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Vitamin B12 deficiency occurs when the body is either not getting or not absorbing enough vitamin B12, resulting in physical, neurological or psychological problems.
Vitamin B12 is a nutrient of particular concern for some older Americans because the body’s ability to absorb it may decrease with age or due to use of certain medications.[1] Estimates suggest that around 5% of individuals aged between 65 and 74 years and more than 10% of people aged 75 or older may have vitamin B12...
Vitamin B12 deficiency occurs when the body is either not getting or not absorbing enough vitamin B12, resulting in physical, neurological or psychological problems.
Vitamin B12 is a nutrient of particular concern for some older Americans because the body’s ability to absorb it may decrease with age or due to use of certain medications.[1] Estimates suggest that around 5% of individuals aged between 65 and 74 years and more than 10% of people aged 75 or older may have vitamin B12 deficiency.
In 2024 the National Institute for Health and Care Excellence (NICE), an independent U.K. organization that develops evidence-based recommendations for health care professionals, published its first guideline regarding vitamin B12 deficiency in individuals older than 16 years.[2]
About vitamin B12
Vitamin B12, also known as cobalamin, is a water-soluble nutrient that the body needs in small amounts to help with the proper functioning of the nervous system and various metabolic functions, red blood cell formation, other body cell proliferation, and energy production.[3]
Vitamin B12 is found in foods of animal origin, such as beef liver, meat, fish, dairy products and eggs (see Table, below, for examples of rich sources of this vitamin). Although plants do not naturally contain vitamin B12, some plant-based foods (such as cereals and nutritional yeasts) are fortified with this vitamin.
The bioavailability of vitamin B12 (the proportion that is absorbed, metabolized and becomes available for use by the body) varies across dietary sources. It is about three times higher in dairy products than in meats. Vitamin B12 in good dietary supplements has high bioavailability.
Although some dietary supplements contain high amounts of vitamin B12, the body absorbs only about 2% at doses of 500 micrograms (mcg) and 1.3% at doses of 1,000 mcg. Excess amounts are excreted; the vitamin is not toxic to the body.
The recommended daily allowance of vitamin B12 ranges from 0.4 mcg in healthy infants to 2.4 mcg for all nonpregnant and nonlactating healthy individuals aged 14 years or older. The recommended amount of vitamin B12 during pregnancy is 2.6 mcg and during lactation is 2.8 mcg.
Given that the body stores up to five milligrams of vitamin B12, mainly in the liver, deficiency usually does not manifest until this store is less than 300 mcg, which can take a few years.[4]
Table. Examples of Rich Food Sources of Vitamin B12[5]
| Food (Standard Portion) | Vitamin B12 (Micrograms) | Percent Daily Value |
|---|---|---|
| Beef liver, pan fried (3 ounces) | 70.7 | 2,944 |
| Clams (without shells), cooked (3 ounces) | 17 | 708 |
| Oysters, eastern, wild, cooked (3 ounces) | 14.9 | 621 |
| Nutritional yeast, fortified, from several brands (1/4 cup) | 8.3 to 24 | 346 to 1,000 |
| Salmon, Atlantic, cooked (3 ounces) | 2.6 | 108 |
| Tuna, light, canned in water (3 ounces) | 2.5 | 104 |
| Beef, ground, 85% lean, pan browned (3 ounces) | 2.4 | 100 |
| Milk, 2% milkfat (1 cup) | 1.3 | 54 |
†Brand-name combination products were excluded.
*Designated as Limited Use
**Designated as Do Not Use
***The 80-milligram dose of simvastatin is designated as Do Not Use.
Diagnosing vitamin B12 deficiency
The NICE guideline cautioned that symptoms and signs of vitamin B12 deficiency can vary between people and often overlap with those of other conditions. However, as a general rule, the guideline recommended initial testing for vitamin B12 levels in individuals who have at least one common symptom or sign and have at least one common risk factor.
The signs and symptoms include (1) abnormal blood test indicating anemia or macrocytosis (abnormally large red blood cells); (2) cognitive problems (such as difficulty concentrating or short-term memory loss); (3) visual changes suggesting problems with the optic nerve (blurred vision, optic atrophy or visual-field loss); (4) inflammation of the tongue; (5) neurological or mobility problems that cause balance issues or falls due to inability to sense movement or location usually associated with lack of coordination (ataxia), impaired gait or paresthesia (numbness or feeling of pins and needles); (6) unexplained fatigue; and (7) persistence of symptoms or signs related to anemia despite iron treatment during pregnancy or breastfeeding.
The guideline identified several risk factors for vitamin B12 deficiency. These include reversible factors, such as insufficient dietary intake (as in the case of individuals who do not consume adequate amounts of animal foods or plant-based foods or drinks fortified with the vitamin), and factors that affect absorption of the vitamin, including celiac disease, recreational use of nitrous oxide, and prolonged use of certain medications. Examples of these medications include colchicine (COLCRYS, GLOPERBA, MITIGARE and generics), metformin (GLUMETZA and generics), phenobarbital (SEZABY and generics), pregabalin (LYRICA and generics), primidone (MYSOLINE and generics), proton pump inhibitors (including omeprazole [PRILOSEC, PRILOSEC OTC and generics]) and topiramate (EPRONTIA, QUDEXY XR, TOPAMAX, TROKENDI XR and generics).
There are also irreversible (permanent) causes of vitamin B12 deficiency; however, the deficiency can be corrected effectively in these cases with lifelong replacement therapy. Examples of these irreversible causes include certain types of gastrointestinal surgery (such as removing a major portion of the stomach or the last part of the small intestine [ileum], and many bariatric operations) and autoimmune inflammation in the stomach (gastritis). Notably, autoimmune gastritis can cause a rare condition called pernicious anemia, in which the stomach lacks intrinsic factor to help with the absorption of vitamin B12 that is necessary for red blood cell maturation.
Although laboratory tests can help diagnose vitamin B12 deficiency, there is no single reliable test. For most people, the guideline recommended blood tests for either total B12 or active B12 levels as the initial diagnostic test. Although the test for active B12 tends to be more accurate (especially during pregnancy), it is more costly than the test for total B12. An expensive blood test for a biomarker called methylmalonic acid can be used for people who have an indeterminate (nondefinitive) B12 test result and symptoms or signs of deficiency. Because treatment may affect test results, the guideline recommended obtaining blood samples for testing before the initiation of B12 replacement therapy.
Vitamin B12 replacement
Treatment of vitamin B12 deficiency depends on the cause; the goal is to replace vitamin B12 and improve the symptoms and signs of deficiency. Deficiency due to suspected or confirmed dietary causes can be treated in some people with dietary changes alone.
However, the guideline also recommended oral vitamin B12 replacement therapy for people who would benefit from rapid treatment, such as people with neurological conditions, as well as intramuscular B12 injections for certain patients, including those who cannot adhere to oral replacement, have neurological conditions, are frail or have cognitive impairments.
For drug-induced vitamin B12 deficiency, the guideline recommended changing or stopping the implicated drugs if possible and using either oral or intramuscular replacement of the vitamin for as long as the person remains on the implicated drugs, as appropriate. For deficiency due to malabsorption that is irreversible, the guideline recommended lifelong intramuscular vitamin B12 replacement. However, oral replacement is possible in some other malabsorption conditions, such as celiac disease that is managed effectively by a gluten-free diet.
The guideline recommended follow-up after three months of treatment for most patients who have started replacement therapy, except during pregnancy and breastfeeding and in patients with severe symptoms, who may need an earlier evaluation. Generally, improvement in symptoms (especially severe ones) is a good indication of how well replacement therapy is working.
What You Can Do
Whenever possible, Public Citizen’s Health Research Group recommends consuming vitamin B12 from dietary sources rather than from supplements. If you have a risk factor for vitamin B12 deficiency or have any related symptoms, consult your clinician. If you decide to take an oral vitamin B12 supplement, make sure it contains at least one of the following effective types of the vitamin: cyanocobalamin, methylcobalamin or adenosylcobalamin.
References
[1] U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. https://www.dietaryguidelines.gov/sites/default/files/2021-03/Dietary_Guidelines_for_Americans_2020-2025.pdf. Accessed October 6, 2025.
[2] National Institute for Health and Care Excellence. Vitamin B12 deficiency in over 16s: diagnosis and management. March 6, 2024. www.nice.org.uk/guidance/ng239. Accessed October 6, 2025.
[3] Office of Dietary Supplements. National Institutes of Health. Vitamin B12: Fact sheet for health professionals. Updated July 2, 2025. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Accessed October 6, 2025.
[4] Marchi G, Busti F, Zidanes AL, et al. Cobalamin deficiency in the elderly. Mediterr J Hematol Infect Dis. 2020;12(1):e2020043.
[5] Office of Dietary Supplements. National Institutes of Health. Vitamin B12: Fact sheet for health professionals. Updated July 2, 2025. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Accessed October 6, 2025.
