Vitamin B12 or folate deficiency anaemia
The bone marrow needs vitamin B12 and folate (also called vitamin B9, or folic acid in its supplement form) to build normal red blood cells.
On this page
- How it makes itself known
- Lack of B12 hits the nerves, not only the blood
- Where a shortage of vitamin B12 comes from
- Why folate runs short
- How it is worked out which one is missing
- Why treatment must not start with folic acid alone
- Treatment: what, how and for how long
- Folic acid before and at the start of pregnancy
- Online consultation
Medicines commonly prescribed for Vitamin B12 or folate deficiency anaemia
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: CAPSULE, 1000 µgActive substance: cyanocobalaminManufacturer: Farmasierra Laboratorios S.L.Prescription requiredDosage form: TABLET, 5 mgActive substance: folic acidManufacturer: Aristo Pharma GmbhPrescription requiredDosage form: TABLET, 1000 microgramsActive substance: cyanocobalaminManufacturer: Italfarmaco S.A.Prescription required
The bone marrow needs vitamin B12 and folate (also called vitamin B9, or folic acid in its supplement form) to build normal red blood cells. When one of the two runs short, cell division stumbles: fewer red cells are made than usual, and the ones that emerge are large, immature and poorly equipped to carry oxygen. This anaemia is called megaloblastic, and a blood count separates it easily from iron deficiency, where the red cells are small and pale instead. The distinction is not a technicality: the treatment is entirely different, and the iron that many people start taking on their own initiative does nothing here. But the most important part of this subject is not the blood at all. Vitamin B12 is also needed for the sheaths around the nerves, and damage to the nerves is the most serious part of the illness and the part most often missed.
How it makes itself known
Everything builds up slowly, over months, and people usually have time to get used to their state and to put it down to work, age or too little sleep. The usual set of complaints: constant tiredness that sleep does not fix, weakness, breathlessness and a racing heart on exertion that used to be easy, headaches, pallor, ringing in the ears, dizziness on standing up.
There are more recognisable signs too. The tongue becomes smooth and bright red, as though varnished, and reacts painfully to hot or spicy food; mouth ulcers appear, along with cracks at the corners of the lips. Appetite goes, taste changes, there is nausea, bloating, unreliable bowels, and weight is lost. The skin sometimes takes on a faint yellowish tinge, which happens when faulty red cells break down early.
Do not wait for a routine appointment if chest pain, breathlessness at rest or on the slightest movement, fainting or a very fast heartbeat appear: in severe anaemia the heart is working at its limit, and that needs attention the same day — with chest pain, an ambulance.
Lack of B12 hits the nerves, not only the blood
This is the single thing worth taking away from the whole text. Vitamin B12 goes into building myelin, the sheath along which nerves carry their signal. When it runs short, the peripheral nerves and the back of the spinal cord suffer, and a picture appears that is entirely separate from the anaemia:
- numbness, tingling, a sensation of pins and needles or burning in the feet and hands, usually on both sides and symmetrically, starting with the toes;
- unsteadiness on walking, particularly in the dark and with the eyes closed, a feeling of walking on cotton wool, loss of confidence on stairs;
- weakness in the legs, cramps, tripping and falls;
- worse memory and concentration, difficulty finding words, slowed thinking, confusion;
- low mood, anxiety, irritability, and in older people a state easily mistaken for the beginning of dementia;
- trouble passing water, reduced sex drive and, less often, blurred vision.
Then come the two circumstances that make this part of the illness go missing so often. The first: the nerves can suffer before the blood does. Haemoglobin may be perfectly normal and the red cells of ordinary size, and the person is sent home with "your blood test is fine". This is not rare, and a full blood count on its own is not enough to rule out B12 deficiency. The second: the longer it goes on, the less of it can be undone. Blood recovers in weeks; nerves take months, and not always completely. Where neurological problems have been present for about a year or more, some of them usually stay for good. That is why numb feet and unsteadiness are not a reason to "keep an eye on it" but a reason to have blood taken now.
Where a shortage of vitamin B12 comes from
The body keeps a store of vitamin B12 in the liver that lasts several years, so a deficiency creeps in long before the first complaints. Almost always the trouble is not that there is too little vitamin on the plate, but that it is not being absorbed.
- Pernicious anaemia. The commonest cause of B12 shortage in adults. The immune system attacks the cells in the stomach that make intrinsic factor, the protein without which the vitamin simply is not absorbed in the gut. It is more common in older people, alongside other autoimmune conditions — thyroid disease, type 1 diabetes, vitiligo — and where there is a family history.
- Stomach and bowel surgery. Removal of part of the stomach, weight-loss surgery, resection of the last part of the small bowel, which is exactly where B12 is absorbed.
- Bowel disease. Coeliac disease, Crohn's disease, atrophic gastritis, conditions with bacterial overgrowth in the small bowel.
- Medicines. Metformin taken long term, and drugs that reduce stomach acid — proton pump inhibitors and H2 blockers. B12 is worth checking from time to time in people on them.
- Diet. Vitamin B12 occurs only in animal foods, so strict vegetarianism and especially veganism without supplements or fortified foods lead sooner or later to deficiency. The same applies to a breastfed baby if it is the mother following a vegan diet.
- Nitrous oxide. "Laughing gas", used for pain relief and, unfortunately, recreationally as well, inactivates vitamin B12 in the body. Repeated inhaling produces severe nerve damage, sometimes in very young people.
Why folate runs short
Here the mechanism is different. The body's store of folate lasts only a few months; it dissolves in water and is not laid down for later, so it has to arrive continuously, and a deficiency develops quickly — in weeks and months rather than years.
- A monotonous diet. Folate is found in green leaves, broccoli and other brassicas, pulses, asparagus, beetroot, citrus fruit and nuts. A diet in which almost none of this appears is the commonest cause. Long cooking destroys a good part of the vitamin.
- Alcohol. Regular drinking interferes with absorbing and holding on to folate, and usually comes with a poor diet. It is one of the most widespread causes in adults.
- Poor absorption. Coeliac disease and other conditions of the small bowel that damage its lining.
- Medicines. Some anti-epileptic medicines, methotrexate, sulfasalazine, and long-term use of drugs that interfere with folate metabolism.
- Higher demand. Pregnancy and breastfeeding, prematurity, rapid growth, haemolytic blood disorders, psoriasis and other states with fast cell turnover, long-term dialysis.
How it is worked out which one is missing
The starting point is a full blood count, which shows the haemoglobin and the average size of the red cells. Large red cells are a strong clue, but there is a trap here too: if iron is short at the same time, the sizes average out and look normal. Next come blood levels of vitamin B12 and folate.
Borderline B12 results are common and settle very little on their own, so where symptoms persist a doctor may add finer measurements — homocysteine and methylmalonic acid, both of which rise when the deficiency is real at tissue level even though the vitamin in the blood looks acceptable. If pernicious anaemia is suspected, antibodies against intrinsic factor and against the stomach cells are looked for. Thyroid function, coeliac antibodies and liver and kidney function are usually checked at the same time, and if the picture is unclear the person is referred to a gastroenterologist or a haematologist and a gastroscopy is discussed.
Things worth telling the doctor in advance: any stomach or bowel surgery, every medicine including over-the-counter remedies for heartburn, what the diet looks like, alcohol and any use of nitrous oxide, and autoimmune conditions in the family. And separately, every neurological sensation, even if it seems trivial: those are what change both the urgency and the treatment plan.
Why treatment must not start with folic acid alone
This is the most dangerous point in the whole subject, and the mistake is made with the best of intentions. Folic acid is sold over the counter and costs almost nothing, and the blood picture looks the same in both deficiencies. Someone with numb feet and a low haemoglobin starts taking folic acid — and the blood test really does improve: the red cells return to normal size, the haemoglobin rises, and for a while they feel better.
But folic acid does nothing for the nerves. If the real cause was B12 deficiency, blood production is put right while the destruction of the nerve sheaths carries on — only now silently, because the blood test, the one alarm signal there was, has gone back to normal. Months are lost that way, and with them the reversibility of the nerve damage. That is why the order is strict: vitamin B12 is measured first and, if it is low, replacing B12 comes first, with folic acid added afterwards. There is only one everyday exception to this rule — folic acid taken by a healthy woman planning a pregnancy, which is covered below.
Treatment: what, how and for how long
Once the cause is clear, treatment is usually straightforward and works well. The logic is worth grasping: what is replaced is not "vitamins in general" but precisely what is missing, and the route depends on why the shortage arose.
In pernicious anaemia, and after stomach or bowel surgery, tablets in ordinary doses are useless: the absorption mechanism itself is broken, and the vitamin will not get from the gut into the blood. The treatment is injections of vitamin B12 (hydroxocobalamin is the usual form): frequent at first, as a course that fills the store quickly, and then maintenance injections at fixed intervals. And it is treatment for life. The cause does not go anywhere, and stopping the injections after a year or two means the anaemia and the nerve problems come back. Where the nerves are affected, injections are given more often and for longer at the start, and recovery is measured in months.
If the deficiency comes from the diet, B12 tablets and a change of eating are usually enough; with veganism a supplement or fortified foods are needed permanently, not as a course. Folate deficiency is treated with folic acid tablets, normally for a few months and for longer if the underlying cause persists. Doses are always set by a doctor.
What happens next. General wellbeing and the tongue usually improve within the first weeks; the blood picture within one or two months, with a repeat test confirming that the treatment is working. Neurological symptoms are the slowest to retreat and do not always go completely. One thing to know separately: pernicious anaemia carries a raised risk of stomach cancer, so persistent abdominal pain, difficulty swallowing, vomiting, black stools or unexplained weight loss are reasons to be seen without delay.
Folic acid before and at the start of pregnancy
This is the case where a simple tablet genuinely prevents a tragedy. The neural tube, from which the brain and spinal cord develop, forms in the first weeks of pregnancy, often before a woman knows she is pregnant. An adequate folate level at that moment markedly reduces the risk of neural tube defects, the best known of which is spina bifida.
Hence the practical conclusion: the supplement is started before conception, not once the pregnancy is confirmed, and continued through the first twelve weeks. The usual preventive dose is four hundred micrograms a day. It is higher in particular situations — diabetes, treatment with anti-epileptic medicines, substantial excess weight, blood disorders, coeliac disease, and a neural tube defect in the family or in a previous pregnancy; in those cases the dose is set by a doctor.
A shortage of folate during pregnancy also raises the risk of premature birth and of low birth weight. Vitamin B12 deficiency in the mother is not a matter of indifference to the baby either, so with a vegan diet, after stomach surgery, or where there are complaints of numbness, both levels should be measured rather than only one.
Online consultation
A remote conversation fits this subject particularly well, because almost everything here is settled by going through symptoms and test results. The doctor will ask how long the tiredness, breathlessness and palpitations have been there, whether there is numbness, tingling, unsteadiness or any change in memory and mood, what the tongue looks like, what is happening with eating, weight and bowels; and will ask about surgery, bowel disease, autoimmune conditions in the family, alcohol and every medicine being taken, metformin and heartburn remedies included. It helps to have a recent blood count and the full list of medicines ready.
By the end it is usually clear which tests are needed first and in what order, what must not be started on one's own initiative, and what to raise at the face-to-face appointment. What comes afterwards is also convenient to handle online: how to read the results, why the injections will be lifelong, how to manage supplements on a vegan diet, what to take when planning a pregnancy. The limits are clear: blood cannot be taken remotely, and an examination is needed to assess nerve damage. And if chest pain, breathlessness at rest or fainting appear, there is no consultation to wait for — that is an ambulance.
This material is for information only and does not replace medical advice.
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Discuss your symptoms and possible next steps for Vitamin B12 or folate deficiency anaemia with a doctor online.
