This is vital information so let’s take heed.
In the US, a deficiency in vitamin B12 is generally considered to be blood concentrations below 150 pmol/L. The consensus cutoff for deficiency in Japan is much lower at 200 pg/mL – this is based on the average intake of vitamin B I was able to find an old study from 1997 which found that up to 21% of elderly people were deficient in B12 (I’m not sure if the average intake of Japan has changed since 1997 or not).
In Western countries, we rely almost exclusively on dietary sources (and to a much lesser extent, supplements) for vitamin B12. However, vegan diets are low in vitamin b12 unless fortified with it. It is also important to note that vitamin B12 found in animal products is bound to protein, and this limits its bioavailability.
It has been suggested that it may be up to 80% more effective to take unbound (i.e. not protein-bound) supplemental forms of b12 like methylcobalamin, assuming equivalent intake of total vitamin b12 to that found in animal products.
The RDA for vitamin B12 is 2.4µg, and there is no upper limit set (in contrast to vitamin A or niacin, which indicates toxicity with prolonged intake above the UL).
However, many people get more than enough vitamin B12 from their diets (especially those on a Western diet). Although there is no evidence of B12 deficiency at intakes as high as 1,000 µg/day from food sources alone, it has been suggested that absorption of supplemental vitamin B12 decreases with intake above 500 µg/day.
In other words – although there’s no evidence that you need to lower your intake of vitamin b12 when supplementing, it’s probably a good idea.
Speaking of supplements – because dietary sources are absorbed with intrinsic factors (an acid-labile protein secreted by the stomach) and thus need to be freed from their binding proteins before absorption can occur, supplemental forms are usually in the form of cyanocobalamin or hydroxocobalamin.
Cyanocobalamin is usually derived from bacterial sources, while hydroxocobalamin is typically produced through the conversion of cyanocobalamin.
Cyano and hydroxo are not easily distinguished in most tests since they both have cobalt at the center of the molecule – thus most tests will report “vitamin B12” regardless of the actual compound.
There are two proteins that enable absorption of B12 (intrinsic factor and haptocorrin), but the only intrinsic factor is needed for vitamin b12 to be absorbed into the body.
Haptocorrin binds tightly to the vitamin, so it isn’t available for absorption. If you have a deficiency in vitamin b12, your body will decrease the production of haptocorrin.
The cells lining the stomach produce intrinsic factors. In the presence of pepsin and hydrochloric acid from the stomach, B12 is freed from dietary protein by pepsin cleavage of the R-group. After that, B12 can bind to intrinsic factors, and be absorbed by receptor-mediated endocytosis.
Intrinsic factor itself is a protein secreted by the parietal cells of the stomach mucosa. It binds to vitamin B12 once that has been freed from dietary protein by pepsin cleavage of the R-group, allowing the B12-intrinsic factor complex to bind to the ileal receptor.
If you don’t have enough intrinsic factors or if your ileum is damaged, you won’t be able to absorb vitamin b12 properly.
This is because haptocorrin and intrinsic factor work together: haptocorrin binds to free B12, which is then picked up by intrinsic factor. As haptocorrin levels decrease, there will be enough vitamin b12 for the body even if you don’t have adequate intrinsic factors.
However, as I mentioned above – this does not necessarily mean that your vitamin b12 intake is low – it simply means that you have a functional system for absorbing it even if your intrinsic factor levels are low.
The RDI of vitamin b12 is 2.4 mcg/day, and as I mentioned above – you can get that from foods rich in B12 or from supplements with appropriate metabolic activation (to free the vitamin from its binding proteins).
One of the best sources of this essential vitamin is via Liver. I know it sounds disgusting but hear me out. Back in the days, when our parents went to the routine check up, the medical staff used to ask, “would you like a B12 shot?” Now when you go, you seldom hear that.
It’s important we become cognizant of our dietary habits because as we age it could have dire consequences. You are what you eat.
Here’s a link to a keto diet I wrote about on medium. You can purchase a keto meal plan from here
Knight Writer
View More PostsI am a young, free-spirited individual who loves to learn every day and challenge myself to become a better version through each passing day. Also, I am here to help people with my writing and knowledge of online money-making and mental health issues. Feel free to leave a comment anytime, and I will respond as soon as I can. Thank you, and stay blessed.
12 thoughts on “Vitamin B12 Deficiency”
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