ADEQUATE VITAMIN B12 » on a plant-based lifestyle

Vitamin B12: Function

Vitamin B12 has many roles. It helps convert the macronutrients (carbohydrates, fats and proteins) into energy. It's required for DNA synthesis, which then means it's an especially important vitamin during growth. It's required for red blood cell production and it also helps to maintain the protective coating around our nerves called the myelin sheath.

In some high-protein foods we consume, there is an amino acid called methionine. The breakdown of methionine creates another amino acid by-product called homocysteine. This homocysteine can damage the delicate linings of our arteries and can trigger heart disease. Excess homocysteine can also negatively impact bone health. Vitamin B12 helps the body to get rid of this damaging homocysteine.

Recommended Intake

The official Recommended Dietary Allowance (RDA) for adults over 14 years of age is 2.4 mcg per day, so you can see the body requires only very small amounts. However some recent studies suggest intakes of 4-7 mcg may help protect against high levels of homocysteine.

The Institute of Medicine concluded “no adverse effects have been associated with excess vitamin B12 intakefrom food and supplements in healthy individuals”. Therefore, no Upper Limit has been set for this vitamin.

How to Get Enough

Indeed, vitamin B12 is recommended for those following a plant-based lifestyle. There are a few ways to make sure your intake is adequate (1):

  1. Daily (food): Consume 3 servings of vitamin B12 fortified foods, with each serving offering at least 2 micrograms (mcg) of vitamin B12. Some foods that may be fortified are non-dairy milks, vegan meat substitutes, breakfast cereals, and bars. Be sure to read the labels to determine how much vitamin B12 is in the product, if at all. Note it is best if these foods are eaten at different times of the day as vitamin B12 receptors can become saturated with as little as 1.5 mcg doses; in other words, if more is taken at once the body simply cannot absorb it all. It may be wise to combine both dietary intake with a supplement, as the amount in these foods and intake of these foods can vary.

  2. Daily (supplement): Take a vitamin B12 (cyanocobalamin) supplement daily that offers at least 25 mcg of Vitamin B12. If you're taking a multivitamin supplement, be sure to check the label as this amount or more may be provided. Some experts suggest a larger dose for those who are up to 65 years of age, aiming for 250 mcg per day, while seniors may require 500-1000 mcg per day due to excess excretion.

  3. Twice Weekly (supplement): Take a vitamin B12 (cyanocobalamin) supplement two times per week that offers 2000-2500 mcg of vitamin B12. Note that although our daily needs for vitamin B12 is much less than this, the body only absorbs a fraction of that offered by a supplement. The less frequently vitamin B12 is taken, the higher the needed dose.

Two Forms of Vitamin B12 Supplements - Which to Take?

There are both cyanocobalamin supplements and methylcobalmin supplements. Let's briefly review both (1):

Cyanocobalamin: this form of vitamin B12 has been more extensively research and is the most stable form. Indeed, a small amount of cyanide is present to help stabilize the vitamin. This has been a source of hesitation for those purchasing this form of vitamin B12 supplement, however, cyanide is naturally present in nature. For example, 1 Tbsp of flax seeds has 30x as much, and this amount has been deemed insignificant by toxicologists. After consumed, the body removes and detoxifies the cyanide. The body then naturally converts the cyanocobalamin to methalcobalamin: the more active form of vitamin B12. Note: this conversion may be more difficult in those who smoke or have kidney failure; in this case a direct source of methylcobalamin may be best.

Methylcobalamin: this co-enzyme form of vitamin B12 is less stable, and less research has been done to determine its effectiveness. Some sources indicate high doses would be needed to have the same affect as cyanocobalamin - as much as 1000 mcg per day.

Commonly Asked Questions

  1. What supplement type should I take? Liquid supplement, sublingual tablets (placed under the tongue to dissolve), as well as regular tablets to swallow or chew are all suitable.

  2. What if I take too much? When we take larger doses, the body only absorbs a fraction of that offered because the receptors become saturated (i.e. cannot absorb more). So there is no concern that too much is being taken. Vitamin B12 is a water-soluble vitamin, meaning any excess above and beyond what the body needs will simply be excreted in the urine.

  3. What if I miss a dose? What do deficiency symptoms look like? The body is phenomenal at re-absorbing Vitamin B12. If you happen to go a period of time without supplement, or you have been vegan for a few months and have not been supplementing, this should not be a cause for concern. Short-term deficiencies can be remedied; however, long-term deficiencies can cause irreversible damage in the body. Early symptoms of deficiency include weakness, fatigue and mood changes and can be easily confused for other causes so it is important to supplement regardless, and not rely on symptoms to indicate if intake is low.

  4. Aren't these foods reliable sources of vitamin B12? Fermented foods, sprouts, mushrooms, seaweed, spirulina, sprouts, raw plant foods are unreliable sources. Although some sources say vitamin B12 is present in such foods, these are most often inactive analogues and should not be considered reliable sources for this essential vitamin.

  5. Doesn't my body make vitamin B12? Indeed, our body does make some vitamin B12 naturally in the mouth and lower bowel, but the amounts made in our mouths are insufficient, and those made in the lower bowel are too low in the digestive tract to be absorbed, so it is simply excreted in the feces.


Note all references are linked in text, with the exception of:

(1) Davis, Brenda & Melina, Vesanto. (2014). Becoming Vegan Comprehensive Edition: The Complete Reference to Plant-based Nutrition. Summertown, Tennessee: Book Publishing Company, 2014. Print.

Want To Learn More?

Read this previous nutrition article called VITAMIN D & NUTRITION » do you need supplements?

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❤ Written by: Sadia