How Much Vitamin B12 Do We Need Each Day?

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How are the recommended daily and weekly doses of vitamin B12 derived?

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

There are a couple ways to derive vitamin B12 recommendations. One is called the factorial approach, in which the average requirement of vitamin B12 is calculated as a replacement of daily losses, adjusted for dietary bioavailability. So, for example, if people lose an average of one microgram of B12 a day, and the bioavailability of tiny amounts of B12 from food is assumed to be about 50%, if you got two micrograms a day, you’d absorb one microgram—50%—and that would replace the one microgram you lose every day. But that’s just the average daily requirement, based on average daily losses. The average requirement would mean 50% of people actually need less, and 50% need more. You don’t want to cover the needs of only half the population though, so you add two relative standard deviations to cover more like 98% of the population, which just means you up the average requirement by 20 or 40%. So, if we add 20% to that two micrograms a day we came up with, that comes out to 2.4, which is, indeed, the RDA for B12 in the United States. And other countries are similar, recommending 1.5 to 4 micrograms a day.

Another way to derive B12 recommendations is to see what dose maximizes B12 function within the body. B12 is used to metabolize methylmalonic acid (MMA) and homocysteine, and it looks like there’s additional benefit up to an intake of six micrograms. So instead of an RDA of 2.4, maybe we should tell people to get six micrograms, since that appears to normalize all the vitamin B12–related variables. A subsequent, larger study using the same principle found the same kinds of curves, maximizing B12 functionality in the same range, suggesting again, instead of 2.4, maybe we should tell people to get somewhere between four and seven. Since the bioavailability of tiny amounts in the diet is assumed to be around 50 percent, that would mean we should shoot for absorbing two to 3.5 micrograms into our body every day.

The bioavailability of larger amounts found in supplements is different though, based on the famous Heinrich equation. Down at one or two micrograms, B12 absorption is about 50%. But as you can see, only about 1% of a 2,000-microgram dose is absorbed. Okay, so if we want to absorb two to 3.5 a day through fortified foods or supplements, what do we do? Well, if we ate B12-fortified foods at every meal, three times a day, how much would we have to get at each meal? If each meal had two micrograms, then we would absorb throughout the day 0.9 times three, or 2.7, which would be in the two to 3.5 range we’re shooting for.

So, if you had even like three-quarters of a cup (180 ml) of soymilk at breakfast, and then sprinkled on as little as one teaspoon of certain brands of nutritional yeast on your lunch and dinner, you’d be all set.

Instead, if you were going to take supplements, how much would you have to take each week to absorb two to 3.5 micrograms worth a day? Well, if you took 2,000 once a week, that would get you 19.5, which would average out to about 2.8 a day. If you’d rather take a supplement once a day instead of once a week, 50 microgram tablets are most frequently advised and used. In theory, 50 microgram would get you 1.9, and in practice, it looks like 50 does get you that two micrograms. And, indeed, in a comparison of chewable 50 microgram daily doses to 2,000 once-a-week doses in vegans and vegetarians with marginal deficiency, they both worked just as well in bringing down MMA and homocysteine levels.

One option for fortified foods that have enough for once-a-day dosing is LeafSide, just-add-water whole food, plant-based meals that have 75 micrograms of B12 per serving. Please note that neither I nor NutritionFacts.org have ever and will ever accept any money to promote any for-profit product. So, unlike almost anywhere on the internet, you know that when I plug a product, it’s strictly because I believe in it and think it’s going to help people, not because it’s lining my pockets.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

There are a couple ways to derive vitamin B12 recommendations. One is called the factorial approach, in which the average requirement of vitamin B12 is calculated as a replacement of daily losses, adjusted for dietary bioavailability. So, for example, if people lose an average of one microgram of B12 a day, and the bioavailability of tiny amounts of B12 from food is assumed to be about 50%, if you got two micrograms a day, you’d absorb one microgram—50%—and that would replace the one microgram you lose every day. But that’s just the average daily requirement, based on average daily losses. The average requirement would mean 50% of people actually need less, and 50% need more. You don’t want to cover the needs of only half the population though, so you add two relative standard deviations to cover more like 98% of the population, which just means you up the average requirement by 20 or 40%. So, if we add 20% to that two micrograms a day we came up with, that comes out to 2.4, which is, indeed, the RDA for B12 in the United States. And other countries are similar, recommending 1.5 to 4 micrograms a day.

Another way to derive B12 recommendations is to see what dose maximizes B12 function within the body. B12 is used to metabolize methylmalonic acid (MMA) and homocysteine, and it looks like there’s additional benefit up to an intake of six micrograms. So instead of an RDA of 2.4, maybe we should tell people to get six micrograms, since that appears to normalize all the vitamin B12–related variables. A subsequent, larger study using the same principle found the same kinds of curves, maximizing B12 functionality in the same range, suggesting again, instead of 2.4, maybe we should tell people to get somewhere between four and seven. Since the bioavailability of tiny amounts in the diet is assumed to be around 50 percent, that would mean we should shoot for absorbing two to 3.5 micrograms into our body every day.

The bioavailability of larger amounts found in supplements is different though, based on the famous Heinrich equation. Down at one or two micrograms, B12 absorption is about 50%. But as you can see, only about 1% of a 2,000-microgram dose is absorbed. Okay, so if we want to absorb two to 3.5 a day through fortified foods or supplements, what do we do? Well, if we ate B12-fortified foods at every meal, three times a day, how much would we have to get at each meal? If each meal had two micrograms, then we would absorb throughout the day 0.9 times three, or 2.7, which would be in the two to 3.5 range we’re shooting for.

So, if you had even like three-quarters of a cup (180 ml) of soymilk at breakfast, and then sprinkled on as little as one teaspoon of certain brands of nutritional yeast on your lunch and dinner, you’d be all set.

Instead, if you were going to take supplements, how much would you have to take each week to absorb two to 3.5 micrograms worth a day? Well, if you took 2,000 once a week, that would get you 19.5, which would average out to about 2.8 a day. If you’d rather take a supplement once a day instead of once a week, 50 microgram tablets are most frequently advised and used. In theory, 50 microgram would get you 1.9, and in practice, it looks like 50 does get you that two micrograms. And, indeed, in a comparison of chewable 50 microgram daily doses to 2,000 once-a-week doses in vegans and vegetarians with marginal deficiency, they both worked just as well in bringing down MMA and homocysteine levels.

One option for fortified foods that have enough for once-a-day dosing is LeafSide, just-add-water whole food, plant-based meals that have 75 micrograms of B12 per serving. Please note that neither I nor NutritionFacts.org have ever and will ever accept any money to promote any for-profit product. So, unlike almost anywhere on the internet, you know that when I plug a product, it’s strictly because I believe in it and think it’s going to help people, not because it’s lining my pockets.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Doctor's Note

This is the fourth video in a five-part series on vitamin B12. If you missed any of the previous ones, check out:

Stay tuned for Are Large Weekly Doses of Vitamin B12 Safe?.

For more on vitamin B12, check out the topic page.

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