10 Causes Of Vitamin B12 Deficiency: Are You At Risk?

Nearly two-fifths of the US population has a marginal amount of vitamin B12 (cobalamin) in their body, putting them at a high risk of a deficiency.1 You may think that the quick fix to a vitamin B12 deficiency is to eat foods that are rich in B12, but the solution may not be as simple. A B12 deficiency can be caused not only by inadequate amounts of the vitamin in the diet but also by poor absorption in the gut. Here’s a roundup of all the factors that may cause (or increase your risk of) vitamin B12 deficiency.

1. Veganism Or Vegetarianism

Since most sources of vitamin B12 are animal products, like meat or milk, vegans need to be extra-vigilant about vitamin B12 deficiency. In fact, it is so common among vegans that some people believe the escalation in the number of vitamin B12 deficiency cases is because of the popularity of veganism.


When 40 research studies were analyzed on the prevalence of the deficiency among people, higher deficiency prevalence was found in vegans than in vegetarians. However, all vegetarians should be periodically screened for the deficiency.2

[pullquote]For vegans, the skin of white button mushroom is the only natural source of absorbable B12. Other sources include fortified foods and supplements.[/pullquote]


Do note that since the liver stores this vitamin, if you go vegan or stop eating vitamin B12 foods, your B12 stores can last for 3 to 5 years.3 The symptoms of B12 deficiency will start showing up after that period.

While there are many vegetarian products like spirulina (blue-green algae) that are marketed as good sources of vitamin B12, some researchers have found them to be bogus. They have also found that the process of cooking and storing can, in fact, destroy the vitamin.4


2. Heavy Drinking

Functional vitamin B12 deficiency is associated with alcohol abuse. This deficiency is more prominent in heavy drinkers and those with an alcoholic liver disease. A functional deficiency means that while the amount of B12 found in blood is within the normal range, B12 is not metabolized.5

3. Long-Term Intake Of Antacids

If you have gastrointestinal disorders like heartburn, peptic ulcer, or acid reflux, you may be prescribed antacids. Antacids neutralize the effect of stomach acids. But your body needs gastric acid to activate certain enzyme reactions to absorb vitamin B12. Hence, using  antacids on a long-term basis may result in the malabsorption of vitamin B12.6


4. Weight Loss Surgery

Vitamin B12 deficiency is seen very commonly among people who have had a bariatric surgery. There are 2 types of bariatric surgery – gastric bypass where a portion of the stomach is made into a small pouch and attached to the distal segment of the small intestine; and restrictive techniques like gastric binding where a restriction is created in the stomach to limit the food intake of the patient.

[pullquote]A gastric bypass surgery decreases the secretion of stomach acids and a protein called IF (intrinsic factor) both of which are important for B12 absorption.[/pullquote]


Gastric bypass surgery often leads to malabsorption of nutrients, one of them being vitamin B12.7 In fact, a study noted that 30% of the participants had a B12 deficiency even after 3 years of the gastric bypass surgery. This is because the stomach secretes a protein called the intrinsic factor (IF) which must bind to vitamin B12 to make it absorbable in the small intestine. Gastric bypass decreases the production of IF as only a small portion of the stomach is available to secrete the protein. This, in turn, leads to poor absorption of B12.

5. Atrophic Or Autoimmune Gastritis

Gastritis is the inflammation or erosion of the stomach lining and it can be of 2 types – atrophic or autoimmune. Both conditions destroy the cells of the stomach lining and reduce the production of hydrochloric acid, thereby affecting the absorption of vitamin B12 from food.8 You might have to take B12 supplements to mitigate the deficiency since the gastritis diet may exclude meat and milk products, except yogurt.


6. Pernicious Anemia

[pullquote]People with pernicious anemia are given B12 injections to bypass gastric absorption.[/pullquote]

A condition where your body produces abnormally large non-functional red blood cells, pernicious anemia is both a risk factor and a complication of B12 deficiency. Pernicious anemia is an autoimmune condition where your immune cells attack the lining of your stomach that secretes the gastric intrinsic factor. Without IF, vitamin B12 cannot be absorbed properly and this leads to a deficiency. This condition mainly affects people over 60 years of age and those with a family history of at least 3 autoimmune conditions (Addison’s disease, vitiligo, or pernicious anemia).9


7. Malabsorption Of B12 In The Small Intestine

Many stomach and intestinal diseases can affect cobalamin (or vitamin B12) absorption in the small intestine. Some of them are as follows.

  • Small intestine bacterial overgrowth (SIBO): The harmful bacteria use the available B12 before it has been absorbed by the small intestine, thereby leading to a deficiency.10
  • Celiac disease: This autoimmune condition characterized by gluten allergy affects the lining of the small intestine, causing malabsorption of vitamin B12.11
  • Crohn’s disease: This condition is characterized by a damaged ileum – a section of the small intestine responsible for vitamin B12 absorption.12
  • Tapeworm infection: Tapeworms in your stomach feed off the vitamin B12 before it has been absorbed by the intestine. To avoid a B12 deficiency due to tapeworms, make sure you avoid eating undercooked meat or fish.

8. Breastfeeding By A B12 Deficient Mother

Vitamin B12 deficiency is very common in infants born to vegan or vegetarian mothers. A study has shown that the prevalence of the deficiency among infants is about 45%.13

Both unborn and newborn babies have a special need for vitamin B12 and if the mother is a vegetarian or a vegan, this need may not be met either through her diet for the unborn or through her breast milk for the newborn. As a consequence, vitamin B12 deficiency may develop in a breastfed infant within 3–6 months of age, severely affecting the baby’s growth.14

9. Age Above 50 Years

Studies have shown that the chances of vitamin B12 deficiency increase with age. An estimated 10–15% of people above 60 are found to have this deficiency.15 With age, the decrease in stomach acid secretion and the quantity of the digestive enzyme pepsin results in diminished absorption of vitamin B12.16 Older people with gastrointestinal problems are more susceptible to the deficiency.17

[pullquote]You may be at an increased risk of vitamin B12 deficiency if you are over 50 years of age and suffer from gastrointestinal problems. Deficiency is common even in people with dementia.18[/pullquote]

People over 50 years of age may show neurological changes due to vitamin B12 deficiency, resulting in increased cases of nerve and mental disorders among the elderly. Other than this, vitamin B12 deficiency in the elderly has been associated with many health problems like elevated blood levels of homocysteine that could increase their chances of developing heart disease, stroke, and Alzheimer’s.19

10. Genetic Factors

It has been identified that vitamin B12 absorption could be the result of a hereditary gene mutation. In a study conducted on 154 families suspected of hereditary cobalamin (B12) malabsorption, 126 families were found to have 1 of the 3 genes – CUBN, AMN, and GIF – mutated. The mutated genes can not only inhibit B12 absorption but also lead to abnormalities in the blood and brain.20

If you lack B12 in your diet, you can easily fix it by consuming B12-rich foods such as eggs, milk, cheese, milk products, meat, fish, shellfish, and poultry. If your B12 deficiency is due to poor absorption, you can take supplements. But first make sure to get treatment for the root cause as a prolonged cobalamin deficiency can lead to health complications like heart disease, Alzheimer’s, and infertility.