is broadly similar to a swallowed tablet at the same dose. The exception is people who can’t absorb B12 through the gut (for example with pernicious anaemia), who usually need injections rather than any oral form.

  • Cyanocobalamin is the most common, stable, and affordable form
  • Methylcobalamin is the “active” form the body uses directly, often preferred by people wanting a form closer to what’s naturally metabolised
  • Sublingual (under-the-tongue) tablets are popular for faster absorption into the bloodstream, bypassing some digestive-tract absorption issues
  • Vegans and strict vegetarians should supplement or rely on fortified foods as standard practice, not just when symptoms appear

Our pick: Solgar Methylcobalamin B12 1000mcg — a sublingual, methylated form of B12.

Vegan Diet and Vitamin B12 Deficiency

If you follow a vegan diet, you need a reliable source of B12 from fortified foods or a supplement. This isn’t optional. B12 is made by bacteria, and in modern food supply it’s found almost only in animal products. Plant foods don’t provide it in a usable form.

Because the liver stores B12 for years, many people feel fine for a long time after going vegan and assume their diet is adequate. Deficiency can develop slowly and quietly, and some of its effects on the nervous system may be permanent if it goes on too long.

What the Vegan Society recommends (choose one):

  • Eat fortified foods two or three times a day to get at least 3 micrograms of B12 a day, or
  • Take one B12 supplement daily providing at least 10 micrograms, or
  • Take a weekly B12 supplement providing at least 2000 micrograms

Sources that aren’t reliable: spirulina, chlorella, seaweed, tempeh and unwashed vegetables are sometimes suggested as B12 sources. Many contain inactive B12 analogues that don’t meet your needs and can even make blood tests look better than your actual status.

Fortified foods that do help: many plant milks, breakfast cereals, yeast extract spreads and nutritional yeast in the UK and EU are fortified with B12. Check the label, as fortification varies between brands and products.

Vegetarians get some B12 from eggs and dairy but often less than they need, particularly if they eat these only occasionally. A supplement or regular fortified foods is a sensible precaution.

Pregnancy and breastfeeding: babies of vegan mothers with low B12 are at real risk of deficiency. If you’re vegan and pregnant or breastfeeding, discuss B12 with your midwife or GP.

Vitamin B12 and Fatigue: When It’s the Cause

Low B12 is a recognised cause of tiredness, but B12 supplements only help with fatigue if you’re actually low. “Vitamin B12 contributes to the reduction of tiredness and fatigue” is an EFSA-authorised claim. It describes what adequate B12 does, not an energy boost on top of normal levels.

B12 deficiency fatigue tends to come with other signs. Look out for:

  • Pins and needles or numbness in the hands and feet
  • Problems with balance or memory
  • A sore, red or smooth tongue
  • Pale or slightly yellow skin
  • Low mood or irritability

If your tiredness comes with any of these, ask your GP for a blood test that includes B12. If it doesn’t, other causes such as iron deficiency, poor sleep, thyroid problems or low vitamin D are more likely. → Why Am I Always Tired?

Normal blood test but still symptomatic? Serum B12 isn’t a perfect test. Some people have symptoms with results at the low end of normal. Your GP can request additional tests, such as methylmalonic acid or active B12, if symptoms suggest deficiency.

Don’t start supplements before a test if your GP is investigating your symptoms. Supplementing first can mask the result and make an underlying cause like pernicious anaemia harder to diagnose.

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Frequently Asked Questions

Can you take vitamin B12 and iron together?

Yes. They don’t interfere with each other’s absorption. → Iron guide · B12 vs Iron Deficiency

Can you take too much vitamin B12?

B12 has low toxicity, and EFSA hasn’t set an upper intake level because no adverse effects have been established at high oral doses. Your body absorbs only a small proportion of large doses and excretes much of the rest. That doesn’t mean unlimited doses are useful: if your levels are already adequate, more B12 won’t add benefit.

How long does it take for B12 supplements to work?

If you’re deficient, energy often starts improving within a few weeks. Nerve-related symptoms such as tingling can take months to improve, and some may not fully recover if the deficiency went on for a long time, which is why early diagnosis matters.

Does metformin affect vitamin B12?

Yes. Long-term use of metformin, a common type 2 diabetes medicine, can reduce B12 absorption. If you’ve taken it for several years, ask your GP whether your B12 should be checked.

What’s the best time of day to take B12?

It doesn’t matter much. Many people take it in the morning out of habit. B12 can be taken with or without food.

Should I take B12 with folic acid?

B12 and folate work together, and a GP may treat both if both are low. Taking high-dose folic acid alone can mask the blood signs of B12 deficiency while nerve damage continues, so don’t take high-dose folic acid without knowing your B12 status.

This page is for general educational purposes only and is not medical advice. Persistent numbness, balance issues, or memory changes should be checked by a GP — these can indicate a deficiency that needs medical, not just dietary, correction.

Sources & Further Reading

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