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 percent, if you've got two micrograms a day,

you'd absorb one microgram, 50 percent, 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 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.

B12 is used to metabolize MMA and homocysteine, and 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, 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

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