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What You Need to Know About Vitamin B12

Vitamin B12

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is needed for a variety of functions within the body. Unlike many other B vitamins that are found in many plant-based foods, this vitamin is found in animal-based foods, such as meat, chicken, fish and dairy. It is also added to fortified foods like cereals and grains. Fruits and veggies do not contain any vitamin B12 unless manure, or bacteria that produce B12 have contaminated it.1

What Is the Role of Vitamin B12 in Our Bodies and What Happens When We Are Deficient?

Vitamin B12 is a complex, essential nutrient that is needed for the formation of red blood cells and DNA, cellular metabolism and neurological function. It’s also needed for fatty acid metabolism and may play a roll in depression as well.2,3

The majority of the population has adequate B12 levels and luckily, unlike other water-soluble vitamins, B12 actually is stored in the body for prolonged periods of time. In fact, for some, a deficiency can sometimes take several years to develop! Unfortunately, this is not the case for all, and some people are at heightened risk of deficiency.

Deficiency can result in a myriad of symptoms that impact the neurological, cutaneous and gastrointestinal systems. Cognitive impairment, irritability, anemia, glossitis, jaundice and vitiligo are all signs of deficiency. Further, maternal deficiency can lead to neural tube defects, anemia and failure to thrive in infants.1

Screening for deficiency can be done on routine blood work assessing for anemia. If a person’s blood work is suggestive of a type of anemia called megaloblastic macrocytic anemia, it is important to determine if this is caused from low B12 or low folate levels, as high levels of folate can actually mask a B12 deficiency. In order to rule out deficiency, additional testing is likely necessary.4

There are several groups of people who are considered high risk for deficiency, and therefore should consider taking a supplement for B12:

1. Those who follow a strict vegan diet: Since vitamin B12 is found in animal products, people who follow a vegan dietary pattern should take a supplement. It is important to mention that woman who are vegan and are lactating also place their infant at high risk of deficiency. Therefore, supplementation for mom may be necessary to prevent abnormal development of skin and hair, anemia and weak muscle tone in her infant.5

2. Patients who have had bariatric surgery or gastrectomy. People who have undergone bariatric surgery or have had part or all of their stomach removed (gastrectomy) are at increased risk of deficiency. Fortunately, this can be prevented with lifelong supplementation. For those who underwent a gastrectomy, giving intramuscular injections (IM) can prevent deficiency.2,3

3. Individuals who have pernicious anemia. People with pernicious anemia have B12 deficiency due to an autoimmune process that inhibits absorption of this vitamin. In this disease, the body destroys the gastric cells (specifically gastric parietal cells) that produce intrinsic factor, which is needed for absorption in the terminal ileum. Luckily, deficiency can be treated orally or with a B12 shot.2

4. People who are taking certain medications. Long term use of certain medications including metformin, proton pump inhibitors (PPIs) and H2 receptor antagonists interfere with absorption and metabolism, and can ultimately lead to B12 deficiency. Since metformin is often prescribed in people who have pre-diabetes or diabetes to control blood sugar, and PPIs (examples include omeprazole and pantoprazole) and H2 blockers are used to treat heartburn, many people are on these medications, placing them at increased risk for deficiency.4

5. Older adults. In the United States, the risk of deficiency increases from 6 percent to almost 20 percent once a person hits 60 years of age. This can occur because as you age, the amount of acid in your stomach decreases, which is needed for the B12 to be released from the food. Reduced acid in the stomach that occurs in advanced age can also be caused from increased usage of antacids, increased microbial growth and H. pylori infection.6,7

6. Those who have heavy alcohol intake. Alcohol has been shown to negatively impact B12 metabolism in the body. This, in addition to decreased intake of vitamin B12 rich foods in people who consume high amounts of alcohol make heavy consumption a risk factor for depleted B12 levels.6

How Can Vitamin B12 Deficiency Be Fixed?

Vitamin B12 deficiency can be fixed by giving the supplemental form of B12, which in the United States is usually cyanocobalamin. Vitamin B12 can be repleted orally or IM as well as through a nasal spray, and many routes of administration come in different doses. The dosing and timing of supplementation changes based on which type of treatment is recommended by your health care provider. Typically, it is treated with 1 mg for the first week, which is then followed by lower dosages for a month. However, if deficiency is due to malabsorption or pernicious anemia, IM or nasal spray may be warranted.

For those who are at risk of deficiency, it is a good idea to start eating foods that contain B12 to keep the level up. Although B12 is found in animal-based foods, the good news for those who follow a vegan diet is that many plant-based foods are fortified with B12. You can find B12 in most over the counter multivitamins or B-complexes, but they all contain different levels. Gummies and tablets are available, and so are sublingual tablets, like Frunutta, that dissolve right under the tongue and go right into the bloodstream, bypassing the stomach. Although the RDA (recommended daily allowance) for adults is 2.4 micrograms, many vitamin formulations come in much higher doses. Not to worry though, higher doses appear to have a good safety profile since our bodies absorb what we need, and excretes the rest.1,2


1 Langan RC, Goodbred AJ. Vitamin B12 Deficiency: Recognition and Management. Am Fam Physician. 2017 Sep 15;96(6):384-389. PMID: 28925645.

2 Vitamin B12: Fact sheet for professionals. Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional. Accessed Jan. 9, 2021.

3 Laufer EM, Hartman TJ, Baer DJ, Gunter EW, Dorgan JF, Campbell WS, Clevidence BA, Brown ED, Albanes D, Judd JT, Taylor PR. Effects of moderate alcohol consumption on folate and vitamin B(12) status in postmenopausal women. Eur J Clin Nutr. 2004 Nov;58(11):1518-24. doi: 10.1038/sj.ejcn.1602002. PMID: 15138463.

4 Miller JW. Proton Pump Inhibitors, H2-Receptor Antagonists, Metformin, and Vitamin B-12 Deficiency: Clinical Implications. Adv Nutr. 2018;9(4):511S-518S. doi:10.1093/advances/nmy023.

5 Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-. Vitamin B12. [Updated 2021 Oct 18]. Available from: www.ncbi.nlm.nih.gov/books/NBK534419/.

6 Ankar A, Kumar A. Vitamin B12 Deficiency. [Updated 2021 Jun 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: www.ncbi.nlm.nih.gov/books/NBK441923/a. doi:10.1001/archinte.1955.00250100097010.

7 Andrès E, Loukili NH, Noel E, et al. Vitamin B12 (cobalamin) deficiency in elderly patients. CMAJ. 2004;171(3):251-259. doi:10.1503/cmaj.1031155.

Dr. Nicole Avena is a research neuroscientist and expert in the fields of nutrition, diet and addiction, with a special focus on nutrition during early life and pregnancy. Her research achievements have been honored by awards from several groups including the New York Academy of Sciences, the American Psychological Association, and the National Institute on Drug Abuse. She is an assistant professor of neuroscience at the Ichan School of Medicine at Mount Sinai, in New York, NY and is a visiting professor of health psychology at Princeton University in New Jersey. Dr. Avena has written several books, including What to Eat When You’re Pregnant and What to Feed Your Baby and Toddler. She regularly appears as a science expert on the Dr. Oz Show, Good Day NY and The Doctors, as well as many other news programs. Her work has been featured in Bloomberg Business Week, Time Magazine for Kids, The New York Times, Shape, Men’s Health, Details, as well as many other periodicals. Dr. Avena blogs for Psychology Today, is a member of the Penguin Random House Speakers Bureau and has the No. 2 most watched TED-ED Health talk, “How Sugar Affects Your Brain.” You can follow Dr. Avena on Twitter (@DrNicoleAvena), Facebook (www.facebook.com/DrNicoleAvena) and Instagram (@drnicoleavena), or visit www.drnicoleavena.com.