Causes, Signs and Symptoms of Vitamin B12 Deficiency

Benefits of Vitamin B12


The discovery of vitamin B12 was considered so important that the scientists won a Nobel Peace Prize in the 20th century [1]. Vitamin B12 is an essential vitamin that is crucial for healthy red blood cells, brain function and DNA synthesis. The vitamin assists in performing over 100 reactions in the human body [2].

In fact, this vitamin has an emerging role in nutritional epigenetics, where it may help activate or turn on certain genes in the human body. While the science is still extremely early, Vitamin B12 could play a role in slowing down the aging of the human body [3].

However, up to 90% of older adults are deficient in vitamin B12 [2]. This means that older adults could be at risk of compromising healthy blood cell formation, optimal brain functioning and DNA synthesis.

How much Vitamin B12 do I need per day?

The amount of vitamin B12 required each day depends on your sex and your age. Requirements are determined off population studies, where the recommended amount is estimated to meet the need of 98% of healthy individuals.

If you live with a chronic condition or take certain medications, your vitamin B12 needs can be higher or lower.

The recommended daily intake of vitamin B12 for healthy adults is 1.5 mcg per day [4].

Causes of Vitamin B12 deficiency

Not getting enough vitamin B12 through diet

Some people do not consume enough vitamin B12 in their diet, especially if they follow a vegan or vegetarian diet [5]. This is because vitamin B12 is primarily found in animal foods, like meat, eggs and milk products.

Very few plant foods naturally contain vitamin B12. Some fortified sources, including vegemite, nutritional yeast and plant-milks contain vitamin B12, but these foods are not always fortified so it’s important to read the label each time.

Older adults with malabsorption of vitamin B12

It is estimated that up to 90% of older adults are deficient in vitamin B12 [5,6]. This is linked to a reduced absorption of vitamin B12 due to less stomach acid production, or hypochlorhydria  [7].

Vitamin B12 found in foods is attached to a type of protein. To be properly digested, the acid in your stomach is required to release the vitamin from the protein. Then, special cells in your stomach release an intrinsic factor, which attaches to the vitamin to transport it into the bloodstream.

10-30% of older adults have decreased stomach acid production, which decreases their absorption of vitamin B12 from food [2].  On the other hand, Vitamin B12 from supplements does not require stomach acid to be broken down and digested. As such, the Institute of Medicine recommends that all individuals over the age of 50 supplement with vitamin B12 [9].

If a doctor realizes that the cause of malabsorption is due to the lack of the intrinsic factor, vitamin B12 supplements will not be absorbed. In this case, vitamin B12 injections will be prescribed.

Medical conditions & medications

Many medical conditions that target the digestive system can impact how vitamin B12 is digested and absorbed. These include [2]:

  • Pernicious anemia
  • Celiac disease
  • Crohn’s disease
  • Hypochloremia

Some medications can also affect the way vitamin B12 is digested and absorbed. These include:

  • Proton-pump inhibitors
  • H2 receptor antagonists
  • Metformin

Signs & symptoms of Vitamin B12 deficiency

Vitamin B12 deficiency is common in older adults, with prevalence of up to 90%. A deficiency in vitamin B12 is usually diagnosed if blood levels are less than 170 pg/ml [8].

 If vitamin B12 deficiency results in a type of anemia known as megaloblastic anemia, red blood cells may appear larger than usual on a blood test [9].

It’s important to monitor for signs and symptoms of vitamin B12 deficiency and speak with your doctor if you experience any of the following.


Early signs of vitamin B12 deficiency:

  • Fatigue and weakness
  • Constipation
  • Loss of appetite

Serious signs of vitamin B12 deficiency:

  • Numbness or tingling in hands and feet
  • Poor memory and confusion
  • Soreness in the mouth and tongue

Can I test for vitamin B12 deficiency?

Your doctor can perform a blood test to see if you have vitamin B12 deficiency. Usually, levels less than 170 pg/ml might indicate a deficiency [2].

 They may also look at the size of your red blood cells, where larger blood cells can indicate megaloblastic anemia, which is caused by a deficiency in both folate or vitamin B12.

The doctor or healthcare professional will also conduct a thorough medical history to assess your risk of vitamin B12 deficiency based on your medical conditions or medications. A dietitian may also perform a diet history to see how much vitamin B12 you are getting in through diet.


What foods are high in vitamin B12?

The recommended daily intake for vitamin B12, from both foods and supplements, is 1.5 mcg per day.

Some of the best food sources of vitamin B12 include:

  • Liver, 30 grams (70.7 mcg)
  • Salmon, 30 grams (4.8 mcg)
  • Nutritional yeast, 30 ml (2.4 mcg)
  • Milk, 250 ml (1.2 mcg)

Remember that it is recommended for older adults to consume a vitamin B12 supplement as they may have troubles digesting vitamin B12 from foods.



  1. Scott, J. M., & Molloy, A. M. (2012). The discovery of vitamin B12. Annals of Nutrition and Metabolism, 61(3), 239-245.
  2. National Institutes of Health. (2020, March 30). Vitamin B12. Dietary Supplements Factsheet.
  3. Sae‐Lee, C., Corsi, S., Barrow, T. M., Kuhnle, G. G., Bollati, V., Mathers, J. C., & Byun, H. M. (2018). Dietary intervention modifies DNA methylation age assessed by the epigenetic clock. Molecular nutrition & food research, 62(23), 1800092.
  4. Public Health England. (2016, August 01). Government Dietary Recommendations. Government recommendations for energy and nutrients for males and females aged 1 – 18 years and 19+ years.
  5. Rizzo, G., Laganà, A. S., Rapisarda, A. M. C., Ferrera, L., Grazia, G. M., Buscema, M., ... & Vitale, S. G. (2016). Vitamin B12 among vegetarians: status, assessment and supplementation. Nutrients, 8(12), 767.
  6. Wong, C. W. (2015). Vitamin B12 deficiency in the elderly: is it worth screening. Hong Kong Med J, 21(2), 155-64.
  7. Hurwitz, A., Brady, D. A., Schaal, S. E., Samloff, I. M., Dedon, J., & Ruhl, C. E. (1997). Gastric acidity in older adults. Jama, 278(8), 659-662.
  8. Hughes, C. F., Ward, M., Hoey, L., & McNulty, H. (2013). Vitamin B12 and ageing: current issues and interaction with folate. Annals of clinical biochemistry, 50(4), 315-329.
  9. National Organization for Rare Disorders. (2008, January 01). Anemia, Megaloblastic. Rare Disease Database.,%2C%20white%20cells%2C%20and%20platelets