Everything You Need To Know About B12 Deficiency + How To Get Enough

Functional Medicine Doctor By Amy Myers, M.D.
Functional Medicine Doctor
Amy Myers, M.D. is a renowned leader in functional medicine living in Austin, Texas. She is a New York Times best-selling author of both The Autoimmune Solution and The Thyroid Connection, and received her doctorate in medicine from the LSU Health Sciences Center.
What To Know About B12 Deficiency + How To Get It In Your Diet

Vegetarians and vegans are not the only ones who can develop a Vitamin B12 deficiency. Whether you're young or old; paleo, gluten-free, or just a raw foods enthusiast, you too can suffer from this.

What is B12?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin required for many reactions in your body as well as for the health of your nerves, red blood cells, and DNA. Its most important role is as a methyl group donor, which is a crucial step in many of our main detoxification pathways.

B12 has many forms, and the most common are cyanocobalamin and methylcobalamin (methyl-B12). Cyanocobalamin is commonly found in supplements and energy drinks. However, in order for our bodies to use it, cyanocobalamin must be converted into methylcobalamin.

To make matters more complicated, about 50% of the population is estimated to have at least one mutation at the MTHFR gene and 10% has two mutations, meaning they're less able to methylate B12 or convert cyanocobalamin to methylcobalamin. (I personally have two gene mutations.) In fact, the more mutations one has at this gene, the less able one is to make this conversion, requiring supplementation with Methyl-B12, Folate, and B6.


Common Signs of B12 Deficiency:

  • Weakness, fatigue or low energy
  • Shortness of breath
  • Heart palpitations
  • Loss of appetite
  • Digestive issues such as diarrhea or constipation
  • Frequent bruising or bleeding
  • Anemia
  • Depression or mood issues
  • Numbness and tingling in hands or feet
  • Brain fog, memory loss, confusion, dementia

Sometimes B12 deficiencies can be overlooked and misdiagnosed as other disorders. One study even found a link between low B12 levels and an increased risk of Alzheimer’s disease, vascular dementia, and Parkinson's disease.

Best sources of B12

Our bodies do not make vitamin B12, which means that we must get it through our diet or through supplementation. The average adult needs 2.4 micrograms a day, and the best dietary sources of vitamin B12 are animal products such as:

  • Meat
  • Poultry
  • Fish
  • Eggs

Vegan sources of B12 include nutritional yeast, algae, and seaweed, but studies have shown that these sources have little to no effect on B12 blood levels.


Common Causes of B12 Deficiency

The absorption, assimilation and methylation of B12 is a very complex process, which leaves many opportunities for error. For this reason, even those who consume sufficient amounts of vitamin B12 in their diets could still have a functional B12 deficiency. Some causes of B12 deficiency are:

  • Vegan and vegetarian diets
  • MTHFR gene mutations
  • Pernicious anemia
  • Autoimmune diseases such as Graves’ disease and systemic lupus erythematosus
  • Intestinal inflammation from Crohn's or celiac disease
  • Excessive alcohol consumption
  • Small Intestine Bacterial Overgrowth (SIBO) and leaky gut
  • Low stomach acid from prolonged use of stomach acid-reducing drugs
  • Bariatric surgeries

How to test for B12 deficiency:

  1. Complete Blood Count (CBC): This test, when it reveals the red blood cells to be very large, can indicate megaloblastic anemia, which is caused by a B12 and/or folate deficiency. Note that this doesn't always reflect how well the body is able to use B12—as it doesn't account for individuals with mutations at the MTHFR gene, for example.
  2. MTHFR genetic test: The more mutations one has to this gene, the more they require B12, folate, and B6 for their detoxification pathways and body to function optimally. It's estimated that those with one mutation decrease their ability to methylate by 30% and those with two mutations decrease their ability to methylate by 70%, making it virtually impossible get adequate B12 from diet alone.
  3. Homocysteine test: Very low or high blood levels of homocysteine can indicate a B12, folate, and/or B6 deficiency.
  4. Methylmalonic acid test: This measures the B12 stored in tissues, which makes it more specific to B12 deficiency than the other blood tests
  5. Organic Acid Test: This is a test frequently ordered by a Functional Medicine physician to determine how well an individual is able processes, methylate and functionally use B12. I use this test most frequently on those with one or more MTHFR mutations.

How do I get more B12?

Eat a diet rich in animal protein

Individuals without dietary restrictions or MTHFR mutations can simply consume more meat, fish, poultry, and eggs in their diets. You may also consider taking a high quality multivitamin with methyl-B12.

Consume a high-dose oral supplement of methylcobalamin (methyl-B12)

This option is a MUST for those with mutations at the MTHFR gene. This is also recommended for vegetarians, vegans, the elderly, and anyone else with low levels of B12. When looking for B12 supplements in the store, be sure to look for it in the form of methylcobalamin instead of cyanocobalamin. Methyl-B12 is the best form for the body to utilize and will have the greatest impact on your B12 levels.


Take sublingual methyl-B12 drops

A sublingual supplement of B12 is recommended for those with SIBO or other gut issues affecting absorption.

Get B12 shots

These are recommended for those with pernicious anemia or severely depleted B12 levels. Methyl- B12 can be injected directly into the muscle tissue to accelerate absorption and replenish muscle stores.

How do I treat B12 deficiency?

  • Optimize nutrition
  • Heal your gut if it's unhealthy
  • Check MTHFR genes and supplement if one or more mutations
  • Test CBC (Complete Blood Count)
  • Ask your doctor to run Organic Acid Test
  • Supplement if necessary

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