How much b12 should be taken in a day?

[JhonnyBoy]

I got to know from a member of this forum named fbrider that the body can only absorb a limited amount of b12 at a time and it is useless to take enormous doses at once.I would like to know what does 'at a time' mean?What i mean to say is that what is the minimum time after the first supplement is taken after which a second supplement of b12 can be taken so that it is absorbed separately from the first supplement.

[Gambit62 Administrator]

the amount of B12 that can be absorbed in the ileum is limited

ncbi.nlm.nih.gov/pmc/articl...

Extracts:

....Absorption of Cbl from supplements depends on the dose and frequency of the intake [170]. The absorption capacity depends on the saturable active transport and on the efficiency of the aspecific route. The consumption of oral doses of 1 μg, 10 μg, 50 μg, 500 μg, 1000 μg, are absorbed with an efficiency of 56%, 16%, 3%, 2%, 1.3%, respectively [151].

According to Carmel, a single oral dose of 50 μg, 500 μg or 1000 μg will be absorbed at an amount of 1.5 μg, 9.7 μg or 13 μg, respectively [151].

The figures above are averages.

The limitation is the amount that can be absorbed in a single meal ... so a little often would seem to be more efficient.

The article also says that presence of other vitamins and minerals - specifically mentions vitamin C and copper - may make use of multivitamins inefficient.

[Meblue in reply to Gambit62]

What percentage is absorbed from higher than 1000 like 5000?

[Gambit62 Administrator in reply to Meblue]

Meblue, nobody has done any experiments to find out but it's going to be around 1%

[TACCT in reply to Meblue]

Given the pattern above, it may be less than 1% but we do not have any evidence for it. I have found some studies which mentioned 1000mcg a day to treat b12 deficiency.

[helvella in reply to Gambit62]

The limitation is the amount that can be absorbed in a single meal ...

I'm not sure whether we absorb better when taking supplemental forms well away from food? Or with food?

[Gambit62 Administrator in reply to helvella]

some are absorbed better with food - some are absorbed better away from food.

I can't point to any studies but the need for stomach acidity etc in order for B12 to be absorbed would suggest to me that it probably is best absorbed as part of a meal.

[fbirder in reply to Gambit62]

Stomach acid is required to liberate B12 attached to proteins in food. Supplemental B12 isn't attached to food proteins and doesn't need stomach acid. Once the stomach acid releases the B12 it binds with haptocorrin (HC) produced in the saliva. This protects the B12 molecule from attack by the stomach acid.

Once the HC-B12 passes into the duodenum, proteases from the pancreas split the complex, allowing the free B12 to bind with IF that was secreted in the stomach (if you don't have PA). The IF-B12 passes on to the ileum.

In the ileum the IF is grabbed by transporter cells that carry it across the gut wall, taking the B12 with it. The rate at which it gets transported will depend on several factors. The two main ones are - the frequency with which IF-B12 encounters a transporter, and the capacity of the transporter.

Not all of the IF-B12 will encounter a transporter cell. The smaller the amount of B12, the smaller the amount that can be transported. As the amount of B12 in that portion of the gut increases, the more IF- B12 will encounter a transporter and the more will be absorbed.

But the transportation mechanism doesn't have infinite capacity. As the amount of IF-B12 increases, the closer it gets to capacity and the smaller the fraction that gets absorbed.

Imagine you're a sorter in a biscuit factory. Your job is to remove the oddly shaped biscuits as they pass you on a conveyor. If there are just a few odd-shaped biscuits then you'll get most of them, but the total amount will be small. As the number of odd-shaped biscuits increases you'll catch more in total, but the fraction that you miss will increase.

Until you get to the point that you are pulling funny biscuits off the conveyor as fast as you possibly can - you have reached your capacity. As the number of odd-shaped biscuits increases you cannot remove any more. The total amount removed stays the same, but the fraction removed decreases.

[deniseinmilden]

Everyone is different and while the science that is out there is OK, it is only part of the picture and there is a lot of research still to be done - lots of people report findings that don't fit within the scope of the current knowledge. Because B12 is so safe it is worth experimenting to see what suits you.

What suits one person may not work for another.

Different amounts can be absorbed through the digestive tract depending on what condition affects you and how severely you are currently affected, as well as your basic make-up, weight, age, etc. Just because you could absorb "x" amount 10 years ago doesn't mean you can rely on absorbing this much forever. Unfortunately!!!

A similar principle applies to absorption through the mouth, nose, skin, etc.

And then, once it has got into our blood, how it's is stored and processed by our bodies - or not - AND the uptake from the blood into our cells also varies hugely between people!

That is how some people are fit and well on a low-B12 intake, vegetarian diet and some people need to inject 3mg every day just to keep going!

That is why the NHS "1mg injection every 3 months" protocol is fine for the mathematically determined "average" person but doesn't actually work for hardly anyone in practice!

We have to be much more careful with the amounts we take of other vitamins and minerals as they do not have anywhere near such a wide safety margin: the amount in your body of one thing can have a significant impact on the effective operation of something else and can have a damaging effect if present in excess. But even with these, the way our individual bodies work and the output we expect if them, determins how much each individual person needs of each vitamin and mineral.

The guideline amounts are for people who are functioning properly and therefore feel well. The medical/veterinary/agronomy skill comes in when we have symptoms, in determining what is preventing things from working properly and what adjustments are needed to restore the balance and hence reduce the symptoms.