Vitamin B12 Concerns and Supplementation


By Natalie Gentile, MD and Dan Goldstein

Vitamin B12 Concerns and Supplementation

Vitamin B12 is an essential B vitamin necessary for the formation of red blood cells and DNA, as well as some physiological processes in the body.1 It is essential in that the human body is not able to manufacture it on its own and it must be taken in through diet. Without sufficient B12, nerves and cells are not able to function properly and its deficiency may cause a host of health consequences from anemia to incontinence to depression and delusions.1,2 A B12 deficient mother may also put their newborn at risk for developmental issues in addition to these conditions.3

I’ve heard for so long that B12 deficiency is an issue only for vegetarians, but in reality the only B12 deficient patients I have seen thus far are omnivores. This is a problem that can affect anyone regardless of dietary intake. In fact, it is one of the most common nutrient deficiencies.4 In one study, B12 deficiency was found in 16-17% of people who ate meat.5 Deficiency may be even more common in the elderly.6

While the situation around vitamin B12 sounds grim, luckily it often takes years for deficiency symptoms to develop. This is because our bodies are very good at retaining B12. That said, because B12 is such a critically important nutrient and its deficiency may damage health permanently, make sure to consume B12 weekly, if not daily. Do not wait for deficiency symptoms.

A misconception of vitamin B12 is that it is manufactured by animals. This is false. Animals nor plants are able to synthesize B12.7 It is actually manufactured by bacteriasome of which may be found in the guts of animals that people eat. Therefore, a certain amount of B12 may be obtained by eating animal products, however due to the various health concerns of eating these foods, I advise taking a vegan B12 supplement. Cereals fortified with vitamin B12 are another dependable source.8 A person’s ability to absorb B12 through animal sources is low and these are not very reliable sources anyway.8 People with the highest B12 levels in their blood are those who regularly take B12 supplements or eat B12 fortified food, not the people who consume the most meat.5

The easiest way to make sure you are getting enough B12 is through taking a daily supplement. 250 mcg is all the B12 that is necessary if taken each day. However, most dietary supplements contain far more of the vitamin than is necessary. Purchase the supplement with B12 content closest to 250 mcg and take it every day.

Another strategy is to take an extremely large dose of cyanocobalamin once per week. Those who choose this route would want to take a dose of 2,500 to 5,000 mcg once weekly.

Cyanocobalamin, hydroxocobalamin and methylcobalamin are the different forms of B12 found in supplements. Cyanocobalamin and methylcobalamin are the more common ones. Methylcobalamin is not as shelf stable as cyanocobalamin and has not been as heavily studied. Therefore, cyanocobalamin may be the safest bet. However, based on the research that has been done, there does not appear to be a difference in the efficacy of these three varieties.9–11 

2,500 to 5,000 or even 250 mcg is actually a lot of B12. Currently, the Daily Value for this vitamin B12 is only 6 mcg, which will officially drop to 2.4 mcg on January 1st, 2020.9 The reason I recommend taking doses that are so large in comparison to the Daily Value is because of the low bioavailability of B12. We can only absorb 1.5 to 2 mcg at a time,12 and an additional 1% of what we eat will diffuse from our gut into our bloodstream.13 A dose of at least 250 mcg per day or 2,500 mcg per week will ensure that a daily average of about 4.5 mcg is absorbed, which is the minimum amount I recommend for my patients. 

Foods fortified with B12 contain lower levels that are more reflective of this tiny Daily Value. Because these foods are intended to be eaten multiple times throughout the day, eating just 4.5 mcg, or 190% of the Daily Value (as of the 2020 Daily Values) in each sitting is adequate. If fortified foods are your predominant source of B12, space them out by four to six hours to optimize absorption.14 This is a perfectly fine option and for those who choose this route, I support the recommendation of Dr. Michael Greger (check out his incredible plethora of information at consume B12 fortified foods three times a day.15
There is no risk of vitamin B12 toxicity because it is water soluble. In other words, if you take more than your body needs, it will be excreted in your urine. Be aware that certain drugs may interfere with vitamin B12 absorption including aminosalicylic acid, metformin, colchicine and proton pump inhibitors (think Prilosec).1 Vitamin C may also inhibit absorption.1 Make sure to wait to take any of these medications or a vitamin C supplement until at least two hours after B12 supplementation.1


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