What Causes Vitamin B12 Deficiency?

Jun 08, 2022 Vitamin B 6 MIN

What Causes Vitamin B12 Deficiency?

Quick Health Scoop 

  • Vitamin B12 (one of eight types of vitamin B) is an essential nutrient that is important for red blood cell formation, among other supports. 
  • Some groups may be prone to low vitamin B12 levels, namely older adults, vegetarians and vegans, and those who lack intrinsic factor to absorb this vitamin (also called pernicious anemia) [1]. 
  • Signs of a vitamin B12 deficiency may include fatigue, weak muscles, and decreased appetite. 
  • Without vitamin B12, your body cannot make enough healthy red blood cells—which may result in a condition known as vitamin B12 deficiency anemia [2]. 
  • The best way to increase your intake of vitamin B12 is through a diet that includes animal products and/or fortified foods.  

If you’re curious about vitamin B12 and why this B vitamin is important for your health, then you’ve come to the right place. Vitamin B12 (cobalamin) is an essential nutrient that your body regularly needs. This vital B vitamin helps turn the food you eat into cellular energy that your body can use all day long. It also helps support your nervous system and is important for normal red blood cell formation. That’s a lot of heavy lifting for one vitamin! The daily recommended amount (RDA) of vitamin B12 is 2.4 mcg for adults, 2.6 mcg for pregnant women, and 2.8 mcg for lactating women. Low levels of this type of vitamin B in your body might lead to enlarged red blood cells that are underdeveloped. This condition, known as megaloblastic anemia, is a sign of a vitamin B12 deficiency [1]. 

What Causes Low Vitamin B12 Levels? 

First, it’s important to understand that our bodies need vitamin B12, but we don’t naturally produce it. This means our intake must come from food sources (meat, fish, dairy, fortified foods). The body can store between 1 to 5 mg of vitamin B12 in the liver for a few years. Unfortunately, that means low B12 levels might not become apparent until years later [1]. Recent studies suggest that approximately 6% of older adults, those above 60, have deficient levels of vitamin B12 and over 20% have low levels [3]. But a deficiency can occur at any age, as nearly 4% of adults aged 40-59 and 3% aged 20-39 were found to have deficient vitamin B12 levels [2]. 

Here are some reasons why some may be low in vitamin B12 [2]: 

  • Diet low in vitamin B12. People who do not regularly consume foods high in B12 (animal products and fortified foods) may not meet the RDA for vitamin B12 and are therefore at risk for low levels and/or a vitamin B12 deficiency.▲  
  • Pernicious anemia. This condition, though rare, is when a person’s stomach does not make intrinsic factor—a protein that aids the digestive system in absorbing vitamin B12 after it has been separated from food by the acids in your stomach.  
  • Gastritis. When the stomach lining becomes inflamed (gastritis) it may cause a vitamin B12 deficiency due to the lack of acids in the stomach to absorb the vitamin. 
  • Alcohol use. Alcohol affects the digestive system and may prohibit B12 absorption. 
  • Digestive issues. Certain digestive issues, such as Crohn’s disease and celiac disease, may also affect B12 absorption. 
  • Recent surgery. Those adults who have had surgery that affects the gastrointestinal system, such as a gastric bypass, might have trouble absorbing vitamin B12. 

How is a Vitamin B12 Deficiency Related to a Vitamin B9 (Folate) Deficiency? 

Vitamin B9 is another essential B vitamin. We ingest it from food (as folate) or dietary supplements (as folic acid). A folate deficiency may occur when not enough B9 is ingested from the diet, from poor absorption of nutrients by the body, or in pregnant women who are not consuming enough folate to meet their increased nutrient needs [4]. However, both vitamin B9 and B12 are involved in the process of making red blood cells, which is why a surplus of B9 (folate/folic acid) might mask a low vitamin B12 level. It’s best to check in with your healthcare provider to ensure you have adequate levels of both essential nutrients. 

What are the Signs of Low Vitamin B12 Levels? 

As we stated above, if your body has adequate levels of vitamin B9, or even a surplus, then you might not be aware that you are not getting enough vitamin B12 from your diet. Here are some signs to look out for that might indicate low B12 levels in the body [2]: 

  • Feeling more tired than usual 
  • Feeling less hungry than usual 
  • Unexpected weight loss 
  • Yellowish skin 
  • Muscle weakness 
  • Feeling more irritable than usual 
  • Difficulty focusing 

If you think you might have a diet lacking in essential nutrients like vitamin B12, then it’s best to consult with your healthcare provider to check your nutrient levels. 

How To Increase Your Daily Amount of B12 

The good news is that a vitamin B12 deficiency can be remedied. The best way to obtain vitamin B12 is through food, and that includes a diet high in animal products such as meat, fish, eggs, and dairy, as well as foods fortified with vitamin B12 such as breakfast cereals, non-dairy milk, and nutritional yeast.  

Those adults that may need more vitamin B12 might be suggested to take high-dose dietary supplements or vitamin B12 injections, as they provide a high strength dose of B12 [1]. You should consult with your healthcare provider before considering any dietary supplements. 

The Bottom Line 

Vitamin B12 is vital for the formation of red blood cells in our body. An inadequate intake of vitamin B12 may lead to a deficit of healthy red blood cells, which may result in a condition called megaloblastic anemia [3]. It is important to ensure you are getting enough vitamin B12 from your diet so this essential nutrient can do its job! 


Learn More About Essential Nutrients: 

  Approximately 6% of older adults have deficient levels of vitamin B12 and over 20% have low levels [3] 

This information is for educational purposes only and is not intended to serve as medical advice or a recommendation for any specific product. Consult your health care provider for more information.  


  1. National Institutes of Health. “Office of Dietary Supplements - Vitamin B12.” U.S. Department of Health and Human Services. Accessed on 9 May 2022. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/.  
  1. Cleveland Clinic. “Vitamin B12 Deficiency: Symptoms, Causes & Treatment.” Accessed on 17 May 2022. https://my.clevelandclinic.org/health/diseases/22831-vitamin-b12-deficiency.  
  1. Porter, Kirsty, et al. “Causes, Consequences and Public Health Implications of Low B-Vitamin Status in Ageing.” Nutrients, MDPI, 16 Nov. 2016, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5133110/.  
  1. Harvard T.H. Chan School of Public Health. “Folate (Folic Acid) – Vitamin B9.” The Nutrition Source, 2 July 2019, https://www.hsph.harvard.edu/nutritionsource/folic-acid/#:~:text=However%2C%20an%20upper%20limit%20for,B12%20deficiency%20is%20more%20common.  


Amy Mills Klipstine

NatureMade Sr. Copywriter

Amy has an MFA in Creative Writing from Antioch University in Los Angeles and is a credentialed English teacher, though she left the classroom to write full time. She especially enjoys creating educational content about health, wellness, and nutrition. Her happy place is in the kitchen, and when not writing, you can find her trying out “kid-friendly recipes” and “healthy desserts for chocolate lovers” from her Pinterest board.

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Lynn M. Laboranti, RD

Science and Health Educator

Lynn is a Registered Dietitian (R.D.) and is a member of the Medical and Scientific Communications team at Pharmavite. She has over 20 years of experience in integrative and functional nutrition and has given lectures to health professionals and consumers on nutrition, dietary supplements and related health issues. Lynn frequently conducts employee trainings on various nutrition topics in addition to educating retail partners on vitamins, minerals and supplements. Lynn has previous clinical dietitian expertise in both acute and long-term care, as well as nutrition counseling for weight management, diabetes, and sports nutrition. Lynn earned a bachelor’s of science in Nutrition with a minor in Kinesiology/Exercise Science from The Pennsylvania State University. She earned a M.S. degree in Human Nutrition from Marywood University in Scranton, Pennsylvania. Lynn is an active member of the Academy of Nutrition and Dietetics, Sports Cardiovascular and Wellness Nutritionists, Dietitians in Functional Medicine, and holds a certification in Integrative and Functional Nutrition through the Academy of Nutrition and Dietetics.

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