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Vitamin B12 is important to people of all ages, but it is especially vital for the growth and development of infants and children.

Children fed a vegan diet, children who refuse to eat meat, and children with physical issues concerning vitamin B12 absorption/use are at risk for B12 deficiency. Some medications commonly prescribed to children can also put them at risk of B12 deficiency.

Infants born to vitamin B12 deficient mothers, exclusively breastfed infants of vitamin B12 deficient mothers, and infants fed homemade or inappropriately B12-fortified baby formula are all at risk of vitamin B12 deficiency. 

In this article, we’ll discuss the symptoms and causes of vitamin B12 deficiency. 

What Is Vitamin B12?

Vitamin B12 is a water-soluble essential vitamin, meaning that we must consume it regularly in our diet to be healthy. Vitamin B12 is important for red blood cell formation; nervous system growth, development, and function; DNA synthesis; immune function; and mitochondrial health.

What Are The Symptoms Of B12 Deficiency?

Vitamin B12 deficiency causes anemia, problems with the nervous system, and issues with growth and development.

A girl in a blue dress covers her cough with her elbow.Symptoms may include:

  • Tiredness, fatigue, lethargy, and/or weakness
  • Depression and irritability
  • Lowered immune function and frequent infections
  • Memory problems and confusion
  • Numbness and tingling in hands and feet
  • Nausea, vomiting, and/or diarrhea
  • Lack of appetite and weight loss
  • Sore mouth or tongue
  • Lack of coordination when walking or speaking
  • Failure to thrive in infants 
  • Delayed developmental milestones
  • Developmental regression

Most vitamin B12 deficiency symptoms can be reversed quickly with B12 supplementation. However, neurological issues that aren’t addressed promptly may eventually become permanent. 

B12 deficiency may only cause mild symptoms or may even be asymptomatic. It is often missed, so if anyone in your family has any of the risk factors described below, it would be wise to discuss periodic vitamin B12 testing with your doctor. 

What Causes Vitamin B12 Deficiency?

1. Not Consuming Enough Vitamin B12

Vitamin B12 is naturally occurring in animal products and can be found in fortified vegan products. People who consume a non-fortified vegan diet and breastfed infants born to mothers deficient in B12 are at risk for vitamin B12 deficiency.

B12 rich foodsSolution: Consume more vitamin B12-rich foods and use B12 supplements or injections until levels are healthy.

2. Low Stomach Acid Or Intrinsic Factor

Vitamin B12 is bound to protein in food. You need stomach acid and digestive enzymes to free B12 from protein so that it can be absorbed. People who have low stomach acid are at greater risk of B12 deficiency. 

Causes of low stomach acid may include:

  • Use of acid-suppressing medicine for heartburn or GERD
  • Gastritis- inflammation of the stomach lining
  • Chronic stress
  • Age over 65 years
  • Deficiency of zinc or B complex vitamins
  • H.pylori infection- H. pylori is a common cause of stomach ulcers
  • Stomach surgery, eg. gastric bypass surgery
  • Pernicious anemia causes low or absent intrinsic factor

Solution: Address the cause of low stomach acid. Consider taking a supplement that contains hydrochloric acid and digestive enzymes or digestive bitters. Vitamin B12 supplements or injections may be required.

3. Conditions Affecting Vitamin B12 Absorption

Vitamin B12 is absorbed in the end of the small intestine (aka the terminal ileum). Some digestive diseases and other factors limit the body’s ability to absorb nutrients. 

Factors that reduce the body’s ability to absorb B12 may include:  

  • Diseases that affect the small intestine’s ability to absorb efficiently, like Crohn’s disease, Celiac disease, HIV, and some parasitic infections.
  • Excessive alcohol use can impair the absorptive capacity of the intestine.
  • Intestinal surgery, eg. partial or full large intestine resection
  • Some medications can affect the absorption or utilization of vitamin B12. These include corticosteroids, metformin, anti-seizure medicine, birth control pills, certain antibiotics, gout medication, and cholesterol-lowering medication. 

Solution: Address the causes of low B12 absorption, if possible. These types of diseases are best treated with vitamin B12 injections or nasal spray which bypass the need for gastrointestinal absorption. High-dose oral supplementation may help people who still have some ability to absorb B12. 

4. Genetic Predispositions Affecting Vitamin B12 

Some genetic predispositions can affect how the body uses vitamin B12. The two most well-known genes are Transcobalamin II and 5,10-Methylenetetrahydrofolate Reductase (MTHFR). However, many other genetic polymorphisms may contribute to issues with Vitamin B12 levels.

Solution: Genetic analysis is available. Ensure that supplements contain active forms of b complex vitamins. B12 should be in the methylcobalamin, hydroxocobalamin, or adenosylcobalamin form, rather than cyanocobalamin, for optimal use. Folate should be in 5-methyltetrahydrofolate (5-MTHF) form rather than folic acid.  

How To Test For Vitamin B12 Deficiency

Vitamin B12 deficiency is assessed with blood tests. A simple measurement of vitamin B12 level is the most common test run. Your doctor may also run a complete blood count test to check for Vitamin B12 deficiency-associated anemia (aka megaloblastic anemia). Methylmalonic acid (MMA) is another useful blood test. MMA levels rise as vitamin B12 levels fall.  

In my medical practice, regular vitamin B12 testing is standard for preconception care, pregnant women, and anyone with any of the risk factors described above. 

How To Treat Vitamin B12 Deficiency

Vitamin B12 deficiency is easily treated with vitamin B12 supplements. If there is an issue with vitamin B12 absorption in the intestine, injections or nasal spray may be preferred over oral forms.

Vitamin B12 comes in four forms: methylcobalamin, hydroxocobalamin, adenosylcobalamin, and cyanocobalamin. The first three forms are found in nature and are the easiest for the body to process. In my practice, if genetic polymorphisms like MTHFR are present, I usually recommend methylcobalamin along with 5-methyltetrahydrofolate.

Vitamin B12 is an extremely safe supplement. Therefore, in my practice, I recommend people at risk of vitamin B12 deficiency take supplements to prevent deficiency. 


Vitamin B12 is essential for infants, children, and adults. A lack of B12 can cause issues with mood, energy levels, nervous system, red blood cell production, immune function, and more. It is important to consume plenty of vitamin B12-containing foods and ensure good gut health to maintain healthy vitamin B12 levels. Regular testing is a wise idea if you have risk factors for vitamin B12 deficiency. Vitamin B12 deficiency is easily treated and prevented with supplementation. 


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Dr. Green Mom

Dr. Mayer is a naturopathic medical doctor and an expert in nutrition and wellness as it relates to pediatrics and families. Her passion for prevention of disease as cure fueled her desire to immerse herself into specializing in adult onset chronic conditions, as well as childhood chronic illness.

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