Vitamin B12 deficiency can develop when the body does not get enough vitamin B12 from food or cannot properly absorb it. Common causes include a diet low in animal-based foods, especially in strict vegetarians or vegans, poor absorption caused by stomach or intestinal disorders, pernicious anemia, previous stomach or intestinal surgery, and long-term use of certain medicines such as metformin or acid-reducing drugs. Older adults may also be at greater risk because stomach acid production can decrease with age, reducing B12 absorption.
Vitamin B12 Deficiency Causes
Vitamin B12 deficiency occurs when the body does not receive enough vitamin B12 or cannot properly absorb and use the vitamin. Because vitamin B12 is important for healthy red blood cells, nerve function, and DNA production, a deficiency can eventually affect several body systems. The causes may be related to diet, problems with absorption, certain medical conditions, previous digestive surgery, or long-term use of some medicines.
1. Low Vitamin B12 Intake
One important cause is not consuming enough vitamin B12-containing foods. Vitamin B12 occurs naturally mainly in animal-derived foods such as fish, meat, poultry, eggs, milk, and other dairy products. People who consume little or no animal-source food may therefore have a higher risk of inadequate B12 intake, particularly when fortified foods or supplements are not used.
2. Strict Vegetarian or Vegan Diet
People following a strict vegan diet do not consume natural animal sources of vitamin B12. Plant foods generally do not naturally contain B12 unless they have been fortified. Without reliable fortified foods or a suitable supplement, long-term dietary restriction can contribute to vitamin B12 deficiency.
3. Pernicious Anemia
Pernicious anemia is an autoimmune condition that can prevent the stomach from producing enough intrinsic factor. Intrinsic factor is a protein required for efficient absorption of vitamin B12. When intrinsic factor is lacking, the body may have difficulty absorbing B12 from food.
4. Stomach Problems
Conditions affecting the stomach can interfere with the normal process required to release and absorb vitamin B12. Atrophic gastritis and other disorders that reduce stomach acid or affect the cells responsible for producing intrinsic factor can increase the risk of deficiency.
5. Intestinal Absorption Problems
Vitamin B12 is ultimately absorbed in the small intestine. Disorders that affect the stomach or small intestine can therefore interfere with B12 absorption. Conditions such as Crohn’s disease and celiac disease may increase the risk of vitamin B12 deficiency.
6. Stomach or Intestinal Surgery
Some surgeries involving the stomach or small intestine can reduce the body’s ability to absorb vitamin B12. Weight-loss surgery, removal of part of the stomach, or surgery involving the section of intestine where B12 is absorbed can increase the risk of deficiency.
7. Long-Term Use of Certain Medicines
Some medicines can interfere with vitamin B12 absorption when used for a prolonged period. Examples include metformin, which is commonly used to treat type 2 diabetes, and certain acid-reducing medicines, including proton pump inhibitors. People taking these medicines for long periods may need their B12 status assessed when clinically appropriate.
8. Older Age
The risk of vitamin B12 deficiency can increase with age. Some older adults develop digestive changes, including reduced stomach acid, that can make it more difficult to absorb B12 naturally present in food.
9. Alcohol-Related Nutritional Problems
Excessive alcohol consumption can contribute to poor nutrition and may interfere with the absorption and use of several nutrients, including vitamin B12. People with heavy alcohol use may therefore have an increased risk of nutritional deficiencies.
10. Other Digestive and Medical Conditions
Several other medical conditions can affect vitamin B12 status. Problems involving the digestive tract, autoimmune conditions, and certain rare inherited disorders can interfere with B12 absorption or metabolism. Identifying the underlying cause is important because treatment depends on why the deficiency developed.
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When Should Vitamin B12 Deficiency Be Checked?
People with persistent fatigue, numbness or tingling, balance problems, unexplained anemia, digestive disorders, a restrictive diet, or risk factors affecting B12 absorption may benefit from discussing vitamin B12 testing with a healthcare professional. Neurological symptoms can occur even without anemia, so persistent symptoms should not be ignored.
