Trying to stay healthy can seem like a full-time job sometimes, especially with all the conflicting

information that's out there.

But I'm here to make that job a little easier.

Welcome to the Nutrition Facts podcast.

I'm your host, Dr. Michael Greger.

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

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 1 microgram of B12 a day,

and the bioavailability of tiny amounts of B12 from food is assumed to be about 50 percent,

if you've got two micrograms a day, you'd absorb 1 microgram, 50 percent,

and that would replace the 1 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 percent of the population,

which just means you up the average requirement by 20 or 40 percent.

So if we add 20 percent to that two micrograms a day we came up with, that comes out to

2.4, which is indeed exactly 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.

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