Some supplement amounts massively exceed NRV?

I’ve noticed that quite a lot of supplements available massively exceed the NRV for that item. For example, the NRV for vitamin B12 is 2.5µg yet here is a link to a supplement which contains 500µg, 20,000% of the NRV. Further still on the website it says “take 1 or 2 tablets daily” meaning you could be getting 40,000% of NRV.

This is the most extreme case I have found but I have found plenty of others which exceed NRV by hundreds or thousands of a percent.

Am I missing something here? As these are to supplement the food already being consumed, why are some of the values so high?

Having recently switched it up to vegan, I found myself confused by the same thing.

With regards to B12, here’s an answer from Dr Michael Greger’s excellent YouTube channel


I’m OK with that video up to the point where he says “so we should take at least 2500μg a day”. He’s just worked out we need 4μg per day to achieve his sums and then says that?

He says 2500μg once per week, not per day.

In short, the NRVs are enough to avoid deficiencies (for 97.5% of the population), but there can be benefits from above NRV consumption of certain micronutrients.

When it comes to B12 specifically though, I do question the use of 500 micrograms all at once, simply due to the method through which it is absorbed.

According to here, “The absorption of vitamin B12 mediated by intrinsic factor is limited to 1.5-2.0 µg per meal because of the limited capacity of the receptors. In addition, between 1 percent and 3 percent of any particular oral administration of vitamin B12 is absorbed by passive diffusion. Thus, if 1000 µg vitamin B12 (sometimes used to treat those with PA) is taken orally, the amount absorbed would be 2.0 µg by active absorption plus about 30 µg by passive diffusion.”

So with an individual 500 microgram tablet, you’d absorb 2.0 micrograms via active absorption and 5-15 micrograms passively, for an overall absorption of 7-17 micrograms - still decently above the NRV, but not by as ridiculous a percentage as the label suggests. Given the poor rate of B12 absorption from food, and the subsequent rate of deficiencies that need to be corrected, it does actually end out as quite an appropriate dose.


Sorry, I meant to say once per week.

  1. Per meal, your body limits the amount of B12 you can absorb to 1.5 - 2 µg;
  2. 1% of the remainder of whatever dose you’ve taken goes into the blood stream to be absorbed later (2500µg becomes 25µg in the blood, 3000µg becomes 30µg, and so on);
  3. The 25µg in your blood plus the 2µg already absorbed equals 27µg;
  4. 27µg over 7 days equals an average of 3.85µg. Even if diminished amounts are available for absorption over the last couple of days, it doesn’t matter because the body is (according to Dr Greger) very good at holding onto the B12 it has absorbed.

Sorry, I have butchered my attempts at trying to get my question across. What I mean is you can get much smaller B12 supplements than 2500µg. I’ve seen them as low as 100µg per capsule. Surely this dose once a week would still be enough to achieve the goals and is significantly less than 2500µg? I know the article is saying the excess comes out in the form of a number 1 but I’d rather not be putting in enormous amounts of something just for it to be filtered and come out again when there are smaller doses available.

100 micrograms a week may well be insufficient due to how it’s absorbed. Assuming you take that 100 micrograms all at once, 2 micrograms will be absorbed actively, and 1-3% will be absorbed passively. Taking the upper end of that scale with 3%, that gives an extra 3 micrograms, for a total absorption of 5 micrograms. With the NRV being 2.5 micrograms, that’s only enough for two days.

The optimal strategy for maximising B12 intake is to split up intake throughout the day wherever possible to maximise the amount you get through active absorption. If you’re going the 1/day or 1/week route, you need to largely take advantage of passive absorption, in order to supply the extra 0.5 micrograms (for 1/day) and 15.5 micrograms (for 1/week) - those amounts having been calculated by taking the 2 micrograms from active absorption away from the NRV for 1 and 7 days respectively.

So you need to absorb 0.5 micrograms passively for 1/day supplements and 15.5 micrograms for 1/week supplements.

As passive absorption is only 1-3%, that means you’d need at 16.6666-50 micrograms in the supplement to get the 0.5 micrograms of passively absorbed B12 for 1/day (so a total supplemental intake of 18.666666-52 micrograms for a 1/day supplement).

For the 1/week supplement, to get the 15.5 micrograms through passive absorption, you need 516.666666-1550 micrograms, or a total supplemental intake of 518.666666-1552 micrograms to ensure 17.5 micrograms absorbed in total (enough to cover 7 days of the 2.5 microgram NRV).

So yeah, in short the supplements with the highest intake like the one you pointed out should either be recommending only weekly supplementation or else are designed to correct deficiencies somewhat (or they’re just trying to make money). In terms of what you should look for if aiming for a 1/day or 1/week supplement, I’d aim for a 50 microgram and a 1500 microgram supplement respectively based on the numbers, though for something like B12 that doesn’t have an upper limit, more wouldn’t hurt.

This reminds me of a TED talk by a doctor who got sick (MS) and studied nutrition to try and cure it. She found out from nutritionists and literature that the optimum levels of vitamins and minerals for mitochondria to perform well are quite a bit higher than suggested intakes, and far higher than what the average westerner consumes. I think aside from the generally enjoying eating, that this puts me off a 100% Huel diet, although some of the vits & mins are accounted for and have over the 100%.
Her ‘health diet’ gives the amounts needed to supposedly reverse progressive MS (many success stories but diets are notoriously hard to test clinically- too many other factors), which involves a lot of food- mostly vegetables- along with some high quality proteins and little or no grains. I forget exactly which vits & mins she emphasises though.

Ooh this is interesting. In the products I sell I’ve tried to take account of more optimal intake levels, but her research could greatly help with this aim. Do you happen to have a link to the TED talk (or remember her name) by any chance?

I had to search for it, here’s the link to the talk
It may be hard to find her suggested intakes without giving her money though, the talk was flagged because it’s basically an advert for her books and resources- so take with a pinch of salt. And upon re-watching it, I think the emphasis on suggested intake vs optimal intakes was in a different article about her work, but she does give a run down on the quantities of which food types per day. I think she’s finally managed to get clinical trials started now.