Vitamin B12
Cobalamin, a B vitamin
A B vitamin, also called cobalamin, found in meat, fish, milk, cheese and eggs, and sold as cyanocobalamin, methylcobalamin and hydroxocobalamin. This page covers only studies in people that measured thinking, memory, mood, stress, sleep, energy, tiredness or quality of life. It is not all research on vitamin B12. Here is every such study we could find, sorted from each study's summary.
- Found in: meat, fish, milk, eggs
- Most tested: 1,000 µg a day
- Often given by injection or in deficiency
From every paper to the studies that matter
Most research on vitamin B12 is about blood levels, diet or deficiency. This page counts only the studies that gave vitamin B12 to people and measured thinking, memory, mood, stress, sleep, energy, tiredness or quality of life, so the count is not all research on the vitamin.
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3,783 papers mention vitamin B12 and these topics.Every record in PubMed, all years
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658 are about people.The rest: 353 lab and animal studies, 701 reviews, 2,071 on chemistry, farming and more
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77 give vitamin B12 on its own.110 more give it inside a blend, such as a B complex or multivitamin
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24 are randomised against a placebo.Randomised controlled trials In a randomised controlled trial, people are put into groups by chance, one taking the treatment and one a placebo or other comparison. Chance spreads differences such as age and health evenly, so a difference between the groups is more likely to be down to the treatment., the strongest kind of study
Bar lengths use a square-root scale so the small numbers stay visible.
How much research there is
- 77 studies giving vitamin B12 to people and measuring these topics
- 24 of them randomised against a placebo A placebo-controlled trial compares a real treatment with a dummy that looks the same, the placebo. People often feel better when they expect to, so comparing against a placebo shows how much of the change comes from the treatment itself.
- 8,862 people taking part, where studies say
- 151 systematic reviews A systematic review searches for every study on a question in a set, written-down way, judges the quality of each and sums up what they show together. Many include a meta-analysis. The Atlas lists these as pooled reviews. pooling the trials
Studies in people, by year published
Vitamin B12 on its own, in studies that measured thinking, memory, mood, stress, sleep, energy, tiredness or quality of life.
What the studies looked at
Each study can measure several things. Choose a topic to see its studies in the list below.
Studies in people with a diagnosed condition are counted here and listed with their population. We describe what they measured, not what they might treat. Most studies also report safety; see below.
What was tested, and how much
Doses are shown in micrograms (µg) a day. Many studies used injections or high oral doses of around 1,000 µg (1 mg), and the forms differ (cyanocobalamin, methylcobalamin, hydroxocobalamin), so doses are only roughly comparable. Weekly or monthly injections are averaged per day or shown as the single dose, which is why some dots sit far to the right. Many studies don't state a daily dose, so they have no dot.
Daily amount, one dot per study
Studies per extract
Named extracts are the maker's brand. "Not named" means the study didn't say.
All studies in people
Filter the list, then open a study on PubMed. Each row comes from the study's published summary. Many studies are in people with low B12 or a condition, not in healthy adults, and this page counts only those that measured the topics above. Studies giving B12 in a B complex or multivitamin are counted as blends but not listed.
| Study | Who took part | People | Extract and daily dose | Length |
|---|---|---|---|---|
| Field 2026RCT, placebo | General population adults, mostly female | 267 | Not named, 1,000 µg | 4 weeks |
| Reischl-Hajiabadi 2026Single-arm or open-label | Children with cobalamin C deficiency | 21 | Hydroxocobalamin | – |
| Agrawal 2024Single-arm or open-label | Adults with B12 deficiency anaemia | 180 | Not named | 6 weeks |
| Chandyo 2023RCT, placebo | Pregnant women and their infants, Nepal | 800 | Not named, 50 µg | – |
| Ulak 2023RCT, placebo | Nepalese infants, follow-up at preschool age | 600 | Not named, 2 µg | 52 weeks |
| Zhou 2023RCT, active or other control | Middle-aged and older adults with cognitive impairment | 115 | Methylcobalamin, 750 µg | 26 weeks |
| Wu 2023Observational | Young nitrous oxide users with neuropsychiatric disorders | 16 | Not named | – |
| Scalais 2023Single-arm or open-label | Early-onset cblC deficiency patients | 5 | Hydroxocobalamin | – |
| Goraya 2023Single-arm or open-label | Infants recovering from B12 deficiency | 3 | Not named | – |
| Hysing 2022RCT, placebo | Infants at risk of B12 deficiency, Nepal | 600 | Not named | 52 weeks |
| Field 2022RCT, placebo | Healthy young adults | 478 | Not named | 4 weeks |
| Liu 2022RCT, placebo | Older diabetics with low B12 | 59 | Not named | 117 weeks |
| Ueno 2022Single-arm or open-label | Older adults with B12 deficiency and cognitive impairment | 39 | Not named | – |
| Gharibpoor 2022Single-arm or open-label | Fibromyalgia patients | 30 | Not named, 1,000 µg | 7 weeks |
| Čorejová 2022Single-arm or open-label | Autistic children and young adults | 25 | Methylcobalamin, 500 µg | 29 weeks |
| Channer-Wallen 2022Single-arm or open-label | Healthy adults aged 25-50 | 14 | Cyanocobalamin, 3,000 µg | 2 weeks |
| Sashindran 2022Single-arm or open-label | Older adults with dementia and B12 deficiency | – | Not named | 12 weeks |
| Arendt 2021Observational | Danish registry patients with low or normal plasma B12 | 53,089 | Not named | – |
| D'souza 2021RCT, placebo | Adolescents pre-conception; offspring neurodevelopment | 557 | Not named, 2 µg | – |
| Vakilian 2021Non-randomised controlled | Alzheimer's patients with psychotic symptoms | 47 | Not named | – |
| Shoffel-Havakuk 2021Crossover, placebo | Professional singers without dysphonia | 20 | Cyanocobalamin, 1,000 µg | – |
| Kvestad 2020RCT, placebo | Children followed up at 6-9 years after infant supplementation | 791 | Not named, 2 µg | 26 weeks |
| Strand 2020RCT, placebo | Marginally stunted Nepalese infants | 600 | Not named, 2 µg | 52 weeks |
| Jatoi 2020Single-arm or open-label | Patients with B12 deficiency and mild cognitive impairment | 202 | Not named | 13 weeks |
| Wesół-Kucharska 2020Observational | Patients with cblA methylmalonic aciduria | 5 | Hydroxocobalamin | – |
| Ma 2019RCT, active or other control | Older adults with mild cognitive impairment | 240 | Not named | 26 weeks |
| Thomas 2019RCT, placebo | Children of mothers given B12 in pregnancy | 218 | Not named | – |
| van Campen 2019Single-arm or open-label | Adults with ME/CFS | 51 | Not named | 12 weeks |
| Serin 2019Single-arm or open-label | Children with neurological symptoms of B12 deficiency | 38 | Not named | 4 weeks |
| Scalais 2019Single-arm or open-label | Patients with intracellular cobalamin defects | 5 | Hydroxocobalamin | – |
| Scholten 2018RCT, placebo | IBS or IBD patients with fatigue | 95 | Not named, 1,000 µg | 8 weeks |
| Srinivasan 2017RCT, placebo | Infants of mothers given B12 in pregnancy | 366 | Not named, 50 µg | – |
| Kwok 2017RCT, placebo | Older diabetic adults with borderline low B12 | 271 | Methylcobalamin, 1,000 µg | 117 weeks |
| Vijayakumar 2017RCT, active or other control | Postmenopausal women with mild to moderate cognitive dysfunction | 56 | Methylcobalamin, 50 µg | 12 weeks |
| Vakilian 2017Non-randomised controlled | Alzheimer disease patients with psychosis on antipsychotics | – | Not named | – |
| Gupta 2016Non-randomised controlled | Adults with vitamin B12 deficiency | 13 | Not named | 6 weeks |
| Dangour 2015RCT, placebo | Older adults with moderate B12 deficiency | 201 | Cyanocobalamin, 1,000 µg | 52 weeks |
| Syed 2013RCT, active or other control | Depressed adults with low-normal B12 on antidepressants | 73 | Not named | 12 weeks |
| Kalita 2013Single-arm or open-label | Patients with B12 deficiency neurological syndromes | 33 | Not named | 26 weeks |
| Matos 2013Single-arm or open-label | Children with CblC deficiency | 5 | Hydroxocobalamin | – |
| van Dyck 2009Non-randomised controlled | Nursing home dementia, low vs normal B12 | 56 | Not named | 16 weeks |
| Kalita 2008Single-arm or open-label | Patients with B12 deficiency neurological syndromes | 36 | Not named | 13 weeks |
| Kwok 2008Single-arm or open-label | Dementia patients with B12 deficiency | 30 | Not named | 40 weeks |
| Eussen 2007RCT, placebo | Older adults with mild B12 deficiency | 195 | Not named, 1,000 µg | 24 weeks |
| Eussen 2006RCT, placebo | Older adults 70+ with mild B12 deficiency | 195 | Not named, 1,000 µg | 24 weeks |
| Aaron 2005Single-arm or open-label | B12 deficiency neurological syndromes | 63 | Not named | – |
| Osimani 2005Non-randomised controlled | Elderly dementia patients with low B12 and controls | 19 | Not named | 52 weeks |
| Hvas 2004RCT, placebo | Adults with raised methylmalonic acid | 140 | Not named | 12 weeks |
| Bolaman 2003RCT, active or other control | Megaloblastic anaemia from cobalamin deficiency | 60 | Cobalamin, 1,000 µg | 13 weeks |
| Bryan 2002RCT, placebo | Healthy women of various ages | 211 | Not named, 15 µg | 5 weeks |
| Abyad 2002Single-arm or open-label | Elderly with low B12 and cognitive dysfunction | 62 | Cyanocobalamin, 1,000 µg | 52 weeks |
| Ito 2001Non-randomised controlled | Alzheimer-type dementia patients on bright light | 28 | Not named | 4 weeks |
| van Asselt 2001Non-randomised controlled | Healthy elderly with low plasma cobalamin | 16 | Hydroxocobalamin | 22 weeks |
| Eastley 2000Non-randomised controlled | Memory clinic patients with low B12 | 88 | Not named | – |
| Nilsson 2000Single-arm or open-label | Dementia patients with cobalamin deficiency | 24 | Not named | – |
| Takahashi 1999RCT, active or other control | Patients with sleep-wake rhythm disorders | – | Methylcobalamin | – |
| Kwok 1998RCT, active or other control | Older Chinese adults with subnormal cobalamin | 50 | Cyanocobalamin | 17 weeks |
| Ali 1998Single-arm or open-label | Patients with low B12 and macrocytosis or neuropsychiatric signs | 43 | Not named | 26 weeks |
| Okawa 1997RCT, placebo | Patients with delayed sleep phase syndrome | 50 | Methylcobalamin, 3,000 µg | 4 weeks |
| Teunisse 1996Non-randomised controlled | Dementia patients with low B12 | 26 | Cobalamin | 26 weeks |
| Mayer 1996RCT, active or other control | Healthy adults | 20 | Cyanocobalamin and methylcobalamin, 3,000 µg | 2 weeks |
| Bohr 1996Non-randomised controlled | Healthy male shift workers | 10 | Methylcobalamin, 3,000 µg | 3 weeks |
| Cunha 1995Single-arm or open-label | Demented outpatients with B12 deficiency | 181 | Cobalamin | – |
| Carmel 1995Single-arm or open-label | Patients with low cobalamin, mostly demented | 16 | Cobalamin | – |
| Oren 1994RCT, placebo | Patients with winter seasonal affective disorder | 27 | Cyanocobalamin, 4,500 µg | 2 weeks |
| Meadows 1994Other | Case report, cognitive recovery with B12 | – | Not named | – |
| Martin 1992Single-arm or open-label | Elderly with low cobalamin and cognitive dysfunction | 22 | Cyanocobalamin, 1,000 µg | 26 weeks |
| Ikeda 1992Single-arm or open-label | Alzheimer-type dementia patients | 10 | Mecobalamin | – |
| Honma 1992Crossover, placebo | Healthy adults | 9 | Methylcobalamin, 3,000 µg | 4 weeks |
| Mishima 1992Single-arm or open-label | Demented patients with sleep-wake disorder | – | Methylcobalamin | – |
| Maeda 1992Other | Sleep-wake rhythm disorder patients in Japan | – | Not named | – |
| Regland 1991Single-arm or open-label | Dementia and pernicious anaemia patients | 18 | Not named | – |
| Okawa 1991Single-arm or open-label | Patients with sleep-wake rhythm disorders | – | Not named | – |
| Ohta 1991Single-arm or open-label | Adolescents with sleep-wake schedule disorders | – | Not named | – |
| Newbold 1989Non-randomised controlled | Patients with normal serum B12 | – | Hydroxocobalamin | – |
| Ellis 1973RCT, placebo | People with tiredness | – | Not named | – |
| Hughes 1970RCT, placebo | Elderly with low serum B12 | 39 | Not named | – |
What's known about safety
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In trials
A 2026 Cochrane review of 16 trials in children found no trials reported adverse effects when B12 was given alone against placebo, and one trial found little difference in side effects when it was added to other micronutrients. Doses ranged from 0.9 to 150 µg a day. A 2021 review of 16 trials in adults without advanced neurological disease or clear B12 deficiency found no effect on cognitive function or depression measures.
Larvie 2026, Cochrane review of 16 trials in 4,083 children; Markun 2021, review of 16 trials in 6,276 adults (abstracts)
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In the UK
Cyanocobalamin, hydroxocobalamin, 5'-deoxyadenosylcobalamin and methylcobalamin are on the permitted list of vitamin sources for food supplements. The NHS says adults need about 1.5 micrograms a day, and that taking 2 mg (2,000 micrograms) or less a day in supplements is unlikely to cause harm. It adds there isn't enough evidence to show the effects of high daily doses.
Annex II of Directive 2002/46/EC as retained in UK law (legislation.gov.uk); NHS vitamins and minerals, vitamin B12 page, reviewed Aug 2020
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Check first
The NHS says folic acid above 1 mg a day can mask the symptoms of vitamin B12 deficiency, which can eventually damage the nervous system if it isn't spotted and treated, and that this is a particular concern for older people. We found no source on B12 in pregnancy or breastfeeding, or with medicines, in the pages we opened. Speak to a pharmacist or doctor first if either applies to you, or if you take any medicine.
NHS vitamins and minerals, B vitamins and folic acid page; no other guidance opened, Oct 2026
Where these studies come from
We list every published study giving vitamin B12 to people that measured thinking, memory, attention, mood, stress, anxiety, sleep, energy, tiredness or quality of life. Cyanocobalamin, methylcobalamin, hydroxocobalamin and adenosylcobalamin count, by mouth, under the tongue, nasal or injection. Studies that only measure B12 levels, diet or genes are left out, as are studies where only the control group got B12. B12 added to a shared treatment and compared with that treatment alone counts as on its own. This first version is built from each study's summary; full-paper checks come next.
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We search
PubMed, the world's main library of medical research, for every paper on L-theanine.
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We keep studies in people
Lab and animal work is counted but left out of the list, because it doesn't tell you what happens in people.
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We note the basics
Who took part, how many, how much and for how long, from each study's published summary. A second check corrects what the first read gets wrong.
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We read them in full
Results appear once we've read the whole paper and checked every number. The date at the top shows when this entry was last updated.
Download the study list
Every study in people as a spreadsheet, 77 rows, free to reuse with a link back.
Versions
Each update to the data gets a new version number, so you can tell what changed and when.
See every version
1.0 · 24 Oct 2026. First release. Every published study giving vitamin B12 to people that measured thinking, memory, mood, stress, sleep, energy or quality of life is listed from its summary. None is read in full yet.
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