Vitamin B12 Dosages – What is Correct?
Anyone who has made investigations into the correct vitamin B12 dosage will know how varied the recommendations can be: the span ranges from 3 µg to 1000 µg of B12 and various studies come to different conclusions. So what information is correct? What dosage of B12 do you need to take to reap the multiple benefits of this vital vitamin?
The human body’s daily requirement of B12 is considered to be between 1.5 – 2 µg, although the intake itself must be slightly higher, as not all B12 can be absorbed from food sources or supplements. The current recommendation is therefore 2.4 µg of B12 per day (1).
Nonetheless, recommendations are often given that are much higher – how can these differences be explained?
Vitamin B12 Dosages: Treatment or Supplementation?
First and foremost, we need to distinguish between the two main applications of vitamin B12:
- Vitamin B12 treatment: initial therapy following a B12 deficiency or due to illness
The aim is to replenish the body’s store of the vitamin and raise the blood level.
Recommended dose: 1000µg/day for 3-6 months or 5000µg/day for 4 weeks
- Dietary supplementation: prevention and maintenance doses
The aim is to cover the daily requirement and to keep the B12 supply stable.
Recommended dose: depending on the individual between 10 – 1000 µg/day.
Vitamin B12 Deficiency Treatment – When and Why?
In the case of an acute vitamin B12 deficiency or obvious deficiency symptoms, vitamin B12 treatment is recommended as an initial therapy to quickly raise blood levels and replenish the body’s stores.
In many cases this is done with injections, since most professionals believe that this method allows for a much higher intake than oral therapy. Numerous studies have shown however that taking vitamin B12 orally as a treatment can have just as good results.
When: in the case of a confirmed B12 deficiency or when symptoms are clear (to verify deficiency it is worth taking a vitamin B12 test).
Dose: either: 1000 µg per day (it is recommended divided into two smaller doses of 500 μg, as this results in a higher absorption rate – see below)
or: 5000 µg per day.
Period: 1000 µg for 3-6 months or 5000 µg for 4 weeks.
For more information on B12 treatment with injections, click here.
Dosage Profile for Vitamin B12 Supplementation
The various different vitamin B12 dosages can be split in five profile groups:
|Purpose||Profile||Recommended Daily Dose|
(Children, low additional dietary requirement)
|For adults in good health, this dose covers approx. half of the daily requirement|
(adult full daily requirement)
|Covers the total daily requirement for those in good health||250 µg|
(pregnant women, those with an increased daily requirement)
|Covers the daily requirement for those who need an additional B12 supply||500 µg|
(lactating women, older people, those with a significantly increased requirement)
|Covers the daily requirement for those with a significantly increased need and absorption disorders||1000 µg|
(initial therapy, specialist application)
5000 – 10 000 µg
In addition to treatment of disease and as a B12 intensive therapy to rapidly replenish the body’s B12 stores
Vitamin B12 Dosages for Babies, Children and Adults
Recommended Dietary Allowance
0 – 6 months, breastfed
supply through breastmilk
0 – 6 months, not breastfed
6 – 12 months
3-5 µg /day
1 – 3 years
|5-10 µg /day|
100 µg every 2 days
4 – 8 years
10 µg /day
9 – 13 years
50-100 µg /day
14 – 18 years
100 µg /day
Teenagers and Adults
From 13 years
250 – 500 µg /day
500 µg /day
500 – 1000 µg /day
*According to the Institute of Medicine (IOM, now National Academy of Medicine)
**For average dosages for those with an increased requirement – see above. See the following for details on the actual intake of B12
Vitamin B12 Dosages and Absorption
Where do these many different recommendations come from? The disparities are easily understood by looking more closely into the research and understanding how vitamin B12 is absorbed in the body. For the sake of simplicity, we will first concentrate on digestive absorption, before taking a look at absorption via the oral mucosa and B12 injections.
Vitamin B12, supplied via food or oral supplements, can be absorbed by the body in two different ways (4):
- Through the transport protein called intrinsic factor in the small intestine
- Through passive diffusion in the mucosa membranes of the mouth and small intestine
The maximum absorption ability through the intrinsic factor is somewhere between 1.5 – 2 µg per meal. This is because the complex of B12 and intrinsic factor is absorbed via a limited number of special receptors in the intestinal mucosa. As a result, only the mentioned 1.5 – 2 micrograms of B12 can be absorbed at once; only after a few hours are the receptors available again to take in more of the vitamin.
However, if a large amount of B12 has been consumed, a large proportion of it passes through the intestinal wall into the blood via passive diffusion – but this is only at a rate of approximately one to two percent of the dose (the rest is excreted).
Vitamin B12: Calculated Dosages
The intake of B12 can be calculated as follows:
Intake = 1.5 + dose/100
The first 1.5 µg represent the intake via the intrinsic factor; the second part, via passive diffusion. With a dosage of 200 µg the intake would be: 1.5 µg + 200/100 µg = 3.5 µg. This calculated intake can nonetheless be significantly compromised as a result of various absorption disorders, further explored in our article: Vitamin B12 Malabsorption
Single Dose or Multiple Doses?
An important factor in the dosage of B12 is whether the supplement is administered in a single dose or in several small doses. Biologically-speaking we are adapted to several small doses of B12, which are consumed throughout the day, whereby each time 1.5 – 2 micrograms of the vitamin is absorbed via the intrinsic factor.
Two doses of 3 μg each lead to the same total uptake as a single dose of 150 μg:
Multiple doses of 3 μg: 2 x 1.5 μg = 3 μg
Single dose of 150 μg: 1.5 + 150/100 μg = 3 μg
If you would rather cover your vitamin B12 requirement with small doses, it is best to split your intake into three. In contrast, if you prefer to take a single dose, the dose must be much higher, as here the passive diffusion of the vitamin is the pivotal process.
High Dose Vitamin B12
A very large dose can cover the B12 requirement for several days. Especially in America, for example, many doctors recommend taking 2000 μg per week: 1.5 μg + 2000/100 μg = 21.5 μg
Some naturopaths doubt whether this large weekly intake is really advisable. Instead they recommend a steady supply of B12 in moderate doses. This keeps the blood level constant in a natural range, which is gentler on the body, especially for the liver and kidneys.
Vitamin B12 Dosages for Different Applications
With this knowledge in mind, all apparent contradictions of the different B12 dosages are suddenly resolved. Let’s take a look at them.
|Recommended by||Recommendation||Intake Method||Mechanism||Calculated B12 Intake|
|Institute of Medicine (IOM) (1)||2.4 µg||multiple doses over the day||IF + passive diffusion||1 – 2.4 µg|
|Vegan Society (2)||supplement 10 µg||single dose||IF + passive diffusion||1 – 2 µg|
|Current Studies on Healthy People (3)||4 – 7 µg||multiple doses over the day||IF + passive diffusion||2 – 4 µg|
|Current Studies on Anaemic Patients (4)||500 – 600 µg||single dose||passive diffusion||5 – 6 µg|
Despite the different dosages, it is striking that the amounts of B12 absorbed in the end are very similar to one another. The remaining differences can also be explained quite simply: for example, the greater need for anemia patients, by the fact that not only is the intrinsic factor switched off, but their ability for passive diffusion is diminished.
The discrepancy between the values of the IOM and those of recent studies on healthy people may be explained by the fact that the former represent minimal arithmetic values that assume an optimal uptake in completely healthy people, whereas the current studies represent practically determined values, which take into account real-life fluctuations.
How Much Vitamin B12 do I Need?
There is no one answer to this question. Instead it must be determined individually, taking into account the following factors:
- How the B12 is administers (one large single dose or multiple small doses?)
- How well the body can absorb and utilise B12
The following matrix shows current dosage recommendations for B12 supplements according to various studies. It is assumed that the dose should cover the entire daily requirement alone. The matrix shows what dose is needed if certain impairments are present e.g. high alcohol consumption, medication and gastrointestinal problems (very common in older people).
|Group||Explanation||Single dose||Multiple doses|
|Healthy people||IF + passive diffusion||150 – 250 µg||3 x 2 – 5 µg|
|Intake of medication/high quantities of alcohol/drugs (5)||restricted IF + passive diffusion||250 – 500 µg||non-effective|
|Following gastrointestinal operations/in the case of gastrointestinal disorders (6, 7)||very restricted IF + passive diffusion||500 µg||non-effective|
|Older people (8)||very restricted IF + passive diffusion||500 – 1000 µg||non-effective|
|Anaemic patients (4)||IF completely disabled + restricted passive diffusion||500 – 1000 µg||non-effective|
An intake of several small doses only makes sense in healthy people, in which the intake through the intrinsic factor is full or adequate. When there are any absorption problems present, this absorption pathway is high unpredictable, which is why large dosages rely on passive diffusion.
What is a Sufficient Dosage of Vitamin B12?
A medium dose, covering the daily requirement for completely healthy individuals, thus lies between 150 – 250 μg in a single administration.
In the case of an increased need or slight absorption disorder, an increased dosage in the range of 300 – 500 μg is recommended. This dose would be sufficient to prevent a deficiency through passive diffusion alone.
Anyone who eats meat and dairy products only in moderation and therefore wants to take vitamin B12 supplements, requires a small dose between 3 – 50 micrograms per day, depending on their state of health and nutrition. Here a projection can help determine the maximum amount of B12 which is absorbed through the diet, as in some cases supplements are superfluous. However, in circumstances of high stress, environmental pollution or gastrointestinal problems, an undersupply can emerge.
For many older people and anaemic patients, 350 μg is the absolute lower limit of the B12 dosage range, according to cited studies. Here, however, a doctor should always be consulted. A permanent B12 supplementation is often recommended, especially in the elderly, as the ability to absorb the vitamin decreases greatly with age and can thus not be obtained through the diet alone. In such cases, B12 is often administered in high doses between 1000 and 3000 μg.
Moreover, for further details on which vitamin B12 active ingredient to choose, see our article: Vitamin B12 Forms
Vitamin B12 Overdose
Since vitamin B12 is considered harmless and hardly any negative side effects of an overdose of the vitamin are known, some experts recommend “playing it safe” when it comes to B12. The logic here is that what the body does not need, it will excrete. As a result, in the USA, many B12 supplements contain dosages of 1000 μg; in Germany, supplements of up to 2000 μg are classified as harmless by all experts.
However, we believe that there is no need to exaggerate: doses between 150 – 500 μg a day ensure an optimal B12 supply in most people. Higher doses only make sense in a medical or therapeutic context. Furthermore, as we explored above, an intake of small doses is gentler on the body.
Vitamin B12 Injection Dosage
In the case of B12 injections, the route through the intestine (via intrinsic factor) is bypassed; the vitamin is injected directly into the muscle and thus directly into the blood stream. Depending on the active ingredient, 40 – 70 % of the dose is absorbed by the body, which can cover the B12 requirement for weeks or even months. High doses are often injected at long intervals to keep costs down. It is possible to cover the B12 requirement with only 4 high dose injections per year. For a detailed description of the dosage of B12 through injection, please see our detailed article on the subject.
Vitamin B12 Through the Oral Mucosa
Vitamin B12 can also be absorbed through the oral and nasal mucosa, which is why it is also available in the form of lozenges, drops/sprays and (very rarely) as nasal spray. To make full use of this mechanism, the B12 should be kept in the mouth for as long as possible, to take effect on the mucous membranes.
The effectiveness of B12 absorption via the oral mucosa is similar to that via the intestine. It remains unclear, however, how much B12 absorbed via swallowing is actually just absorbed in the intestine (9, 10). The superiority/inferiority of the sublingual route over the digestive route has not been fully researched – the dosage and efficacy seem to be the same in both cases. However, the key advantage of this form is above all the ease of administration.
Whilst B12 supplements from the chemist, containing a very low B12 dosage, might be optimal for everyday use; high dose B12, with over 1000 micrograms, can be incredibly effective in certain therapeutic circumstances. As with most things, the key lies in the context.
A dosage of 250 μg is still very high – especially considering that the average content in B12-rich foods is 3-5 μg per 100g. Such a high dose makes sense, however, if the total B12 requirement is to be met via a single administration. When B12 is taken multiple times throughout the day, 2-5 µg of B12 per intake can be sufficient. This method mirrors a natural dietary intake.
Since for most people it is impractical to take supplements several times a day, a single dosage of 250-500 micrograms seems to be the best solution.
- Institute of Medicine, Food and Nutrition Board, National Academies of Science, Dietary Reference Intakes (DRI): Recommended Dietary Allowances and Adequate Intakes, USA 2018, http://www.nationalacademies.org/hmd/~/media/Files/Activity%20Files/Nutrition/DRI-Tables/5Summary%20TableTables%2014.pdf?la=en
- Mustafa Vakur Bor, Kristina M von Castel-Roberts, Gail PA Kauwell, Sally P Stabler, Robert H Allen, David R Maneval, Lynn B Bailey Ebba Nexo „Daily intake of 4 to 7 µg dietary vitamin B-12 is associated with steady concentrations of vitamin B-12–related biomarkers in a healthy young population“ Am J Clin Nutr 2010 91: 3 571-577; First published online January 13, 2010. doi:10.3945/ajcn.2009.28082.
- Berlin, H., Berlin, R. and Brante, G. (1968), ORAL TREATMENT OF PERNICIOUS ANEMIA WITH HIGH DOSES OF VITAMIN B12 WITHOUT INTRINSIC FACTOR. Acta Medica Scandinavica, 184: 247–258. doi: 10.1111/j.0954-6820.1968.tb02452.x
- ANDRÈS, E., DALI-YOUCEF, N., VOGEL, T., SERRAJ, K. and ZIMMER, J. (2009), Oral cobalamin (vitamin B12) treatment. An update. International Journal of Laboratory Hematology, 31: 1–8. doi: 10.1111/j.1751-553X.2008.01115.x
- Barbara M Rhode et al. Treatment of Vitamin B12 Deficiency after Gastric Surgery for Severe Obesity. Obesity Surgery May 1995, Volume 5, Issue 2, pp 154-158
- C. Poitou Bernert, C. Ciangura, M. Coupaye, S. Czernichow, J.L. Bouillot, A. Basdevant, Nutritional deficiency after gastric bypass: diagnosis, prevention and treatment, Diabetes & Metabolism, Volume 33, Issue 1, February 2007, Pages 13-24, ISSN 1262-3636, http://dx.doi.org/10.1016/j.diabet.2006.11.004.
- Eussen SM, de Groot LM, Clarke R, et al. Oral Cyanocobalamin Supplementation in Older People With Vitamin B12 Deficiency: A Dose-Finding Trial. Arch Intern Med. 2005;165(10):1167-1172. doi:10.1001/archinte.165.10.1167.
- Sharabi, A., Cohen, E., Sulkes, J. and Garty, M. (2003), Replacement therapy for vitamin B12 deficiency: comparison between the sublingual and oral route. British Journal of Clinical Pharmacology, 56: 635–638. doi: 10.1046/j.1365-2125.2003.01907.x
- Georges Delpre, Pinhas Stark, Yaron Niv, Sublingual therapy for cobalamin deficiency as an alternative to oral and parenteral cobalamin supplementation, The Lancet, Volume 354, Issue 9180, 28 August 1999, Pages 740-741, ISSN 0140-6736, http://dx.doi.org/10.1016/S0140-6736(99)02479-4.