Vitamin B12 Dosage – How Much Then?
If you ask around for the correct dosage of vitamin B12, you will soon discover there are a variety of suggestions. Different studies reach very different conclusions ranging from suggestions of 3 µg right up to 1000 µg. So how much vitamin B12 should you be taking? What’s the right dosage for you?
The daily requirement of vitamin B12 is estimated to be around 1.5 – 2 µg, but intake needs to be higher than this because not all the vitamin B12 in foods or from supplements can be absorbed by the body. Because of this, the official recommendation from the WHO is 2.4 µg of vitamin B12 per day. However, more and more often, recommendations for dosages are considerably higher than this figure. How can these differences in opinion be explained?
Vitamin B12 Dosage Chart
There are fundamentally five different categories for dosages of vitamin B12, which each apply to different specific health circumstances.
(low supplementary requirement)
Insurance for good health with provision of roughly half of the daily requirement
(full supplementary requirement)
Coverage of the whole daily requirement in healthy people
Coverage of the daily requirement even in cases of absorption problems
To help cure disease and to replenish the body’s B12 storage
5.000 – 10 .000 µg
Treatment of diseases
Dependent on individual cases
Vitamin B12 Dosage and Absorption
How have the very different needs in the cases outlined above been established? The apparent mystery of which advice to follow can be easily resolved if you have a better understanding of how the body absorbs vitamin B12. For convenience, we will firstly concentrate on absorption via digestion and then at the end resorption via the oral mucosa, the mouth’s mucus membrane, before looking at vitamin B12 injections.
Vitamin B12 that is administered through food or via an oral supplement can be absorbed in two different ways:
- Via the transport protein known as the intrinsic factor (IF) in the small intestine
- Through passive diffusion in the oral mucosa and small intestine
The absorption capacity of the intrinsic factor is a maximum of between 1.5 – 2 µg per dose or meal. This capacity is because there is a limited number of special receptors in the intestine, which are responsible for absorption of the vitamin B12 and intrinsic factor complex. The aforementioned 1.5 – 2 µg of vitamin B12 can only be absorbed in one go. After a few hours, however, the receptors are fully restored and ready to absorb a further dose of vitamin B12.
If a large quantity of B12 has been supplied, some of this may also be absorbed via passive diffusion through the intestinal wall and into the blood stream. However, this is only around one to two percent of the dose, as the rest is simply excreted.
Calculating Dosages of Vitamin B12
The absorption of vitamin B12 can be calculated as follows:
Absorption = 1.5 + dose/100
The initial 1.5 µg stands for the absorption via the intrinsic factor, whilst the second part explains the percentage absorbed through passive diffusion.
Therefore, a 200 µg dose would result in: 1.5 µg + 200/100 µg = 3.5 µg
These calculated absorption levels can, however, be dramatically reduced by digestive disorders. Further details on this can be found in our article on malabsorption.
Vitamin B12 Dosages: Single Dose or Several?
Another factor to be considered with regard to vitamin B12 dosage levels is whether to opt for a single dose or several smaller doses.
Our bodies are accustomed to smaller doses that are distributed throughout the day, which caters to the 1.5 – 2 µg absorption capacity of the intrinsic factor.
Two doses of just 3 µg results in the same total absorption as one single dose of 150 µg:
Multiple 3 µg dose: 2 x 1.5 µg = 3 µg
Single 150 µg dose: 1.5 + 150/100 µg = 3 µg
If you would prefer to take your vitamin B12 in smaller doses, then three small doses across the day is perfect. For those who would rather take one dose in the day, a much higher dosage level is required because the absorption via passive diffusion becomes very important.
High Dosage Vitamin B12
A very high dose can cover the body’s requirement for a few days. For example, American doctors currently recommend taking 2000 µg, once a week. This way, the body can be covered for the entire weekly requirement:
1.5 µg + 2000/100 µg = 21.5 µg
Whether this method of administering high dosage bursts of vitamin B12 is really advisable is often questioned by naturopaths. They instead recommend a steady intake of vitamin B12 in small or moderate doses. This allows blood levels to remain constant, which is what the body and excretory organs (liver and kidneys) would experience in an optimal, natural setting.
Vitamin B12 Dosages For Different Uses
With knowledge of the vitamin B12 absorption mechanisms, the seemingly contradictory advice on dosages in the table below can be better understood.
Number of doses
Calculated quantity of vitamin B12
Intervals throughout the day
IF + passive diffusion
1 – 3 µg
10 µg supplements
IF + passive diffusion
1 – 2 µg
Current studies on healthy people3
4 – 7 µg
Intervals throughout the day
IF + passive diffusion
2 – 4 µg
Current studies on anemic patients 4
500 – 600 µg
5 – 6 µg
Despite variations in the recommended doses above, the calculated amount of vitamin B12 absorbed is pretty constant. The residual differences can also be easily explained.
Anemic patients have a higher requirement because of the damaging effect that the disease has on their passive diffusion capabilities.
The discrepancy between the values recommended by the DGE and current studies on healthy people is probably due to the fact that the DGE’s research shows little in the way of calculated quantities based on absorption levels, unlike that of current studies.
How Much Vitamin B12 do I Need?
Answering the question ‘how much do I need?’ is difficult to do with precision when it comes to vitamin B12. Rather than attempting this, ask yourself the following:
- How should my vitamin B12 be supplied (one large single dose or several smaller ones)?
- How well can my body utilize vitamin B12?
The following table shows current dosage suggestions according to various studies. The dosages are intended to completely cover the daily requirement alone.
The table shows appropriate dosages, taking into consideration aspects that may affect absorption. For example, alcohol consumption, medication use and digestive problems are all common hinderances of vitamin B12 absorption. The elderly are most frequently affected by the latter, as only small, insufficient quantities can be absorbed.
Means of absorption
IF and passive diffusion
150 – 250 µg
3 x 2 – 5 µg
Medication, heavy alcohol use5
IF and passive diffusion both restricted
250 – 500 µg
After operation on digestive system or with absorption disorders6,7
IF and passive diffusion both restricted
IF and passive diffusion both restricted, IF severely so
500 – 1000 µg
IF completely shut down, passive diffusion restricted
500 – 1000 µg
An administration of several smaller doses only really makes sense for healthy people, for whom the intrinsic factor absorption mechanism is in full working order. For anyone with a form of digestive disorder, this method is insecure; meaning most opt for larger single doses so that maximum absorption can take place via passive diffusion.
What is a Good Dosage of Vitamin B12?
A good average dose, for people who are in otherwise good health and have good absorption capabilities, lies in the region of 150 – 250 µg for a single dose. This will cover the body’s daily requirement.
People with an increased need or absorption difficulties are advised to take a higher dosage of 300-500 µg. This dose is also sufficient in preventing a deficiency even if absorption via the intrinsic factor is impossible.
Those who only consume meat or dairy in moderation and wish to take vitamin B12 as an additional dietary supplement should take a low dose of 3 – 50 µg. It is recommended to calculate how much vitamin B12 is theoretically absorbed from your typical dietary intake, as sometimes supplements can actually be unnecessary. However, in cases of high stress, environmental pressures and inflammation of the digestive tract, an extra dose of vitamin B12 could be required.
The elderly and anemia patients should seek the advice of a doctor before choosing the right supplement, as 350 µg of vitamin B12 could be considered too low. At present, a long-term supplement is recommended for the elderly because absorption capabilities are severely diminished and a normal diet can no longer meet the body’s needs. In many cases, high doses of 1000 – 3000 µg are prescribed.
Vitamin B12 Overdose
Since vitamin B12 is generally considered harmless and hardly any negative side effects of it are known, a vitamin B12 overdose is essentially impossible. However, it is sometimes advisable to err on the side of caution with regard to dosage levels. It is generally argued that what the body doesn’t need, it will simply excrete. As already noted, in the USA, vitamin B12 supplements with dosages of 1000 µg are very common and in Germany, doses of even 2000 µg are generally considered to be harmless.
However, it is important not to go overboard. A dosage of between 150 and 500 µg a day is the optimum amount of most people and higher dosages only really make sense for medicinal or therapeutic purposes. As previously stated, absorption in smaller doses is certainly gentler and more comfortable for the body.
Dosages of Vitamin B12 Injections
The digestive system is completely bypassed when using B12 injections, meaning the body’s complex absorption mechanism no longer plays a role. The vitamin is injected directly into the muscle and then carries on to the bloodstream. In this process, between 40 and 70% of the active ingredient in the dose can be used by the body, which can meet its requirements for weeks or sometimes months. For this reason, high doses are often injected in large time intervals to optimize convenience and comfort. It is possible to administer just four high dosage injections a year to meet the body’s annual B12 needs. For a more details account on vitamin B12 injection dosages, please refer to our article on the subject.
Vitamin B12 via the Oral Mucosa
Vitamin B12 can also be absorbed by the oral and nasal mucosa, which is why vitamin B12 lozenges, vitamin B12 drops and sprays and even occasionally vitamin B12 nasal sprays are available.
For these to be fully utilized, the B12 should remain in the mouth for as long as possible and be in contact with the oral mucosa. The efficiency of absorption via the oral mucosa is similar to that of the small intestine, although it is unclear as to how much of the B12 that is swallowed ultimately makes its way to the intestine.9,10
To date, no studies have indicated particular advantages or disadvantages in using the sublingual route instead of the digestive tract. The dosage and effectiveness of both appears to be equal.
One particular benefit of these dosage forms is the comfort and ease of use involved.
As is often the case, the truth probably lies somewhere in the middle. Whilst vitamin B12 supplements from the drugstore sometimes display no more than 3 µg, high dosage vitamin B12 supplements of 1000 µg are used regularly as a useful tool in therapeutic environments.
250 µg is still a very high dosage of vitamin B12 – particularly when compared with its natural occurrence in B12-rich foods, which typically contain 3 – 5 µg /100g – but it can be useful for meeting the body’s B12 requirement.
A repeated dose over the course of a day can allow for much lower dosage levels of around 2 – 5 µg, which are in line with the typical measures located in foods with a good B12 content.
As it is often impractical for most people to take a supplement several times throughout the day, a medium-sized single dosage of 150 – 250 µg a day seems to be the most practical and sensible solution.
1Deutsche Gesellschaft für Ernährung, Österreichische Gesellschaft für Ernährung, Schweizerische Gesellschaft für Ernährungsforschung, Schweizerische Vereinigung für Ernährung (Hrsg.) „Referenzwerte für die Nährstoffzufuhr“ 1. Auflage, 5., korrigierter Nachdruck, DGE, Bonn 2013 http://www.dge.de/modules.php?name=Content&pa=showpage&pid=3&page=7
3Mustafa 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.
4Berlin, 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
5ANDRÈS, 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
6Barbara 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
7C. 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.
8Eussen 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.
9Sharabi, 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
10Georges 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.