Vitamin B12
A vitamin from animal foods, taken mostly to top up a low level.
- Topping up low levels
- Memory and thinking
- Nerve pain and sensation
- Blood sugar
- Pregnancy and early life
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
Compare vitamin B12 prices per dose
On this page
What is vitamin B12?
Vitamin B12, also called cobalamin, is a water-soluble vitamin the body cannot make for itself. Only certain bacteria and archaea can build the molecule, which is why it reaches us mainly through animal foods, and why every supplement is grown by microbial fermentation rather than pressed from a plant. Inside cells it works as a helper for two enzymes, one in the body of the cell and one in the mitochondria, and through them it has a hand in DNA, in red blood cells and in the nervous system. Reviews call low B12 a worldwide public health problem, and long-term metformin, taken by more than a hundred million people, is linked with lower levels; between them, much of why it sells as it does.
Why do people take vitamin B12?
Topping up low levels
The thinking. People take vitamin B12 above all to bring a low reading back up. It comes mainly from animal foods, and long-term metformin, the first-choice tablet for type 2 diabetes, is linked with more low readings, especially at higher doses. For years an injection at the surgery was the usual route, so researchers asked whether a tablet does the same job.
What research has found. Two reviews compared how the vitamin gets in. The larger pooled thirteen studies and over four thousand adults: tablets by mouth, an injection into the muscle and a tablet held under the tongue all raised blood levels, with no significant difference between them. The smaller, covering three randomised trials, found 1,000 micrograms a day by mouth matched the injections, and cost less. This is one of the best-studied uses, and several reviews of trials broadly agree.
Memory and thinking
The thinking. B12 is one of the vitamins the nervous system leans on: reviews describe its part in the cell’s energy processes, in making myelin, the sheath around nerve fibres, and in producing neurotransmitters. So people take it hoping for clearer thinking, and often for more energy and a steadier mood, usually with no outright deficiency behind the complaint.
What research has found. A meta-analysis of sixteen randomised trials and over six thousand adults measured attention, memory and other domains of thinking, and found no difference between B12 and placebo in any of them. Measures of low mood came out the same way; only one trial had looked at everyday tiredness, too few to pool. A later trial in older adults with mild memory trouble reported results only for B12 taken with folic acid. A fair body of trials has looked at this, and most point the same way.
Nerve pain and sensation
The thinking. A long shortage of vitamin B12 is linked with nerve fibres losing their coating and with peripheral neuropathy: numbness, tingling or burning in the hands and feet. The vitamin is involved in making that coating, which is the thinking behind taking it when nerves play up; people on metformin for years come to it most often.
What research has found. One randomised trial followed ninety adults with type 2 diabetes who had taken metformin for four years or more and had nerve symptoms; half took a milligram of methylcobalamin daily for a year. Against placebo, nerve conduction, sweat-gland function, pain scores and quality-of-life ratings all improved, while two of the measures used did not change significantly. Few studies have measured this yet, so there is little to go on either way.
Blood sugar
The thinking. Vitamin B12 and blood sugar keep company because of metformin: the first-choice tablet for type 2 diabetes is the one most often linked with B12 drifting down. That raises an obvious question: does putting the vitamin back change how the body handles sugar?
What research has found. One small trial split eighty adults with type 2 diabetes, all already on tablets for it, into four groups; one took 500 micrograms of methylcobalamin a day on top. After eight weeks that group’s longer-term blood sugar measure, insulin and insulin resistance had all improved against standard care alone, while blood fats were unchanged in every group. Very little research has measured this so far, either way.
Pregnancy and early life
The thinking. Reviews describe low vitamin B12 as a worldwide public health problem that falls hardest on pregnant women and young children. Since the vitamin has a hand in DNA, in the making of red blood cells and in folate chemistry, researchers have asked whether topping it up early changes how a baby grows and develops. Much of that work was done in pregnancies where a quarter to a half of the women were already short of it.
What research has found. Reviews pooling trials in pregnancy and in children under twelve, plus trials in Nepal and Bangladesh, measured birth weight, length of pregnancy, height, development scores and anaemia. Supplements reliably raised B12 levels in mothers, breast milk and children, and cut the number of children counted as deficient; on growth, development and anaemia most found little to no difference. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
What does vitamin B12 do in the body?
Vitamin B12 is a coenzyme: a helper an enzyme cannot work without. It holds two such posts, one in the main body of the cell, where an enzyme turns homocysteine into methionine, and one in the mitochondria, the cell’s power plants. Through those two reactions it has a hand in copying DNA, in the body’s many methylation reactions, in forming red blood cells and in building myelin.
When it runs short, both reactions slow and their raw materials pile up, which is why homocysteine and methylmalonic acid are measured alongside B12 itself. Reviews are frank that a single blood reading tells you less than people assume: a low figure need not mean a shortage, and a real one has turned up in people whose reading looked normal. Some gut bacteria make B12, but little of it is thought to reach us.
What do people say about taking vitamin B12?
These are anecdotes people have shared, not evidence.
What people like
- Tiredness lifting is by far the commonest report: less washed out, better concentration, usually within a fortnight.
- Often, pins and needles or numbness in the hands and feet eased, and a few mention palpitations settling.
- Some describe the change, once their level came back up, as night and day, usually after years of being low.
- A mouth spray or a tablet dissolved under the tongue is often what finally worked after swallowed tablets did nothing.
- A minority mention hair and mood picking up too, though nearly always alongside iron, folate or vitamin D.
Common complaints
- Very commonly, people say swallowed tablets did nothing and blame absorption; several had that confirmed and moved to injections.
- Often, people feel good for a few weeks after an injection, then slide back long before the next is due.
- Some report their level came up on paper while they still felt exhausted, and looked elsewhere: iron, thyroid, the perimenopause.
- Cost comes up wherever people go private: a single injection quoted at roughly £20 to £50, tablets a few pounds a month.
- A minority mention discomfort rather than side effects: injections that sting, patches or sprays they doubted were doing anything.
How people take it
- A 1,000 microgram tablet once a day is the usual starting point, given two or three months before a retest.
- Very commonly, anyone who doubts they absorb tablets moves to a spray or one dissolved under the tongue, to skip the stomach.
- The form is argued about: the methyl form most often suggested, the cyano form most often blamed for doing little.
- Some take folate or a B-complex alongside it, several iron or vitamin D for symptoms that overlap.
- A minority use skin patches, or inject themselves with ampoules bought abroad, when the gap between prescribed injections felt too long.
Read from these public discussions:
- Vitamin b12 deficiency (Mumsnet, 2023)
- Anyone with Vit B12 deficiency? (Mumsnet, 2023)
- B12 (Mumsnet, 2024)
- Anyone tried vitamin b12 patches? Do they work? (Mumsnet, 2022)
- B12 supplements; side effects? (Mumsnet, 2011)
What forms of vitamin B12 are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| Methylcobalamin | Cobalamin carrying a methyl group; the form used in two of the trials on this page. | 100 µg to 1 mg |
| Cyanocobalamin | Cobalamin carrying a cyanide group; like every form of B12, it is grown by fermentation. | 500 µg to 1 mg |
| Adenosylcobalamin | Cobalamin carrying an adenosyl group; labels sometimes call it dibencozide instead. | not in our price tables yet |
| Hydroxocobalamin | Cobalamin carrying a hydroxyl group; the form given by injection in inherited cobalamin disorders. | not in our price tables yet |
| Form not stated | The label says vitamin B12 without naming which cobalamin is inside. | 20 µg to 1 mg |
What else is worth knowing about vitamin B12?
- Labels give the amount per serving in micrograms, and a serving may be more than one tablet; the form is usually, not always, named.
- Doses varied hugely: 0.9 to 150 micrograms a day in the children’s trials, 5 to 250 in pregnancy, 500 to 1,000 in the diabetes trials.
- Side effects were barely reported: no trial in the children’s review recorded any, and of those comparing tablets with injections, one reported none and another had two people in thirty leave early.
- The studies behind this page were nearly all in particular groups: pregnant women and children where low levels are common, older adults with mild memory trouble, adults on long-term metformin.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (17 studies)
- Efficacy of different routes of vitamin B12 supplementation for the treatment of patients with vitamin B12 deficiency: A systematic review and network meta-analysis. (2024, systematic review)
- Oral vitamin B<sub>12</sub> versus intramuscular vitamin B<sub>12</sub> for vitamin B<sub>12</sub> deficiency. (2018, systematic review)
- Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression. (2021, meta-analysis)
- Effects of Folic Acid and Vitamin B12, Alone and in Combination on Cognitive Function and Inflammatory Factors in the Elderly with Mild Cognitive Impairment: A Single-blind Experimental Design. (2019, randomised trial)
- Vitamin B12 Supplementation in Diabetic Neuropathy: A 1-Year, Randomized, Double-Blind, Placebo-Controlled Trial. (2021, randomised trial)
- Folic acid and vitamin B12 supplementation in subjects with type 2 diabetes mellitus: A multi-arm randomized controlled clinical trial. (2020, randomised trial)
- Vitamin B12 supplementation for growth, development, and cognition in children. (2026, meta-analysis)
- Vitamin B12 supplementation during pregnancy for maternal and child health outcomes. (2024, systematic review)
- Maternal Vitamin B12 Status During Pregnancy and Its Association With Outcomes of Pregnancy and Health of the Offspring: A Systematic Review and Implications for Policy in India. (2021, systematic review)
- The effect of vitamin B12 supplementation during pregnancy on infant growth and development in Nepal: a community-based, double-blind, randomised, placebo-controlled trial. (2023, randomised trial)
- Vitamin B12 supplementation during pregnancy and postpartum improves B12 status of both mothers and infants but vaccine response in mothers only: a randomized clinical trial in Bangladesh. (2016, randomised trial)
- B Vitamins in the nervous system: Current knowledge of the biochemical modes of action and synergies of thiamine, pyridoxine, and cobalamin. (2020, review)
- Vitamin B12 as a modulator of gut microbial ecology. (2014, review)
- Microbial production of vitamin B 12 : a review and future perspectives. (2017, review)
- Long-term metformin therapy and vitamin B12 deficiency: An association to bear in mind. (2021, review)
- Guidelines for diagnosis and management of the cobalamin-related remethylation disorders cblC, cblD, cblE, cblF, cblG, cblJ and MTHFR deficiency. (2017, review)
- Biomarkers and Algorithms for the Diagnosis of Vitamin B12 Deficiency. (2016, review)
How much does vitamin B12 cost?
That depends on the form and the pack, so we work out the price of the same dose of every vitamin B12 product we can find and rank them.