Vitamin B12 Deficiency:
Symptoms, Causes & Who Really Needs to Top Up

1. What is vitamin B12 deficiency?

Your body needs vitamin B12 (cobalamin) at three decisive points: for blood formation in the bone marrow, for the protective sheath around the nerve fibres (myelin) and for cell division. When it runs short, several systems suffer at once — which is why the picture is so varied and often recognised only late.^¹

One peculiarity makes the deficiency treacherous: the liver stores B12 for several years. A deficiency therefore develops insidiously — your diet may have stopped supplying enough, or absorption may have been disturbed, long before the first complaints appear.

The route from food into the blood is surprisingly complicated, and every stage can fail: stomach acid releases B12 from the protein it is bound to in food, the stomach lining supplies intrinsic factor — a transport protein without which B12 is not absorbed — and only in the final section of the small bowel does the complex pass into the blood. It is exactly this chain that explains why stomach conditions, bowel conditions and certain long-term medicines are among the most important causes — more on that below.^¹,²

2. Symptoms: blood, nerves, mind

Blood formation: the signs of anaemia

Without B12 the body produces too few red blood cells, and strikingly enlarged ones (megaloblastic anaemia). Typical consequences are persistent tiredness, paleness, a drop in performance and breathlessness on exertion. A smooth, reddened, burning tongue also occurs — more on that under burning tongue.

Nervous system: the critical signs

Nerve involvement often begins with tingling and numbness in the hands and feet, frequently symmetrical and in a stocking or glove pattern. Later, unsteadiness when walking, disturbed position sense and muscle weakness can be added. In the most severe cases damage to the spinal cord develops (subacute combined degeneration).^²,⁴

Brain and mind

B12 deficiency can also show itself “upstairs”: with problems concentrating, forgetfulness, irritability or low mood. In older people in particular this is easily misread as “normal ageing” — when in fact B12 status is part of the standard work-up for declining mental performance.^¹,⁴

3. Causes: why B12 runs short

A B12 deficiency rarely arises because someone “eats too little” — on a mixed diet, food usually covers the requirement well. Far more often the problem lies with absorption:^¹,²

• Chronic inflammation of the stomach lining — gastritis, especially the autoimmune form, reduces both stomach acid and intrinsic factor.
• Pernicious anaemia — the classic autoimmune cause: immune cells turn against the parietal cells of the stomach or directly against intrinsic factor; those affected usually need lifelong supplementation.^⁴
• Medicines — metformin and proton pump inhibitors such as pantoprazole or omeprazole can lower B12 levels when taken long term — so often overlooked that they get a section of their own below.
• Bowel conditions and operations — Crohn's disease affecting the final section of the small bowel, coeliac disease and operations on the stomach or bowel interfere with absorption directly.
• A purely plant-based diet — in a usable form, B12 occurs practically only in foods of animal origin; without a supplement the stores run empty over the years on a vegan diet.^³
• An increased requirement — pregnancy and breastfeeding raise the requirement; a deficiency in the mother affects the child as well.
• Nitrous oxide — repeated use of nitrous oxide (as a party drug, for instance) can also render B12 unusable and trigger severe nerve damage.

4. Risk groups: who is particularly affected

• Older people: stomach acid production and absorption both decline with age — often on top of several long-term medicines. More on this in the guide medications in old age.
• People with type 2 diabetes taking metformin: years of use plus older age make checks particularly worthwhile — see type 2 diabetes.
• Long-term users of acid blockers: anyone taking proton pump inhibitors for years belongs on the monitoring list too.
• People living vegan or vegetarian: on a vegan diet a reliable B12 supplement is indispensable according to the professional societies; on a vegetarian diet the intake can also become tight.^³
• People with conditions or operations affecting the stomach and bowel: chronic gastritis, Crohn's disease, coeliac disease, weight-loss surgery on the stomach.
• Pregnant and breastfeeding women: particularly on a largely plant-based diet, B12 status should be kept in mind medically.

5. Diagnosis: why a normal B12 level can mislead

Honesty pays off here: the standard laboratory value — total B12 in the serum — is a coarse sieve. It also measures B12 that is bound to transport proteins and not available to the cells at all. In the lower part of the “normal range” in particular, a functional deficiency can already be present despite an unremarkable value.^²

• Holotranscobalamin (holo-TC): measures only the active B12 that is available to cells, and shows an emerging deficiency earlier and more reliably than the total value. It is recommended as the next step when findings are borderline.^²
• Methylmalonic acid (MMA) and homocysteine: metabolic products that build up when the cells really are short — they confirm the diagnosis in unclear cases.
• Full blood count: enlarged red blood cells (a raised MCV) are a classic clue — but their absence does not rule a deficiency out, particularly if iron is short at the same time.
• Looking for the cause: where a deficiency is confirmed and neither diet nor medicines explain it, the cause needs investigating — for example antibodies against intrinsic factor and parietal cells if pernicious anaemia is suspected.

6. Treatment: tablets or injections?

The good news: a B12 deficiency can almost always be put right. The choice between tablets and injections depends on the cause, the severity and on whether nerve symptoms are present — the decision is made by the treating practice together with you.

7. Metformin, pantoprazole & co.: medicines as a cause

This is the section missing from many B12 articles — and the brite angle on it: two of the most frequently prescribed long-term medicines in Germany can measurably lower B12 levels. If you take them for years, you should know about the connection.

Metformin: the overlooked classic

Metformin is the key first-line medicine in type 2 diabetes — nothing in this section changes that. But it is known that long-term use can interfere with B12 absorption in the final section of the small bowel; reduced B12 levels are described in the SmPC as a possible consequence of long-term use.^⁵ That becomes particularly relevant because a B12 deficiency causes nerve damage that is easily confused with a polyneuropathy caused by the diabetes itself — in which case the wrong cause may be treated for years. With long-standing metformin use, regular B12 checks are therefore considered sensible, especially where there is anaemia or tingling in the feet.^⁵

Proton pump inhibitors: less acid, less B12

Acid blockers such as pantoprazole and omeprazole throttle stomach acid — and that acid is exactly what is needed to release B12 from the protein it is bound to in food. Lower B12 levels are described with use over years; the evidence is less clear-cut here than for metformin, but the risk rises with duration and dose.^¹,² A low B12 value is therefore also a good reason to have the ongoing indication for the acid blocker reviewed medically — many long-term prescriptions simply run on without a current reason.

8. Telling it apart: iron deficiency and other look-alikes

Tiredness, paleness, problems concentrating — the same complaints are produced by iron deficiency anaemia, which is by far the more common form of anaemia. The difference lies in the blood count: with iron deficiency the red blood cells are typically too small, with B12 deficiency too large. It gets tricky when the two come together — for instance with chronic gastritis or coeliac disease, which disturb the absorption of iron and B12 at the same time: the changes in the blood count can then mask each other, and only targeted laboratory testing brings clarity. You will find the practical basics in the guide iron deficiency.

Two further look-alikes belong on the list. A folate deficiency changes the blood count in just the same way as a B12 deficiency — but if only folate is topped up while B12 is missing, the blood count can improve while the nerve damage carries on. That is why both values belong together. And persistent tiredness with problems concentrating can equally fit an underactive thyroid — that too is part of the standard work-up for this pattern of complaints.^⁴

9. Everyday life and prevention

• Make supplementation routine — whether it is a daily tablet or an injection appointment every few months: with B12 deficiency, treatment fails on regularity rather than on the substance.
• Vegan? Plan the supplement in — on a purely plant-based diet a reliable B12 preparation is a must, not an optional extra, according to the professional societies. Fortified foods on their own do not count as a secure source.^³
• Think of the laboratory with metformin and acid blockers — raise the check actively at your next routine appointment, especially if tiredness or tingling are new.
• Do not take high doses blind — B12 preparations from the chemist look harmless, but they can obscure the diagnosis. Measure first, then top up in a targeted way; what to watch out for with over-the-counter preparations is set out under supplements and medications.
• Keep your medication list up to date — a complete list of all your long-term medicines makes it easy for the practice to spot nutrient traps. How to do it is shown in keeping a medication list.

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