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I read some questions in this site regarding B12. Some said 50 mcg was required per day, while some said 1000 mcg.

While Vegan Society says 3 mcg per day atleast.

What is the amount of B12 required per day to have a healthy body?

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    While not a complete duplicate, I think your question can be pretty much covered by the answer to this one. Feel free to leave this one here though since I don't think we have this one covered here so far. – Alexander Rossa Mar 17 '18 at 21:07
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For vitamin B12 oral intake, 1,000 mcg daily is both safe and sufficient.

Update: A recent randomized controlled trial of vegetarians and vegans who were marginally B12 deficient showed that 50 mcg B12 taken daily was sufficient to correct B12 status. Effect of two different sublingual dosages of vitamin B12 on cobalamin nutritional status in vegans and vegetarians with a marginal deficiency: A randomized controlled trial

Absorption Pathways

Guidelines from NIH suggest that we need 0.4 - 2.8 mcg B12 depending on our stage of life. The large difference between requirement and recommended supplemental intake arises from the different ways that vitamin B12 is absorbed in the body.

  • Intrinsic factor in our stomach helps us to absorb about 2.0 mcg of B12 per meal. However, some people have pernicious anaemia, a condition in which they cannot make intrinsic factor and therefore have trouble absorbing B12 this way. This is more common in elderly individuals with impaired intestinal absorption.
  • Passive diffusion allows about 1.2% of dietary B12 to enter the bloodstream, even in the absence of intrinsic factor. So in a tablet containing 1000 mcg, up to 12 mcg may be absorbed which is sufficient to meet the recommended daily amount.

Safety

No harmful effects have ever been shown from consuming too much vitamin B12, and no maximum dose has been identified. Vitamin B12 is water-soluble and excess vitamin will be rapidly excreted in the urine over the course of a few days.

However, take care with multivitamins and b-complex vitamins because vitamin B6 has a tolerable upper limit of 100 mg/day in adults, and excess B6 can be harmful.

See also: Can too much B12 be harmful?

Food sources of vitamin B12

Vitamin B12 in chicken eggs is poorly absorbed compared to other animal sources, so ovo-vegetarians are also advised to take B12 supplements.

Supplemental sources of vitamin B12

Oral doses of vitamin B12 of at least 1000 mcg are considered just as effective as intramuscular injection.

Vitamin B12 status among Canadians

A 2011 study of 5600 Canadians showed that about 4.6% of the population had low vitamin B12 status (<148 pmol/L in the blood).

Among Canadians, typical B12 concentration in the blood is 350 pmol/L when not taking supplements. On supplements, B12 concentration may rise to 550 pmol/L or higher.

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I am a vegetarian for about 6 years and my experience has been that if i do get my blood checked once a year, for B12, I then decide if and how much B12 to supplement. There are many different body types and everybody works differently. But when you stay checked you do get a pretty good feeling about your own body, which is the most important and where you want to be, healthy and strong.

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    Welcome to Vegetarisnism SE :). While you definitely gave a good recommendation, the OP specifically asked about the required amounts of B12. While there is some disparity in the recommendations (see OP's question) you could perhaps mention what benchmark you use for deciding how much B12 to supplement and why you use this benchmark. – Alexander Rossa Mar 21 '18 at 16:17
  • I think this addresses the question: everyone’s requirements will differ and this is best decided in consultation with a medical professional (with regular tests). – Tom Kelly Mar 23 '18 at 7:41
  • Bear in mind vegans (to whom this issue is especially pertinent) also use this site and their requirements may differ. – Tom Kelly Mar 23 '18 at 7:44
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You need far less daily than most supplement regimes provide. However, this is deliberate: there is an issue with bioavailability and absorption. Still in most cases, medical professionals will advise supplementation of no more than standard over-the-counter supplements 25-50µg once per day. Note than this is "micrograms" (a.k.a. mcg) and milligrams (mg) is far in excess of what most people need.

Usually supplementation is only needed for vegans (or vegetarians with low egg and dairy intake). There is no immediate risks of overdose but many health food companies will market products with far higher doses than necessary. Unless you absolutely need these, it is not worth the additional expense which adds up over the course of a daily medication. If you have particular deficiency concerns, you may need injection or other treatment to ensure absorption. Vitamin B12 can be accumulated and stored in the body. If you are experiencing extreme deficiency, presenting symptoms, or at risk of chronic illness, you may be put on a course of higher dose supplementation to restore these stored vitamin reserves.

This is a serious health concern so if you have any concerns about B12, consult a medical professional. Any GP can order blood tests and monitor your vitamin levels. There are many ways to manage vitamin deficiency to varying degrees of severity and how your specific case develops over time so this matter is best discussed with a qualified doctor.

  • Vitamin B12 is water-soluble, not fat-soluble. – Nic Mar 21 '18 at 23:52
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    Indeed it appears that it is. My minor mistake, it does not affect my heath recommendations. Next time, you are welcome to submit an edit request to address such minor inaccuracies. – Tom Kelly Mar 23 '18 at 7:39

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