Food Sources and Absorbability of Active Vitamin B12

Vitamin B12 (cobalamin) is a crucial nutrient for metabolic functioning, and low levels are associated with a vast array of health problems from heart disease and diabetes to depression and dementia, due to the buildup of homocysteine and inability to perform important methylation reactions in the body. The classic results of B12 deficiency are megaloblastic anemia and neuropathy. Vitamin B12 is an essential part of the methionine and folate cycles.

This article will explain which foods contain vitamin B12, the types of B12 in food, which forms are best absorbed and utilized, and some thoughts on choosing a form of B12 to supplement with. It also includes a section about food sources of vitamin B12 for vegans. A separate article here on MindWhale explains food sources of methylfolate.

Food Sources of Vitamin B12

Animal foods are the primary source of cobalamin, with plants containing no appreciable quantity (exceptions noted at the end in the vegan sources section). Most meat (especially unprocessed meat) likely has reliable quantities of vitamin B12.

The top sources of vitamin B12 are (with %DV):

  1. Sardines (338%)
  2. Salmon (236%)
  3. Tuna (111%)
  4. Cod (109%)
  5. Lamb (105%)
  6. Scallops (102%)
  7. Shrimp (78%)
  8. Beef (60%)
  9. Yogurt (38%)
  10. Cow’s milk (23%)
  11. Nori, a type of seaweed (8%)

Types of Vitamin B12 Found Naturally in Food

Prepared animal foods contain varying proportions (in roughly descending order) of 1) hydroxocobalamin, 2) adenosylcobalamin, 3) methylcobalamin, 4) sulphitocobalamin, and 5) cyanocobalamin. Hydroxocobalamin and adenosylcobalamin are the most abundant in foods and are found in roughly equal quantities. However, it should be noted that since light degrades methylcobalamin into hydroxo– and adenosyl-cobalamin, it is possible that much of the methylcobalamin was transformed during the studies, falsely elevating the detected quantities of these and lowering the detected quantity of methylcobalamin. In other words, fresher cuts of meat from healthier animals likely have a higher proportion of active, methylated methylcobalamin. Cheeses and egg yolk seem to have proportionally the most methylcobalamin. Foods have very little B12 in the cyanocobalamin form.

Vitamin B12 Absorption and Utilization

In the body, active folate (methylfolate) directly methylates non-methylated cobalamin (ie. hydroxocobalamin, adenosylcobalamin, and cyanocobalamin), which then immediately transfers the methyl group to the homocysteine to form methionine (via methionine synthase). Thus, hydroxocobalamin, cyanocobalamin, and adenosylcobalamin are readily usable by most people. Intestinal absorption, however, is a different question.

In studies, intestinal absorption of methylcobalamin and hydroxocobalamin seems to exceed absorption of adenosylcobalamin. Methylcobalamin is only slightly better absorbed than hydroxocobalamin. Cyanocobalamin is the form of cobalamin that is predominantly used in supplementation, although methylcobalamin and hydroxocobalamin are the most absorbable forms of B12 (see below).

Following is the order of vitamin B12 absorbability from most- to least-absorbed:

  1. Methylcobalamin (best)
  2. Hydroxocobalamin (almost as well absorbed as methyl-)
  3. Cyanocobalamin (moderate)
  4. Adenosylcobalamin and Sulphitocobalamin (tie for distant last place)

Note that cyanocobalamin, the more synthetic form of cobalamin, is much better absorbed than adenosylcobalamin.

Choosing B12 Supplements

From the above, it seems that the best forms of B12 supplementation are likely methylcobalamin and hydroxocobalamin, with the deciding factor between the two being relative price. However, anecdotally, some people report better results from particular forms of B12 over other forms. People suffering from malabsorption due to inadequate stomach acid, gastritis, or pernicious anemia may need to obtain a prescription for subcutaneous B12 shots. Ask your healthcare provider for insight.

Vegetarian and Vegan Food Sources of Vitamin B12

Vitamin B12 is highly concentrated in animal foods and virtually non-existent in plant foods with the following few exceptions discussed below. Since cobalamin is an essential nutrient, it is important vegans and vegetarians understand the need for and sources of vitamin B12 in order to avoid health problems.

There is a pernicious and dangerous myth among vegans that plant and other non-animal sources of B12 are reliable and that it’s difficult to get a B12 deficiency. Nothing could be further from the truth. Jack Norris confronts this reality at VeganNutrition.org. Studies consistently show that B12 deficiency is not only common in vegetarians and vegans, but that it regularly causes them substantial damage to the nervous system.

Reliable Vegan Sources of B12

Nutritional Supplements — Regular supplementation with vitamin B12 is the safest approach to ensuring B12 intake for vegetarians and vegans. It can take years of inadequate B12 intake before symptoms appear, but deficiency is serious and can cause demyelination damage to the nervous system. Because the body absorbs minimal amounts of B12 at any one time, B12 should be consumed regularly, even if in smaller quantities at a time.

Unreliable Vegan Sources of B12

Nothing but animal food or supplements have adequate evidence for being a reliable source of vitamin B12, whether mushroom, chlorella, seaweed, ferment, or otherwise. Again, see VeganNutrition.org for an in-depth discussion.

Brewer’s Yeast — Brewer’s yeast has varying, unreliable amounts of B12. However, it can potentially be trusted if the label lists an adequate %RDA or %DV of vitamin B12 in the nutrition facts label.

Nori — Algae includes microscopic algae like chlorella and macroscopic (large) seaweeds like nori. Most edible algae contains little or no vitamin B12. Purple laver (nori) and green laver are exceptions and contain significant amounts of active B12. Edible purple laver (nori) contains primarily adenosylcobalamin, methylcobalamin, and hydroxocobalamin. Nori also contains omega-3 fatty acids, iron, and vitamin A, three nutrients vegans are often deficient in. Nori is likely the most reliable vegan/vegetarian source of active vitamin B12, yet it would require about ten average sheets of nori DAILY to provide the daily allowance for most people. To be safe, B12 sources should be varied and taken regularly to ensure reliability of intake.

Chlorella — Chlorella is a microscopic algae that—depending on the source or brand—may or may not contain substantial amounts of B12. Always check the label for B12 content, and also vary your sources of B12 in case any particular source is unreliable.

Edible Mushrooms — Mushrooms are a potential source of vitamin B12, but their content is highly variable and unreliable. Additionally, some mushrooms contain non-usable forms of B12 that actually block the action of usable B12, making the B12 essentially anti-B12. Massive amounts (50g daily) of shiitake mushrooms may barely provide the DV for vitamin B12, but again, relying on mushrooms alone for vitamin B12 is risky without directly testing their B12 content or monitoring blood markers of B12 status.

Fermented Soy — Fermentation occasionally produces usable vitamin B12. However, the content is unreliable and usually impossible to ascertain. Most ferments do not contain appreciable amounts of vitamin B12. The most promising food ferment is tempeh, a form of fermented soy. This, however, is also highly variable in content and should not be relied on for B12 intake without testing as mentioned previously.

Plants Fertilized with Manure — Eating organic plants fertilized with manure has been shown NOT to provide substantial amounts of vitamin B12.

References

Farquharson, J., & Adams, J. (1976). The forms of vitamin B12 in foods. British Journal of Nutrition, 36(1), 127-136. doi:10.1079/BJN19760063

Paul C, Brady DM. Comparative Bioavailability and Utilization of Particular Forms of B12 Supplements With Potential to Mitigate B12-related Genetic Polymorphisms. Integr Med (Encinitas). 2017;16(1):42–49.

Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Chapter 9.

Watanabe F, Yabuta Y, Bito T, Teng F. Vitamin B₁₂-containing plant food sources for vegetarians. Nutrients. 2014;6(5):1861–1873. Published 2014 May 5. doi:10.3390/nu6051861

About Nicholas Hundley, MS, CNS

Nicholas Hundley is a nutritional biochemist and certified nutrition specialist. He is the main author for the MindWhale blog at MindWhale.com. He practices nutrition and can be found at NicholasHundley.com

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