Vitamin B12 Daily Requirement
But what dosage of vitamin B12 do we require? And how much are we able to consume through foods? Does this amount differ for vegetarians and vegans? And when is it useful to take vitamin B12 supplements? This article aims to answer these questions and others regarding our requirement for vitamin B12.
Recommended Dietary Allowances (RDA) of Vitamin B12
The daily requirement of vitamin B12 is a value that cannot be clearly determined scientifically and must therefore be calculated according to various factors. This explains why internationally slightly different values are given for the recommended dietary allowance (RDA) of the vitamin.
RDA guidelines for vitamin B12 have been given by the Institute of Medicine (IOM, now National Academy of Medicine) (1), British Nutritional Foundation/National Health Service (BNF/NHS) (2), and the European Union (3). The World Health Organisation (WHO) alongside the Food and Agriculture Organisation (FAO) have also published corresponding values to those given by the IOM (4).
Table: RDA of Vitamin B12 According to the IOM, BNF/NHS, EU and WHO/FAO
Children 1-3 years
Children 4-8 years
Children 9-13 years
Children 14-18 years
Vitamin B12 Daily Requirement for Pregnancy and Lactation
The body’s need for vitamin B12 is greater during pregnancy and breastfeeding. According to the IOM and WHO, pregnant women require roughly an extra 0.2 µg of vitamin B12 in order to cover the requirement of the foetus – giving them a total daily requirement of up to 2.6 µg.
The vitamin B12 concentration in the placenta and the blood of new-borns is around double that of the concentration in the serum of the mother, and furthermore this B12 has to be delivered through the body and nutrition of the mother. Vitamin B12 thus plays an important role in the development of the foetus, which is why it is pivotal to obtain an adequate amount during pregnancy. If the mother does not proceed to take the necessary additional vitamin B12, the requirement can be supplied in some cases from the mother’s B12 store – however, relying on this poses an unnecessary risk to the child.
Whilst lactating, women lose a large amount of vitamin B12 through breastmilk, so the vitamin B12 requirement is even higher at this point than during pregnancy. The IOM/WHO recommends a minimum dose of 2.8 µg for breastfeeding women – so an extra 0.4 µg on top of the daily requirement for adults. Breastmilk contains as much vitamin B12 as the mother’s blood – so it is especially important for vegetarians and vegans to take supplements during this time, as they are at a much higher risk of deficiency whilst breastfeeding, posing a serious risk for the mother as well as the child (5).
Further information: Vitamin B12 During Pregnancy and Lactation
RDA of Vitamin B12 – What is the RDA?
The Recommended Dietary Allowance (RDA) is in fact not the body’s daily requirement exactly, but rather the amount of vitamin B12 which – according to the recommendations of the corresponding organisations – should suffice to cover the minimum daily requirement of 97.5% of healthy people. The RDA is therefore the amount that is required to prevent the onset of clear vitamin B12 deficiency symptoms. The recommendation does already include a safety buffer to account for differing metabolisms (6).
However, these recommendations do not take into account the fact that an absence of deficiency symptoms is not synonymous with an optimal supply. Today, it is assumed that a suboptimal supply of nutrients leads to long-term damage that is not immediately apparent. An optimal supply of vitamin B12 is therefore probably above these given values.
It is also important to be aware that RDAs are only intended to cover the nutritional requirements of healthy people. They do not take into account the increased need for vitamin B12 during times of stress, illness or poor diet, as well as for smokers, drinkers, those taking medication and people with gastrointestinal problems. Moreover, there are further problems with the current recommendations, which we will address below.
Therefore, RDAs should not be treated as the exact daily dose required, but as a benchmark for the minimum requirement, which in ideal situations can be enough to prevent a deficiency. In many individual cases, the actual daily requirement for vitamin B12 is considerably higher.
How is the RDA Calculated?
RDAs are derived from various scientific observations. In the case of vitamin B12, these include:
- The amount of B12 excreted daily
- The size of the body’s B12 store
- Analysis of nutritional studies
- Analysis of studies with anaemia patients and vegetarians/vegans
The reasoning behind the current recommendations is roughly as follows: humans excrete about 1-2 µg vitamin B12 daily from the body’s stores, which contain about 2500 µg vitamin B12 in total.
According to various studies, the body seems to need only about 0.5 – 1 µg vitamin B12 per day for optimal function. Even so, it is worth noting that these values have been derived mainly from studies that were carried out with injections – therefore bypassing the critical phase of vitamin B12 absorption in the intestine (7). However, even if only these 0.5 – 1 µg per injection were absorbed, the body stores would still be emptied over many years due to the slightly higher loss. For this reason, the daily requirement was set between 1 and 3 µg in order to ensure that, in addition to the quantity required for direct health maintenance, an excess is also absorbed which keeps the body’s store full. In this way, the stores can balance the demand at times of low intake, which is particularly crucial in old age.
It is important to add that only 1.5 µg of vitamin B12 can be absorbed per meal/dose via Intrinsic Factor (IF) – the transport molecule that enables B12 absorption in the gut. On looking at the vitamin B12 concentration in food, it is easy to see that hardly more than 4 to 7 µg vitamin B12 per day can be obtained via IF – this correspond quite well to the calculated daily requirement in humans.
Vitamin B12 Daily Requirement: Absorption vs Intake
There are some problems regarding the current RDAs. Firstly, the studies on which the figures are based are old and date from a time before newer methods for determining vitamin B12 deficiency existed.
Plus, intake does not actually equal absorption; a fact that is often overlooked. The vitamin B12 content in the diet and the actual amount of B12 that is absorbed by the body are two completely different things.
Unfortunately, the term ‘intake’ is often used vaguely in this context. It is also odd that RDA values were determined with injections, since it is the B12 absorption that takes place in the intestine that is critical for the body’s overall supply.
The current recommendations assume that general, daily vitamin B12 requirements can be calculated from excretion rates, as well as from studies that have administered injections. This would require, however, that the amount of vitamin B12 supplied is 100% absorbed in the intestine, which is definitely not always the case. Recent studies have shown that the actual requirement is significantly higher: the relevant bio-markers only recover with a dietary intake of 4-10 µg vitamin B12 per day.
Furthermore, in the case of malabsorption about 600 µg vitamin B12 are required to normalise blood levels.
Meeting the RDA
In reality there is a discrepancy between the requirement of the body and the required supply, which can be explained by the way in which the body absorbs vitamin B12. This absorption takes place via two different biological pathways:
- Active intake
via intrinsic factor (IF) – 1.5 µg per meal/dose max., independent of the quantity supplied
- Passive absorption
via passive diffusion – 1% of the quantity supplied
The mechanism of intake through IF recovers over the course of several hours, so that through this pathway 1.5 µg can be absorbed several times a day. A maximum of about 10 µg per day can be obtained this way.
If the potential absorption via IF decreases, which can be the case in old age in particular, only very small amounts of B12 are absorbed through this pathway. To cover the current RDAs, an intake of around 300 µg would be necessary. And even then, this requires healthy intestinal flora.
This explains why many oral vitamin B12 supplements contain very high dosages of vitamin B12: most are designed to cover the RDA via passive diffusion.
Covering the RDA through the Diet
Even with intact IF and a dietary intake distributed over several meals per day, all current studies show that the daily intake must be at least 7 µg to meet the demand:
Table: Vitamin B12 Daily Requirement via the Diet
Bor et al, 2010 (8)
Vogiatzoglou et al, 2009 (9)
Bor et al, 2006 (10)
Kwan et al, 2002 (11)
Tucker et al, 2000 (12)
Hordaland Homocysteine Study (Norwegian)
Framingham offspring (UK)
Recommended supply (μg vitamin B12/day)
These current studies clearly support the argument that the required amount of vitamin B12 is significantly higher than the current recommendations – i.e. an average of about 7 µg spread over the day. It can be assumed that these new findings will be taken into account when the RDA is next revised.
RDA and Vitamin B12 Dosages
In order to reliably cover the vitamin B12 demand through supplements, it is sensible to select a dosage which covers the daily requirement through passive absorption alone. Here is a list of various dosages and the actual intake they achieve:
Table: Calculated Dosage Requirements
|Requirement group||Dose |
|Intake through passive diffusion |
Intake via IF µg
|Healthy adults and teenagers||300||3||1.5||4.5|
|Stress, intense sport||500||5||1.5||6.5|
|People with illness/disease||1000||10||1.5||11.5|
|Children 7 – 13 years||250||2,5||1.5||4|
|Children < 7 years||150||1,5||1.5||3|
In our opinion, there are two main dosages that will cover the daily requirement:
- 500 µg
for all healthy adults with normal requirement and without deficiency symptoms or illness
- 1000 µg
for all people with an increased requirement: pregnant/breastfeeding women, those with symptoms of deficiency, illnesses or the likelihood of absorption disorders
Calculating Your Daily Requirement
So, how can you actually work out your own daily requirement? The RDA values provide a good orientation and should be considered as the intake minimum. However, the values of the current studies around 7 µg are much more reliable. A further increase in demand may be needed in the following cases:
- Stress (physical, mental or emotional)
- Heavy physical exertion (including sport)
- Tobacco, alcohol and coffee consumption
- Consumption of junk food and soft drinks
- Regular intake of medicine
- Disorders of the gastrointestinal mucosa
- Long periods of malnutrition
How much more vitamin B12 is needed in these cases cannot be determined with certainty. As a rough guideline, a requirement can be calculated that is 2-3 µg higher/double the values given in the above-cited studies.
Is it Possible to Cover the B12 Requirement with Food?
Do you obtain enough vitamin B12 in your diet? When is it useful to take supplements?
Vitamin B12 is found only in animal products such as meat, fish, eggs, milk and milk products. Our body best absorbs the vitamin from dairy products and fish; less from meat. An overview of the different quantities of B12 found in various food products can be found in our article, Vitamin B12 Foods.
With an intact IF, no increased need and good health, a balanced omnivorous diet should ensure a good supply of vitamin B12. Also for vegetarians who eat lots of cheese and other milk products the same applies – only slightly reduced. With a vegan diet, however, it is almost impossible to cover the daily requirement without supplements.
Even with an omnivorous diet, a supply is not always assured. Irritations in the intestines, alcohol, coffee and cigarettes, interactions with medicines and many other factors have a very negative effect on B12 absorption. Unfortunately, many of these factors are very common in industrialised countries. The simplest recommendation is to maintain a healthy lifestyle and to avoid these limitations. In case of doubt, the (temporary) use of supplements is recommended in order to prevent larger health risks.
In old age the intake via IF decreases considerably, which is why the intake of supplements is often sensible and sometimes even urgently necessary here.
Vitamin B12 and Vegetarian/Vegan Diets
Since vitamin B12 only occurs in animal foods, it is hard for vegetarians and extremely difficult for vegans to cover their daily requirement through the diet. Especially for vegans, the intake of B12 supplements and/or fortified foods is strongly recommended – this is also recommended by all major vegan associations such as the International Vegan Society.
More information can be found in our article: Vitamin B12 for Vegetarians and Vegans
Daily Requirement, Dosage and Overdose
Vitamin B12 is water-soluble and that which is not required by the body is simply excreted in the urine. The vitamin is considered harmless and thus no maximum intake limit has been defined. A vitamin B12 overdose has never been recorded.
The long-term consequences of taking quite high doses of 2000 µg of B12 per day have been shown to be problem-free for anaemic patients – even when taken for many years. One should nevertheless bear in mind that the human metabolism is a sensitive equilibrium, and an unnecessary overdose of vitamins certainly creates a burden in any case for the kidneys, via which vitamin B12 is excreted.
Details on the correct dosage of vitamin B12 supplements can be found in our main article, Vitamin B12 Dosages.
- 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
- British Nutritional Foundation, Nutritional Requirements, “Reference Nutrient Intakes for Vitamins”, UK 2016, https://www.nutrition.org.uk/attachments/article/234/Nutrition%20Requirements_Revised%20Oct%202016.pdf
- Richtlinie 2008/100/EG der Kommission vom 28. Oktober 2008 zur Änderung der Richtlinie 90/496/EWG des Rates über die Nährwertkennzeichnung von Lebensmitteln hinsichtlich der empfohlenen Tagesdosen, der Umrechungsfaktoren für den Energiewert und der Definitionen http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:285:0009:01:DE:HTML
- Subcommittee on the Tenth Edition of the RDAs, Food and Nutrition Board, Commission on Life Sciences, National Research Council: Recommended Dietary Allowances: 10th Edition. National Academy Press, Washington, D.C., 1989 http://www.nap.edu/catalog.php?record_id=1349
- World Health Organization, Food and Agricultural Organization of the United Nations „Vitamin and mineral requirements in human nutrition“, Second edition, WHO, 2005.
- Specker, B.L., D. Miller, E.J. Norman, H. Greene, and K.C. Hayes. 1988. Increased urinary methylmalonic acid excretion in breast-fed infants of vegetarian mothers and identification of an acceptable dietary source of vitamin B12. Am. J. Clin. Nutr. 47:89-92.
- Herbert, V. „Nutritional requirements for vitamin B12 and folic acid“ Am. J. Clin. Nutr. 21:743-752, 1968.
- 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.
- Vogiatzoglou A, Smith AD, Nurk E et al. Dietary sources of vitamin B-12 and their association with plasma vitamin B-12 concentrations in the general population: the Hordaland Homocysteine Study. Am J Clin Nutr 2009;89:1078–87.
- Bor MV, Lydeking-Olsen E, Møller J, Nexø E . A daily intake of approximately 6 micrograms vitamin B-12 appears to saturate all the vitamin B-12-related variables in Danish postmenopausal women. Am J Clin Nutr 2006;83:52–8.
- Kwan LL, Bermudez OI, Tucker KL. Low vitamin B-12 intake and status are more prevalent in Hispanic older adults of Caribbean origin than in neighborhood-matched non-Hispanic whites. J Nutr 2002;132:2059–64.
- Tucker KL, Rich S, Rosenberg I, et al . Plasma vitamin B-12 concentrations relate to intake source in the Framingham Offspring study. Am J Clin Nutr 2000;71:514–22.
- Eussen SJ, de Groot LC, Clarke R, Schneede J, Ueland PM, Hoefnagels WH, van Staveren WA. Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch Intern Med. 2005 May 23;165(10):1167-72.