A vitamin B12 deficiency, whether because you're not getting enough B12 or aren't absorbing it well, can cause symptoms like fatigue, difficulty walking, weakness, and confusion. Find out if you may be vulnerable to this condition.
13 Sneaky Causes of B12 Deficiency
Updated on Sep. 05, 2018
Vitamin B12 is one of eight B vitamins, all of which are essential to helping your body convert food into fuel. But B12 has particularly important roles in maintaining our physical and mental health, explains Julia Zumpano, RD, LD, a registered dietitian with the Cleveland Clinic Center for Human Nutrition. “It aids in the formation of red blood cells, energy production, DNA synthesis, nerve cell [functioning], and maintaining bone health,” she explains. B12 is also a key player in regulating and breaking down homocysteine, an amino acid in our blood. At elevated levels, homocysteine is linked to dementia, heart disease, stroke, and osteoporosis.
Vitamin B12 is associated with improved psychological health as well. “It can aid in reducing stress and depression,” says Zumpano. For example, she explains that B12 is crucial for a process called methylation, which helps us make mood-boosting hormones like serotonin and dopamine. 2020 research published in Cureus shows that getting sufficient vitamin B12 can even delay the onset of depression and improve the effect of anti-depressants.
Still, while it’s so important for our health and well-being, vitamin B12 isn’t just the most common B vitamin deficiency—according to 2021 research published in the Nutrition Journal, it’s the most widespread vitamin deficiency in the US alongside vitamin D.
A vegan or vegetarian diet
Vitamin B12 is primarily found in animal-based products, including liver, beef, clams, oysters, salmon, trout, tuna, eggs, milk, and yogurt, Zumpano says. 2024 research published in Dietetics research found that, on average, people following a vegan diet consume just 39% of the recommended daily intake of B12—and up to 86.5% of adult vegetarians are B12 deficient. People adhering to plant-based diets also have higher levels of homocysteines in their blood, an amino acid that B12 is responsible for regulating. In excess, this amino acid increases the risk of circulatory health problems, suggesting that a vitamin B12 deficiency could undermine the heart disease benefits of a plant-based diet.
While it’s possible to obtain vitamin B12 from fortified foods, such as nutritional yeast and some cereals, the research says that supplementation may be more effective for improving B12 status in vegetarians and vegans.
Intestinal issues
Even if you’re getting enough B12 in your diet, digestive diseases like Crohn’s or celiac disease can interfere with its absorption, says Zumpano.
“Under normal circumstances, vitamin B12 is absorbed in the intestines—as are most other nutrients,” adds Alyssa Tucci Krober, MS, RDN, CDN, a New York-based registered dietician nutritionist. “Conditions that cause inflammation and damage to the small intestines, like Crohn’s and celiac disease, can impair our ability to absorb this important vitamin.” If you’ve had surgery on your gastrointestinal tract—including bariatric or weight-loss surgery—that can reduce your body’s vitamin B12 absorption, too, Zumpano says.
Antacids
Heartburn or acid reflux doesn’t cause a vitamin B12 deficiency—but the antacids you take to combat it can block absorption. “In order for B12 to be absorbed, you need to have adequate stomach acid,” says Andrea Maxim, ND, MNLP, MCht, an Ontario-based naturopathic doctor. “Many people are taking acid blockers, which significantly reduce the amount of stomach acid you create.”
When this acid is created, the stomach releases a protein called intrinsic factor that helps the intestine absorb B12. When you reduce stomach acid with antacids, “The release of intrinsic factor becomes impaired, and therefore B12 can’t get absorbed,” says Maxim.
Prescription meds
Long-term use of some medications can lead to deficient levels, Zumpano says. Methotrexate—the frontline treatment for rheumatoid arthritis and used to treat psoriasis and some cancers—puts patients uniquely at risk for vitamin B12 deficiency, per 2024 research published in the American Journal of the Medical Sciences. Long-term use of ulcer medications (such as proton pump inhibitors), gout treatment, some antibiotics, and corticosteroids may also deplete B12 levels in the body.
Diabetes
Metformin is a widely used blood sugar-lowering medication for people with type 2 diabetes (as well as gestational diabetes and polycystic ovarian syndrome). Research published in 2023 in Cureus reports that an estimated 30% of people with type 2 diabetes using metformin long-term have low vitamin B12 levels—and 30% go on to develop vitamin B12 malabsorption issues.
Oral contraceptives
A little-known side effect of oral contraceptives is that continuous use can contribute to nutritional deficiencies, including low levels of vitamin B12, according to 2023 research published in Systematic Reviews. It’s not well-understood why, but researchers theorize that the hormones in birth control pills affect how nutrients are metabolized in your body.
Pernicious anemia
Zumpano explains that a stomach protein called intrinsic factor is required for our bodies to absorb and use vitamin B12—and so any issue with this protein’s production will lead to a B12 deficiency. Problems most commonly occur due to pernicious anemia, an autoimmune condition that causes the body to mistakenly attack the cells in the stomach that produce this intrinsic factor.
Atrophic gastritis
Atrophic gastritis is an autoimmune disease that causes your body to attack stomach lining cells, including those that produce the intrinsic factor protein required to absorb vitamin B12. According to the Cleveland Clinic, autoimmune atrophic gastritis is most commonly an inherited condition. Still, it also occurs in people with other autoimmune disorders such as thyroid diseases or type 1 diabetes.
Chronic H. pylori infection
A more common type of atrophic gastritis is called environmental metaplastic atrophic gastritis. This condition also destroys the healthy cells that make up your stomach lining, but environmental factors—not genes—trigger this condition. 2022 research published in Frontiers in Cellular and Infection Microbiology says that the main cause of atrophic gastritis is an untreated H. pylori infection, a bacteria that promotes stomach inflammation, cell damage, and microbiome changes. The Cleveland Clinic adds that age, a high-salt diet, and smoking increase the risk of developing environmental atrophic gastritis.
About half of all people have an H. pylori infection, and while it’s a common cause of other issues like stomach ulcers, many people have no symptoms. The infection can be diagnosed through several types of routine lab tests and is treated with antibiotics.
Hypothyroidism
Research published in 2019 in Medical Principles and Practice explains that atrophic gastritis affects about 40% of people with autoimmune hypothyroidism, often leading to vitamin B12 deficiency in people with the disease. Autoimmune hypothyroidism is generally caused by Hashimoto’s disease, a condition that’s largely hereditary, but environmental and lifestyle factors—such as smoking, stress, alcohol use, and vitamin D deficiency—play a significant role in triggering the disease in someone who is genetically susceptible.
Heavy alcohol use
Chronic alcohol consumption is known to interfere with the absorption of a range of vital nutrients, including proteins, healthy fats, vitamins, and minerals, per 2023 research published in Nutrients—including vitamin B12. The Cleveland Clinic explains that alcohol can damage your digestive system, killing off the stomach cells that enable your body to absorb vitamin B12.
Age
Vitamin B12 deficiency may be as high as 40% in people over 60, according to 2023 research published in the Journal of Pharmacy Practice and Research. Because our metabolic processes slow down with age, our bodies don’t absorb and use nutrients as efficiently. In addition, older people are at an increased risk for vitamin B12 deficiency because of higher incidence of conditions like pernicious anemia, long-term use of medications that interfere with B12 absorption, and insufficient dietary intake.
Stress
Is there any condition where stress doesn’t somehow make things worse? Stress exacerbates ulcers and bumps up stomach acid production (which can lead sufferers to overuse antacids). Need some ways to relax? Check out these expert tips for de-stressing in a hurry.
About the experts
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Sources
- Julia Zumpano, RD, LD, a registered dietitian with the Cleveland Clinic Center for Human Nutrition
- Alyssa Tucci, RDN, a New York-based registered dietician nutritionist
- Andrea Maxim, ND, an Ontario-based Naturopathic Doctor
- Cureus: “Vitamin B12 Supplementation: Preventing Onset and Improving Prognosis of Depression”
- Nutrition Journal: “Clinically-diagnosed vitamin deficiencies and disorders in the entire United States military population, 1997–2015”
- Dietetics: “Common Nutritional Shortcomings in Vegetarians and Vegans”
- American Journal of the Medical Sciences: “Vitamin B12 status and hyperhomocysteinemia in patients with Rheumatoid arthritis treated with methotrexate and folic acid”
- Systematic Reviews: “Prevalence of vitamin B complex deficiencies in women in reproductive age, pregnant, or lactating woman in Brazil: a systematic review and meta-analysis protocol”
- Cureus: “Metformin-Induced Vitamin B12 Deficiency in Patients With Type-2 Diabetes Mellitus”
- Cleveland Clinic: “Atrophic Gastritis”
- Frontiers in Cellular and Infection Microbiology: “Relationship between Helicobacter pylori infection and gastrointestinal microecology”
- Medical Principles and Practice: “Vitamin B12 and Vitamin D Levels in Patients with Autoimmune Hypothyroidism and Their Correlation with Anti-Thyroid Peroxidase Antibodies”
- Nutrients: “The Influence of Alcohol Consumption on Intestinal Nutrient Absorption: A Comprehensive Review”
- Cleveland Clinic: “Vitamin B12 Deficiency”
- Journal of Pharmacy Practice and Research: “Vitamin B12 deficiency in older people: a practical approach to recognition and management”
