Which Group is at Greatest Risk for Vitamin B12 Deficiency?

November 23, 2025 •

4 min read

According to the National Institutes of Health, pernicious anemia is the most common cause of clinically evident vitamin B12 deficiency worldwide. Understanding which group is at greatest risk for vitamin B12 deficiency is crucial for early detection and prevention of serious health complications, especially since many factors can interfere with absorption.

Quick Summary

Several groups face a heightened risk of vitamin B12 deficiency, including older adults, vegans, those with pernicious anemia, and people who have had gastrointestinal surgery. Other high-risk individuals include those with conditions like Crohn's or celiac disease and those using certain medications like metformin or proton pump inhibitors. Understanding these risk factors is vital for prevention and management.

Key Points

Older Adults: The elderly are at high risk due to age-related malabsorption, often caused by conditions like atrophic gastritis that reduce stomach acid and intrinsic factor production.
Pernicious Anemia: This autoimmune disease is a leading cause of severe B12 deficiency globally, requiring lifelong injections because the body cannot produce intrinsic factor.
Vegans and Vegetarians: People who eat little to no animal products, the primary source of B12, are at high risk and must rely on fortified foods or supplements to avoid deficiency.
Gastrointestinal Conditions: Diseases like Crohn's and celiac disease, as well as surgeries such as gastric bypass, impair the absorption of B12 in the small intestine.
Certain Medications: Long-term use of acid-reducing drugs (PPIs) and the diabetes drug metformin significantly increases the risk of B12 deficiency by interfering with absorption.

Older Adults and Reduced Absorption

Older adults represent a significant demographic at risk for vitamin B12 deficiency, with some studies showing deficiency rates in community-dwelling older adults ranging from 3% to 43% depending on the diagnostic criteria used. This risk primarily stems from malabsorption rather than poor dietary intake. A condition known as atrophic gastritis, which involves chronic inflammation of the stomach lining, is a common culprit. This inflammation reduces the stomach's production of hydrochloric acid and a protein called intrinsic factor, both of which are essential for releasing B12 from food and absorbing it in the small intestine. The diminished stomach acid prevents the initial separation of B12 from food proteins, while the lack of intrinsic factor inhibits its final absorption. Furthermore, some studies show that Helicobacter pylori infection, which is prevalent in older individuals, can also lead to atrophic gastritis and further contribute to this malabsorption.

Vegans and Strict Vegetarians

Since vitamin B12 is naturally found almost exclusively in animal products, individuals following a vegan or strict vegetarian diet are at a high risk for deficiency if they do not supplement properly. While the body can store B12 for several years, relying solely on unfortified plant-based foods will eventually deplete these reserves. This risk also extends to infants of vegan mothers who are exclusively breastfed, as the mother's low B12 status directly impacts the vitamin content of her breast milk. Infants have very limited B12 reserves and can develop serious neurological damage and developmental delays if the deficiency is not detected and treated early.

Individuals with Pernicious Anemia

Pernicious anemia is a particularly high-risk condition and a common cause of vitamin B12 deficiency. It is an autoimmune disorder where the immune system attacks the stomach cells responsible for producing intrinsic factor. Without intrinsic factor, the body cannot absorb B12 effectively from any dietary source, including fortified foods. This condition is irreversible and requires lifelong management, typically with B12 injections, though high-dose oral supplements may also be effective for some. It is more common in women and individuals of European ancestry and tends to run in families.

Gastrointestinal Disorders and Surgery

Medical conditions affecting the stomach and intestines significantly interfere with B12 absorption. Chronic inflammatory conditions such as Crohn's disease and celiac disease can damage the lining of the small intestine, specifically the ileum where the intrinsic factor-B12 complex is absorbed. Similarly, patients who have undergone gastrointestinal surgery, such as weight-loss surgery (gastric bypass) or a partial stomach removal (gastrectomy), have a reduced capacity to produce hydrochloric acid and intrinsic factor. Small intestinal bacterial overgrowth (SIBO) can also lead to deficiency as the bacteria may consume B12 before the body has a chance to absorb it.

Medication-Induced Deficiency

Certain common medications can interfere with B12 absorption. For example, long-term use of proton pump inhibitors (PPIs) and H2-receptor antagonists, which are used to treat acid reflux and peptic ulcers, reduces stomach acid production and thus impairs the release of B12 from food proteins. The diabetes medication metformin has also been shown to reduce B12 absorption, and the risk increases with longer duration of use.

Comparison of High-Risk Groups for Vitamin B12 Deficiency


Risk Group	Primary Mechanism of Deficiency	Onset of Symptoms	Typical Treatment	Key Prevention Strategy
Older Adults	Reduced stomach acid and intrinsic factor production (often due to atrophic gastritis) leading to malabsorption of food-bound B12.	Gradual, subtle symptoms that can be mistaken for aging.	High-dose oral supplements or injections, depending on severity.	Regular screening and intake of fortified foods or supplements.
Vegans/Vegetarians	Inadequate dietary intake of animal-based B12 sources.	Can take several years for body stores to deplete.	Oral supplements or consumption of B12-fortified foods.	Consistent intake of B12 supplements or fortified foods.
Pernicious Anemia	Autoimmune destruction of cells producing intrinsic factor, leading to severe malabsorption.	Can be slow but often leads to severe deficiency over time.	Lifelong B12 injections.	Not preventable; early diagnosis and treatment are critical.
GI Surgery Patients	Surgical removal of stomach or intestinal parts disrupts acid and intrinsic factor production, limiting absorption.	Post-surgery; timing depends on extent of removal.	Lifelong supplementation, often with high-dose oral or injections.	Post-surgical B12 supplementation protocol.
Crohn's/Celiac Disease	Inflammation and damage to the intestinal lining, reducing absorption efficiency.	Variable; depends on disease severity and location.	B12 injections for severe cases; oral supplements for less severe.	Active management of the underlying disease.

Conclusion: Prioritizing Awareness and Screening

While the general population is less susceptible, certain groups are clearly at heightened risk for vitamin B12 deficiency due to a variety of factors, from diet to medical conditions. Pernicious anemia presents a uniquely challenging case, demanding lifelong management. However, malabsorption issues in older adults and dietary limitations for vegans are more widespread. Healthcare providers must prioritize screening for individuals within these high-risk groups, including patients on certain medications or those who have undergone bariatric surgery. Early diagnosis is key, as delayed treatment can lead to irreversible neurological damage. Awareness, regular monitoring, and appropriate supplementation are the most effective strategies for preventing the serious complications associated with a long-term B12 deficiency.

For more detailed information on vitamin B12, consult resources from the National Institutes of Health.(https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/)

Frequently Asked Questions

Older adults are at higher risk because the aging process can lead to reduced stomach acid production (atrophic gastritis) and less intrinsic factor, both of which are critical for absorbing vitamin B12 from food.

Yes, a vegan diet can lead to a B12 deficiency because B12 is found almost exclusively in animal products. Vegans must consciously consume fortified foods or take supplements to maintain adequate levels.

Pernicious anemia is an autoimmune disease that prevents the stomach from producing intrinsic factor, a protein needed for B12 absorption. This leads to severe malabsorption and requires lifelong treatment, often via injections.

Yes, surgical procedures like gastric bypass can drastically increase the risk of B12 deficiency. The surgery reduces the stomach's capacity to produce intrinsic factor and hydrochloric acid, which are vital for B12 absorption.

Long-term use of certain medications, including proton pump inhibitors (PPIs) for acid reflux and metformin for diabetes, can reduce the body's ability to absorb vitamin B12.

Symptoms can develop slowly and include fatigue, weakness, a sore tongue, tingling or numbness in the hands and feet, memory problems, and a decline in cognitive function.

Treatment varies depending on the cause and severity but may include vitamin B12 injections for severe cases, oral high-dose supplements, or simply increasing intake of fortified foods for those with dietary deficiencies.