Vitamin B12 (cobalamin) is needed to form the myelin that insulates the nerves, for the maturation of red blood cells and for DNA synthesis in every dividing cell. The body stores several years' supply in the liver, which means deficiency develops slowly, often over two to five years, and the symptoms creep in so gradually that they are attributed to age, stress or low mood. B12 is found only in animal foods (meat, fish, eggs, milk) and in fortified products, and absorption requires stomach acid that frees the vitamin from food and intrinsic factor from the stomach's cells that carries it through the gut wall. So you become deficient either from too little in the diet (vegans and vegetarians without supplements) or from poor absorption (acid blockers, metformin, atrophic gastritis in the elderly, pernicious anaemia, coeliac disease, Crohn's, gastric surgery, alcohol). The most important thing to know is that B12 deficiency can damage the nerves permanently if left untreated for long, that nerve symptoms can come before anaemia, and that the treatment is simple and cheap once the deficiency is found. This guide covers the symptoms, who is affected, the tests, the treatment, the time it takes, and the link to numbness in the feet, restless legs and iron deficiency.
Symptoms of B12 deficiency, in the order they usually come
| Area | Symptoms |
|---|---|
| General | Tiredness and lack of energy, breathlessness, palpitations, pallor with a slightly yellowish tone, dizziness, headache, reduced appetite and weight loss |
| Nerves (can come before the anaemia) | Tingling, numbness and a burning feeling in feet and hands (starts in the toes, symmetrically), reduced sensation and vibration sense, unsteady walking especially in the dark, weakness in the legs, restless legs, muscle twitches, poorer fine motor skills, in late cases difficulty walking |
| Brain and mood | Brain fog, worse memory and concentration, low mood, irritability, anxiety, in rare cases confusion or psychosis; in the elderly it can resemble dementia |
| Mouth and gut | Sore, red, smooth and burning tongue, mouth ulcers, cracks at the corners of the mouth, altered taste, constipation or diarrhoea |
| Other | Visual disturbance, tinnitus, darker skin in folds, infertility and miscarriage, pigment changes, premature grey hair |
In the elderly the symptoms are often just tiredness, unsteadiness and worse memory. In young vegetarians often tiredness, numbness and low mood. The nerve symptoms are what is urgent: the longer they have gone on, the greater the risk that they don't fully reverse.
Who gets B12 deficiency
- Vegans and vegetarians without supplements or fortified products; the stores last two to five years, then the deficiency comes. Everyone who eats fully plant-based needs a supplement, and anyone breastfeeding or pregnant needs it for the baby's sake.
- People over 60: one in ten is deficient, because the stomach lining thins (atrophic gastritis) and produces less acid and intrinsic factor.
- Acid blockers (omeprazole, pantoprazole, esomeprazole) for more than one to two years: without acid, B12 is not freed from food.
- Metformin (diabetes medicine) lowers absorption, and one in ten to five who take it for several years becomes deficient; a test should be taken yearly.
- Pernicious anaemia: an autoimmune disease where the body destroys the cells that make intrinsic factor; more common with other autoimmune disease (thyroid, type 1 diabetes, vitiligo) and in families. Requires lifelong treatment.
- Gastric and bowel surgery (gastric bypass, gastric sleeve, removed lower small intestine), coeliac disease, Crohn's disease, bacterial overgrowth in the small intestine, tapeworm.
- High alcohol consumption, nitrous oxide (also as a party drug, which destroys B12 acutely and can cause nerve damage within weeks), certain epilepsy medicines, the pill over a long time, HIV medicines.
- Pregnant and breastfeeding women with low dietary or store status; the baby is affected.
Tests and investigation
Ask for B12 (cobalamin) in the blood: under 150 pmol/l is deficiency, 150–250 is a grey zone where up to half have a functional deficiency, over 250 is usually normal. In the grey zone homocysteine and/or methylmalonic acid (MMA) decide, which rise when the cells lack B12; they are more sensitive than the B12 value itself. At the same time take haemoglobin, MCV (the red blood cells become large, over 100, with deficiency; but simultaneous iron deficiency makes them small and can hide it), folate (folate deficiency gives the same blood picture and should not be treated alone with B12 deficiency, because then the anaemia is hidden while the nerve damage continues), ferritin (iron deficiency and B12 deficiency often come together with a vegetarian diet and gut problems) and TSH. With an unclear cause: antibodies against intrinsic factor and parietal cells (pernicious anaemia), a coeliac test, gastroscopy. Don't take B12 supplements in the weeks before the test if you want to know your baseline, and say if you take biotin (interferes with some analyses).
Treatment: tablets or injections, and how long it takes
- High-dose tablets (1 mg cyanocobalamin daily, over the counter or on prescription) work for most people, even with poor absorption, since about one percent is absorbed passively without intrinsic factor; 1 mg then gives 10 micrograms, which is enough. Vegans can choose 50–100 micrograms daily or 1–2 mg once a week as prevention.
- Injections (hydroxocobalamin intramuscularly) are used with pronounced nerve symptoms, very low values, when tablets aren't absorbed or taken, and often as a start with pernicious anaemia: several injections the first weeks, then tablets or an injection every two to three months.
- Folic acid is given at the same time if folate is also low, but never alone with suspected B12 deficiency.
- Iron if ferritin is low; blood formation takes off when B12 is started and uses up iron and potassium quickly.
- Time: the blood picture starts correcting within a week and is normal after six to eight weeks; the tiredness eases after two to four weeks; the tongue and mouth heal in a few weeks; the nerve symptoms improve slowly over three to twelve months and can take up to a year and a half, and those that have existed for long don't always fully reverse; memory and mood improve over months. In the first period the symptoms can temporarily feel stronger as the nerves start to heal.
- How long: as long as the cause remains. Pernicious anaemia, gastric surgery and atrophic gastritis mean lifelong treatment; a vegetarian diet means supplements as long as you eat that way; with continued metformin and acid blockers, continue B12. Check the value after three months and then yearly.
There is no overdose risk with B12 (the excess is passed in urine), but don't take it instead of an investigation: the cause decides the treatment, and pernicious anaemia and stomach disease need follow-up.
The link to nerves, restless legs and iron deficiency
B12 deficiency damages the nerves in two ways: the myelin (insulation) breaks down and the long nerve tracts in the spinal cord that convey sensation and balance are affected. It starts as tingling and numbness symmetrically in the toes and soles, creeps upwards, and gives unsteadiness in the dark since the brain no longer gets information from the feet; see numbness and tingling in the feet for the other causes (diabetes, nerve entrapment, alcohol). Restless legs occur both with B12 deficiency and with iron deficiency, and the two deficiencies often come together with a vegetarian diet, coeliac disease, acid blockers and gastric surgery; anyone with restless legs should therefore test both ferritin and B12, see restless legs and iron deficiency. While the treatment works, daily movement (walks, cycling) that keeps the circulation to the nerves going helps, as does balance training (standing on one leg at the sink, walking a line, tandem stance, a minute a day) which trains the brain to compensate with vision and the inner ear, foot care (look at your feet daily if sensation is reduced, good shoes, no hot footbaths without checking the temperature with your hand), and light cupping and massage of feet, calves and thighs which increases blood flow in the skin and muscles, relieves crawling and heavy legs in the evening and gives the nerves better conditions to heal. Draw the dynamic cup with a little oil slowly from the toes towards the heel, from the ankle towards the knee and from the knee towards the hip, five minutes per leg, three to four evenings a week, with light pressure. Don't cup over skin you can't feel (you won't notice if it gets too hard), over sores, with new swelling, or on lower legs with varicose veins or poor circulation, and read when to avoid cupping. Cupping doesn't replace B12.
Read more
Iron deficiency, vitamin D deficiency, tiredness, numbness in the feet, restless legs, dizziness, and always cold.
Frequently asked questions
What are the symptoms of B12 deficiency?
Tiredness, breathlessness and pallor, tingling and numbness in feet and hands starting in the toes, unsteady walking especially in the dark, worse memory and concentration, brain fog, low mood, a sore red smooth tongue, mouth ulcers, dizziness and restless legs. The symptoms creep in over months to years, the nerve symptoms can come before the anaemia, and in the elderly it can resemble dementia.
Who gets B12 deficiency?
Vegans and vegetarians without supplements, one in ten over 60 (thinner stomach lining), those who have taken acid blockers for over one to two years, those who take metformin, people with pernicious anaemia (autoimmune), coeliac disease, Crohn's or gastric surgery, with high alcohol consumption and after nitrous oxide. Pregnant and breastfeeding women with low status pass the deficiency on to the baby.
Which tests should you have for suspected B12 deficiency?
B12 in the blood (under 150 pmol/l is deficiency, 150–250 a grey zone), and in the grey zone homocysteine or methylmalonic acid, which rise when the cells lack B12. At the same time haemoglobin and MCV, folate, ferritin (iron deficiency is often present too) and TSH. With an unclear cause: antibodies against intrinsic factor (pernicious anaemia), a coeliac test and gastroscopy. Don't take supplements in the weeks before the test.
How is B12 deficiency treated, and how long does it take?
High-dose tablets (1 mg a day) work for most people even with poor absorption; injections with nerve symptoms, very low values or pernicious anaemia, then maintenance. The blood picture corrects over six to eight weeks, the tiredness eases over two to four weeks, the nerve symptoms improve slowly over three to twelve months and don't always fully reverse if they have existed for long. Treatment continues as long as the cause remains, often for life.
Are B12 deficiency and iron deficiency linked?
Yes, they often come together with a vegetarian diet, coeliac disease, acid blockers, gastric surgery and heavy periods, they cause similar tiredness and restless legs, and the iron deficiency can hide the B12 deficiency's large red blood cells on the test. So test ferritin and B12 at the same time. When B12 is started, blood formation takes off and uses up iron, so iron often needs to be given in parallel.
Written by Curam. Last updated 17 October 2026. This is general self-care information and does not replace medical care. For sudden, severe or unusual symptoms, contact your doctor. Talk to your doctor before cupping if you are pregnant, take blood thinners or have a condition affecting skin, blood vessels or blood.
