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I’ve talked about the optimal dose of vitamin B12 supplements for adults, as well as in childhood, pregnancy, and old age to prevent vitamin B12 deficiency. But what if you already have it? How much do you have to take to treat it?

Your doctor might want you to get vitamin B12 injections, but oral B12, even for those who can’t absorb it well, has long been considered one of medicine’s best kept secrets. It is now considered well-known that orally administered B12 supplements are “as effective in overcoming deficiency states as intramuscular” injections when you get up to taking 1,000 micrograms a day. How long do you have to take 1,000 a day for? It depends how low your levels start out.

Because B12 status in pregnancy is so critical, there is a suggestion that plant-based women get it checked throughout pregnancy and to adjust supplementation as necessary. This is how much you should take if you’re low. Note the recommendations for pregnant and breast-feeding women are the same as everyone else over the age of 10. So, if you’re a teen or adult diagnosed with vitamin B12 deficiency, you’d take 1,000 micrograms a day for one to four months, depending on how low you start out, before going back to a regular maintenance dose of 50 a day or 2,000 a week, with toddlers and small children taking smaller doses.

There are two main types on the market, though: methylcobalamin, marketed as methyl B12, and cyanocobalamin, typically marketed as just vitamin B12. Methyl is more expensive so it must be better, right? Wrong. Cyanocobalamin “is the most used form due to its high stability.” See, “methylcobalamin is less stable than cyanocobalamin, and it is particularly susceptible to photodecomposition,” meaning destruction from being exposed to light. “There is no advantage to using the light-sensitive forms of cobalamin, such as methyl B12…, instead of the stable cyano…forms, which are readily converted in the body” into the type you need, where you need it.

The one major exception may be kidney failure, though. Methylcobalamin may be better for those with impaired kidney function. It’s been speculated that oral methylcobalamin or injected hydroxycobalamin may also be preferable in smokers, though it has yet to be confirmed. Because methylcobalamin is less stable, you’d probably want to take much higher doses. So, for example, in those with kidney failure you’d be taking one to two thousand micrograms a day, compared to just 50 micrograms of cyanocobalamin in someone with normal kidney function. Another reason to use the cyanocobalamin as opposed to the more expensive kinds is that it has a track record of safety and efficacy, whereas for example, in one study even up to 2,000 micrograms a day of methylcobalamin wasn’t enough to correct vitamin B12 deficiency in one of three vegans they tested it on.

The bottom line is that so-called coenzyme forms of B12, like methyl B12 and adenyl B12 (also known as adenosyl b12), “are not likely to be superior to cyanocobalamin,” which is more stable. Cyanocobalamin “appears to be best suited for oral supplementation,” which is why I specify its use in my recommendations.

Note I also recommend ideally taking it separately as a chewable, sublingual, or liquid supplement. Why can’t you just get it as part of a multivitamin or something? Because various vitamins and minerals mixed into the same pill can “destroy” active B12, forming B12 analogues, B12-look-alikes that not only can our body not use, but the analogues can be “potentially harmful” because they can inhibit the transport of what little B12 is left. That’s why using multivitamins can even be counterproductive for the supplementation of vitamin B12. And this isn’t just in theory. There was a tragic case of severe vitamin B12 deficiency in an infant born to a vegan mother who thought she was doing everything right taking a multivitamin that contained B12, though it may have also just been inadequate dosing.

Why chewable or sublingual? Absorption is boosted when the B12 mixes with saliva, since you secrete a B12 binding protein from your salivary glands that helps transport B12 safely through the digestive tract. Having people chew a tablet of B12 and their B12 levels go up ten times more than just simply swallowing the exact same pill. Check it out. Vegans boosted out of deficiency chewing a B12 supplement, but nothing in those who just swallowed it whole. Maybe they had some sort of absorption problem or something? No, because then if you tell them to start chewing it instead of swallowing it whole, their levels shoot right up as well.

In my latest book How Not to Diet, I suggest a third option to B12-fortified foods and supplements—brushing twice daily with a B12-fortified toothpaste—specifically this brand, which was put to the test in two double-blinded, randomized, placebo-controlled studies. “Participants were instructed to use the toothpaste two times a day for two minutes at a time,” and indeed, it was able to correct the markers of B12 insufficiency in the blood of vegans and among the elderly, but that was on average. Unfortunately, it didn’t work in every last person, which is why it’s not included in my recommendations. Though, look, if you get your levels tested before and after brushing for a few months and they go up, you could presumably stick with it.

In summary, vitamin B12 deficiency is not to be messed around with, with the potential to cause a wide range of disorders of the gut, blood, brain, and nervous system. “With the ever-increasing demand for cleanliness in our food chain”—which is a very good thing—”it is of special importance that we secure” a regular reliable source, and the safest, cheapest, healthiest source is B12 supplements or green light B12-fortified foods.

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