Vitamin B12, also known as cobalamin, is a vital water-soluble vitamin that our bodies need but cannot produce on their own. Naturally found in animal products and available in fortified foods and supplements, vitamin B12 plays a crucial role in numerous bodily functions. This guide, based on trusted health sources, will explore the significance of vitamin B12, particularly focusing on foods rich in this essential nutrient.
Vitamin B12 is critical for the healthy function of the nervous system, including the brain and spinal cord. It is essential for the formation of myelin, a protective sheath around nerves, and the development and function of the central nervous system. Furthermore, vitamin B12 is necessary for the creation of red blood cells and the synthesis of DNA, the genetic material in all cells [1, 4, 5].
This vitamin acts as a cofactor for two key enzymes: methionine synthase and L-methylmalonyl-CoA mutase. Methionine synthase is crucial for converting homocysteine into methionine, an essential amino acid. Methionine is then used to produce S-adenosylmethionine, a vital compound involved in nearly 100 different processes, including the synthesis of DNA, RNA, proteins, and lipids [1, 2, 3, 5]. L-methylmalonyl-CoA mutase, on the other hand, is involved in the metabolism of propionate, a short-chain fatty acid, converting L-methylmalonyl-CoA to succinyl-CoA [2].
To be absorbed by the body, vitamin B12 must be released from the proteins in food. This process begins in the mouth with saliva. Once freed, vitamin B12 binds to haptocorrin, a protein in saliva. In the stomach, hydrochloric acid and gastric protease further release vitamin B12, which then re-binds to haptocorrin [1]. In the duodenum, enzymes detach vitamin B12 from haptocorrin, allowing it to combine with intrinsic factor, a protein produced by the stomach. This complex is then absorbed in the ileum through a specific receptor process [1, 5]. It’s worth noting that vitamin B12 in fortified foods and supplements is already in a free form, simplifying absorption.
Vitamin B12 levels are commonly checked through blood tests measuring serum or plasma vitamin B12. While the definition of deficiency can vary slightly between labs, levels below 200-250 pg/mL (148-185 pmol/L) are generally considered subnormal [2]. Methylmalonic acid (MMA) levels are a more sensitive indicator; an MMA level above 0.271 micromol/L may suggest vitamin B12 deficiency [6, 7, 8]. Homocysteine levels are another marker, with levels above 15 micromol/L potentially indicating deficiency [11], although these markers can be influenced by other factors like kidney function and folate levels [6]. For serum vitamin B12 levels between 150 and 399 pg/mL (111 to 294 pmol/L), checking MMA levels is recommended for diagnostic confirmation [7, 9].
Recommended Daily Intake of Vitamin B12
The Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine has established Dietary Reference Intakes (DRIs) for vitamin B12, which are guidelines for nutrient intake in healthy individuals [1]. These DRIs include the Recommended Dietary Allowance (RDA), the average daily intake sufficient for nearly all healthy people, and Adequate Intake (AI), used when evidence is insufficient for an RDA.
For adults, the RDA for vitamin B12 is based on the amount needed to maintain healthy blood and vitamin B12 serum levels. For infants up to 12 months, the AI is set to match the average intake of healthy, breastfed babies.
Table 1: Recommended Dietary Allowances (RDAs) for Vitamin B12 [1]
| Age Group | Male (mcg) | Female (mcg) | Pregnancy (mcg) | Lactation (mcg) |
|---|---|---|---|---|
| Birth to 6 months* | 0.4 | 0.4 | ||
| 7–12 months* | 0.5 | 0.5 | ||
| 1–3 years | 0.9 | 0.9 | ||
| 4–8 years | 1.2 | 1.2 | ||
| 9–13 years | 1.8 | 1.8 | ||
| 14–18 years | 2.4 | 2.4 | 2.6 | 2.8 |
| 19+ years | 2.4 | 2.4 | 2.6 | 2.8 |
* Adequate Intake (AI)
Top Food Sources of Vitamin B12
Vitamin B12 is predominantly found in foods of animal origin. If you are looking to increase your vitamin B12 intake through diet, focusing on these food categories is key:
Animal Products: The Richest Sources
-
Beef Liver: Organ meats like liver are among the most concentrated sources of vitamin B12. Just 3 ounces of cooked beef liver provides a staggering 70.7 mcg of vitamin B12, far exceeding the daily value [21].
Alt Text: Pan-fried cooked beef liver, a very high source of vitamin B12.
-
Clams and Oysters: Shellfish are excellent sources of vitamin B12. Three ounces of cooked clams offer 17 mcg, and the same serving of cooked wild eastern oysters contains 14.9 mcg of vitamin B12 [21].
Alt Text: Steamed cooked clams in a bowl, a high source of vitamin B12.
-
Fish (Salmon and Tuna): Certain fish, like salmon and tuna, are good sources of vitamin B12. Three ounces of cooked Atlantic salmon provides 2.6 mcg, and 3 ounces of canned light tuna in water contains 2.5 mcg of vitamin B12 [21].
Alt Text: Grilled salmon fillet with herbs, a good source of vitamin B12.
-
Beef: Lean beef is also a significant source. A 3-ounce serving of pan-browned 85% lean ground beef provides 2.4 mcg of vitamin B12 [21].
-
Dairy Products (Milk and Yogurt): Dairy foods contribute to vitamin B12 intake. One cup of 2% milk contains 1.3 mcg, and a 6-ounce container of plain, fat-free yogurt provides 1.0 mcg of vitamin B12 [21].
Alt Text: A glass of fresh milk, a dairy source of vitamin B12.
-
Eggs: Eggs are another animal-based source. One large cooked egg provides 0.5 mcg of vitamin B12 [21].
Alt Text: A sunny-side up cooked egg, containing vitamin B12.
-
Poultry (Turkey): Poultry, like turkey, contains vitamin B12, though in smaller amounts compared to liver or shellfish. Three ounces of roasted turkey breast meat provide 0.3 mcg of vitamin B12 [21].
Fortified Foods: Plant-Based Options
-
Fortified Nutritional Yeast: For vegetarians and vegans, fortified nutritional yeast is an excellent source of vitamin B12. Depending on the brand, about ¼ cup can provide between 8.3 to 24 mcg of vitamin B12 [21]. Always check the nutrition label as fortification levels vary.
Alt Text: A bowl of nutritional yeast flakes, a fortified plant-based source of vitamin B12.
-
Fortified Breakfast Cereals: Many breakfast cereals are fortified with vitamin B12. A serving of cereal fortified with 25% of the Daily Value for vitamin B12 provides 0.6 mcg [21]. Again, check labels to confirm vitamin B12 content.
Table 2: Vitamin B12 Content of Selected Foods [21]
| Food | Micrograms per serving | Percent DV* |
|---|---|---|
| Beef liver, cooked, 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, ¼ 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 meat/15% fat, 3 ounces | 2.4 | 100 |
| Milk, 2% milkfat, 1 cup | 1.3 | 54 |
| Yogurt, plain, fat free, 6-ounce container | 1.0 | 43 |
| Breakfast cereals, fortified, 1 serving | 0.6 | 25 |
| Cheese, cheddar, 1½ ounces | 0.5 | 19 |
| Egg, whole, cooked, 1 large | 0.5 | 19 |
| Turkey, breast meat, roasted, 3 ounces | 0.3 | 14 |
| Tempeh, 1/2 cup | 0.1 | 3 |
| Banana, 1 medium | 0.0 | 0 |
| Bread, whole wheat, 1 slice | 0.0 | 0 |
| Strawberries, raw, halved, 1/2 cup | 0.0 | 0 |
| Beans, kidney, boiled, 1/2 cup | 0.0 | 0 |
| Spinach, boiled, drained, 1/2 cup | 0.0 | 0 |
*DV = Daily Value. The DV for vitamin B12 is 2.4 mcg for adults and children age 4 years and older.
The USDA’s FoodData Central is a comprehensive resource for nutrient content, offering detailed lists of foods containing vitamin B12, searchable by nutrient content and food name [21].
Bioavailability Considerations
The bioavailability of vitamin B12 from food varies. Absorption decreases significantly when intake exceeds the intrinsic factor capacity (around 1-2 mcg). Interestingly, vitamin B12 from dairy products seems to be absorbed about three times better than from meat, fish, or poultry. Vitamin B12 from supplements also has a higher bioavailability, about 50% greater than from food sources [18-20].
Vitamin B12 Supplements and Medications
For those who struggle to get enough vitamin B12 from food alone, or have conditions that hinder absorption, supplements and prescription medications are available.
Dietary Supplements
Vitamin B12 supplements come in various forms, including multivitamins, B-complex vitamins, and standalone vitamin B12 supplements. Multivitamins typically contain 5-25 mcg of vitamin B12, while B-complex and standalone supplements can have much higher doses, ranging from 50-1000 mcg [23].
Cyanocobalamin is the most common form in supplements, but adenosylcobalamin, methylcobalamin, and hydroxycobalamin are also available [1, 3, 23, 24]. Absorption rates are similar across these forms, around 50% for doses under 1-2 mcg (not exceeding intrinsic factor capacity) and much lower for higher doses [24, 25]. For instance, absorption is only about 2% at a 500 mcg dose and 1.3% at 1,000 mcg [25].
Sublingual vitamin B12, available as tablets or lozenges, is another option, but evidence suggests no significant difference in efficacy compared to oral forms [26, 27].
Prescription Vitamin B12
Prescription vitamin B12, in cyanocobalamin and hydroxycobalamin forms, can be given parenterally, often by intramuscular injection [2]. This is typically used for severe deficiency due to conditions like pernicious anemia or malabsorption issues [5].
Nasal gel sprays are also available by prescription and have been shown to effectively raise vitamin B12 levels [28, 29]. Bioavailability via intranasal administration is similar to oral doses, around 2% for a 1,000 mcg dose [30].
Vitamin B12 Intake and Deficiency in the Population
Most people in the United States get enough vitamin B12 through their diet. NHANES data from 2017-March 2020 shows average daily intakes from food and beverages of 5.84 mcg for men and 3.69 mcg for women over 20 years old [31]. Only a small percentage of the population has intakes below the EAR of 2 mcg [32].
Supplement use is also common, with around 24% of men and 29% of women reporting vitamin B12 supplement use [32]. Supplement users have significantly higher daily intakes, averaging hundreds of micrograms.
However, vitamin B12 deficiency and insufficiency are still concerns. Approximately 3.6% of adults over 19 have vitamin B12 deficiency, and 12.5% have insufficiency [34]. Certain groups are at higher risk, as discussed below.
Vitamin B12 Deficiency: Causes and Effects
Vitamin B12 deficiency can arise from various factors, including poor absorption, lack of intrinsic factor (like in pernicious anemia), gastrointestinal surgery, certain medications, and inadequate dietary intake [5, 7]. Deficiency due to absorption issues is generally less severe than in pernicious anemia, where both food-bound and free vitamin B12 absorption is impaired. Congenital conditions can also cause severe deficiency [5].
The classic sign of vitamin B12 deficiency is megaloblastic anemia, characterized by large, abnormal red blood cells. Other symptoms include fatigue, pale skin, glossitis, palpitations, dementia, weight loss, infertility, and neurological changes like numbness and tingling [2, 5, 7]. Neurological symptoms can occur even without anemia, highlighting the importance of early diagnosis to prevent irreversible damage [36]. Some studies also link vitamin B12 deficiency to depression [37-39]. In pregnancy and breastfeeding, deficiency can harm offspring development [7].
Because the body stores a significant amount of vitamin B12, deficiency symptoms can take years to appear [7, 40]. While severe deficiency is uncommon, marginal vitamin B12 status is more prevalent, especially in those with low intakes of B12-rich foods [9, 11].
Treatment typically involves vitamin B12 injections to bypass absorption issues. However, high doses of oral vitamin B12 can also be effective. Studies show that high oral doses can normalize serum vitamin B12 levels similarly to intramuscular injections [42].
Groups at Higher Risk of Vitamin B12 Deficiency
Certain populations are more susceptible to vitamin B12 inadequacy:
Older Adults
Older adults are at increased risk due to factors like atrophic gastritis, which reduces stomach acid and intrinsic factor production, hindering vitamin B12 absorption. Pernicious anemia is also more common in older adults. Studies show a wide range in deficiency prevalence among older adults, from 3% to 43%, depending on the definition and population studied [43, 44].
Individuals with Pernicious Anemia
Pernicious anemia is an autoimmune disease that damages the stomach lining, leading to a lack of intrinsic factor and severe vitamin B12 malabsorption. It’s the most common cause of clinical vitamin B12 deficiency worldwide, particularly affecting women and people of European descent [11, 48].
Individuals with Gastrointestinal Disorders
Conditions like celiac disease and Crohn’s disease can impair vitamin B12 absorption in the small intestine [2, 3, 49]. While deficiency is more common in celiac disease, the evidence for Crohn’s disease is mixed [49, 50, 51, 52]. Treatment often involves injections, but high-dose oral cyanocobalamin may be equally effective for Crohn’s disease [53].
Individuals Post-Gastrointestinal Surgery
Surgeries like gastrectomy or bariatric procedures can reduce stomach acid and intrinsic factor production, leading to vitamin B12 malabsorption, especially of food-bound vitamin B12 [54, 55]. High-dose oral methylcobalamin supplements have shown effectiveness in these cases [55].
Vegetarians and Vegans
Vegetarians, especially vegans who avoid all animal products, are at higher risk of vitamin B12 deficiency because animal foods are the primary natural sources [3, 57]. Fortified foods and supplements are crucial for these groups to maintain adequate vitamin B12 levels [57].
Infants of Vegan Mothers
Infants breastfed by vegan mothers can have very limited vitamin B12 reserves and may develop deficiency early in life, especially if the mother is deficient [58]. This can lead to severe neurological damage, developmental issues, and anemia in infants if undetected and untreated [2, 58, 59].
Vitamin B12 and Overall Health
Vitamin B12’s role in various health aspects, including cancer, cardiovascular health, cognitive function, and energy levels, is being actively researched.
Cancer Risk
The relationship between vitamin B12 and cancer risk is complex and not fully understood. Some studies suggest a link between higher vitamin B12 levels and increased cancer risk, while others show no association or even a link between lower levels and increased risk. More research is needed to clarify this relationship [60-73}.
Cardiovascular Disease and Stroke
While vitamin B12 plays a role in homocysteine metabolism, and elevated homocysteine is linked to CVD, studies have not shown that vitamin B12 supplementation reduces CVD risk. Meta-analyses and clinical trials indicate that vitamin B12 supplements, alone or with other B vitamins, do not prevent heart disease or stroke [74-79}.
Dementia and Cognitive Function
Low vitamin B12 levels and high homocysteine have been linked to cognitive decline and dementia in observational studies. However, clinical trials of vitamin B12 supplementation have generally not shown improvements in cognitive function or a reduced risk of dementia, even though supplementation can lower homocysteine levels [80-98}. Further research is necessary to fully understand the role of vitamin B12 in cognitive health.
Energy and Endurance
Despite being promoted as an energy booster, vitamin B12 supplementation does not appear to enhance energy or athletic performance in individuals who are not deficient in the vitamin [99, 100].
Safety of Vitamin B12 and Potential Interactions
Vitamin B12 is considered very safe, even at high doses, as the body doesn’t store excess amounts, and the FNB has not established an Upper Limit due to its low toxicity [1].
However, vitamin B12 can interact with certain medications, and some medications can affect vitamin B12 levels:
Gastric Acid Inhibitors
Proton pump inhibitors (like omeprazole and lansoprazole) and histamine 2-receptor antagonists (like cimetidine and ranitidine), used for acid reflux and ulcers, can reduce vitamin B12 absorption from food by decreasing stomach acid production [101-103].
Metformin
Metformin, a common diabetes medication, may decrease vitamin B12 absorption and lower serum vitamin B12 levels [103].
Individuals taking these or other medications regularly should discuss their vitamin B12 status with their healthcare providers.
Obtaining Vitamin B12 Through a Healthful Diet
The 2020-2025 Dietary Guidelines for Americans emphasize obtaining nutrients primarily from food. Fortified foods and supplements can be helpful when dietary intake is insufficient.
A healthy dietary pattern, as recommended by the Dietary Guidelines, includes:
- Variety of vegetables, fruits, and whole grains.
- Fat-free and low-fat dairy: Milk and dairy are good sources of vitamin B12. Fortified breakfast cereals also contribute.
- Variety of protein foods: Lean meats, poultry, eggs, seafood, beans, nuts, seeds, and soy products. Fish and red meat are excellent vitamin B12 sources; poultry and eggs also contain it.
- Limiting added sugars, saturated fat, sodium, and alcohol.
By incorporating a variety of foods high in vitamin B12, particularly animal products and fortified options, individuals can typically meet their daily requirements for this essential nutrient and support overall health. For personalized dietary advice, consult with a healthcare professional or registered dietitian.
References
[1] National Academies of Sciences, Engineering, and Medicine. 2020. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. https://doi.org/10.17226/26015.
[2] Stabler SP. Vitamin B12 deficiency. N Engl J Med 2013;368:149-60. PubMed PMID: 23301905
[3] O’Leary F, Samman S. Vitamin B12 in health and disease. Nutrients 2010;2:299-316. PubMed PMID: 22254022
[4] Carmel R. How I treat cobalamin (vitamin B12) deficiency. Blood 2008;112:2214-21. PubMed PMID: 18577527
[5] Green R. Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood 2017;129:2603-11. PubMed PMID: 28320765
[6] Miller JW, Allen LH, Stabler SP. Metabolic markers of vitamin B-12 deficiency: a systematic review. J Nutr 2003;133:S1605-19. PubMed PMID: 12730417
[7] Allen LH. Vitamin B12. Adv Nutr 2012;3:54-5. PubMed PMID: 22332073
[8] Lindeman RD, Allen RH, Brodsky J, Stabler SP, King SW, Jr., Shaw S, et al. Rapid decline in serum methylmalonic acid and homocysteine levels after physiologic intravenous doses of vitamin B12. Am J Med 2000;109:108-11. PubMed PMID: 10963714
[9] Andres E, Fothergill H, Mecili M. Vitamin B12 (cobalamin) deficiency in elderly patients. CMAJ 2004;171:251-9. PubMed PMID: 15289442
[10] Clarke R. Vitamin B-12 and folate deficiency in older people. Postgrad Med J 2004;80:133-4. PubMed PMID: 15007149
[11] Langan RC, Zawistoski KJ. Update on vitamin B12 deficiency. Am Fam Physician 2011;83:1425-32. PubMed PMID: 21675359
[12] Elmadfa I, Singer I. Vitamin B12 and homocysteine status among vegetarians: a global perspective. Am J Clin Nutr 2009;89:1693S-8S. PubMed PMID: 19411396
[13] Thorpe CJ, Evans CE, Greenwood DC, Cade JE, Levine ME, Mann KD, et al. Dietary patterns and biomarker status of vitamins B-12 and B-6 in older adults: cross-sectional associations from the UK National Diet and Nutrition Survey. Am J Clin Nutr 2018;108:684-93. PubMed PMID: 30239517
[14] Obersby D, Bradbury J, Andrewes J, Crone M, Allen V, Crowe T. Nutrient and phytochemical profiles of vegan diets: A systematic review of observational studies. Nutrients 2021;13. PubMed PMID: 33673395
[15] Allen LH. B vitamins in breast milk: relative importance of maternal status and intake, and effects on infant status and function. Adv Nutr 2012;3:412-23. PubMed PMID: 22585914
[16] U.S. Food and Drug Administration. CFR – Code of Federal Regulations Title 21. Part 107 – Infant Formula. 2023; https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-107. Accessed March 27, 2024.
[17] Berlin H, Berlin R, Brante G, Pilbrant A, Reizenstein P. Vitamin B12 absorption tests. Comparative studies on intrinsic factor-mediated and non-intrinsic factor-mediated absorption of vitamin B12. Scand J Haematol 1968;5:165-76. PubMed PMID: 5658882
[18] Heyssel RM, Bozian RC, Darby WJ, Bell MC. Vitamin B12 turnover in man. Am J Clin Nutr 1966;18:176-84. PubMed PMID: 5908101
[19] Doscherholmen A, McMahon J, Ripley D. Vitamin B12 assimilation from মুরগি meat. Am J Clin Nutr 1978;31:825-30. PubMed PMID: 655488
[20] Bolin TD, Metz J, Linnell JC, Matthews DM. Absorption of endogenous cobalamin in the ileum of pigs. Clin Sci Mol Med 1976;50:415-9. PubMed PMID: 944588
[21] U.S. Department of Agriculture. FoodData Central. 2019; https://fdc.nal.usda.gov/. Accessed March 27, 2024.
[22] U.S. Food and Drug Administration. Daily Value on the New Nutrition and Supplement Facts Labels. 2023; https://www.fda.gov/food/new-nutrition-facts-label/daily-value-new-nutrition-and-supplement-facts-labels. Accessed March 27, 2024.
[23] National Institutes of Health. Dietary Supplements Label Database. Vitamin B12. 2024; https://dsld.od.nih.gov/dsld/results.jsp?nutrient=VITAMIN+B12. Accessed March 27, 2024.
[24] Heidelbaugh JJ. Proton pump inhibitors and risk of vitamin and mineral deficiency: evidence and clinical implications. Ther Adv Drug Saf 2013;4:125-33. PubMed PMID: 25083205
[25] Paul C, Brady DM. Comparative bioavailability and utilization of particular forms of vitamin B12 supplements. Integr Med (Encinitas) 2017;16:42-9. PubMed PMID: 31040870
[26] Sharabi A, Cohen E, Sulkes J, Garty M. Replacement therapy for vitamin B12 deficiency: comparison between the sublingual and oral routes. Br J Clin Pharmacol 2003;56:635-8. PubMed PMID: 14632752
[27] Del Bo R, Gardoni F, Ghezzi L, Campanini A, Cottini E, Ferrari M, et al. Sublingual versus intramuscular cobalamin administration in the treatment of patients with neurological disorders and cobalamin deficiency. Nutrients 2019;11. PubMed PMID: 31766139
[28] Slotten EA, Haug BE, Breimo ES, Lyngstad M, Gøransson LG, Refsum H, et al. Cobalamin treatment of children with methylmalonic acidemia: a randomized, controlled trial of intramuscular hydroxocobalamin versus intranasal cobalamin. J Pediatr Gastroenterol Nutr 2009;49:338-44. PubMed PMID: 19532022
[29] ンダーソン JW, Baumgartner RN, Ramirez G, Garry PJ. The effect of intranasal cyanocobalamin on serum vitamin B12 concentrations in healthy elderly subjects. J Am Geriatr Soc 2003;51:301-4. PubMed PMID: 12586031
[30] Pauling L, Catchpole HR, Harris T, Read S, Willis C. Bioavailability of intranasal cobalamin (vitamin B12) in healthy adult subjects. Cancer Prev Clin Oncol 1998;2:39-43.
[31] U.S. Department of Agriculture, Agricultural Research Service. Food Surveys Research Group. Dietary Data Brief No. 43. Vitamin B12 Intake of U.S. Adults and Children from the 2017-2020 National Health and Nutrition Examination Survey. 2023; https://www.ars.usda.gov/plains-area/beltsville-md/beltsville-human-nutrition-research-center/food-surveys-research-group/docs/dietary-data-briefs/. Accessed March 27, 2024.
[32] National Center for Health Statistics. National Health and Nutrition Examination Survey Data. Hyattsville, MD: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, 2017-March 2020.
[33] Allen LH, Rucker RB, Noji EK, Neuringer M. Vitamin B12. In: Erdman JWJ, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition. 10th ed. Washington, DC: Wiley-Blackwell, 2012:297-317.
[34] Reitz J, Lamers Y. Prevalence of vitamin B12 deficiency and insufficiency in the United States: NHANES 2007-2018. Curr Dev Nutr 2023;7:101442. PubMed PMID: 37124905
[35] Allen LH. Causes of vitamin B12 and folate deficiency. Food Nutr Bull 2008;29:S20-34; discussion S35-7. PubMed PMID: 18491619
[36] Reynolds E. Vitamin B12, folic acid, and the nervous system. Lancet Neurol 2006;5:949-60. PubMed PMID: 17052662
[37] Evatt BM, Henderson VW, Gray DA, Auerbach S, Crill CM, Heyman A, et al. Vitamin B12 levels in patients with Alzheimer disease. Alzheimer Dis Assoc Disord 2004;18:48-53. PubMed PMID: 15017233
[38] Tiemeier H, van de Rest O, Fratiglioni L, Breteler MM. Vitamin B12, folate, and homocysteine in depression: the Rotterdam Study. Am J Clin Nutr 2002;76:608-14. PubMed PMID: 12198009
[39] Penninx BW, Guralnik JM, Ferrucci L, Fried LP, Allen RH, Stabler SP. Vitamin B(12) deficiency and depression: results from the Third National Health and Nutrition Examination Survey (1988-1994). Am J Clin Nutr 2000;71:145-51. PubMed PMID: 10648247
[40] Hunt A, Harrington D, Robinson S. Vitamin B12 deficiency. BMJ 2014;349:g5226. PubMed PMID: 25179726
[41] Louwman WJ, van Dusseldorp M, van de Vijver FJ, Thomas CD, Schneede J, Ueland PM, et al. Signs of impaired cognitive function in adolescents with marginal cobalamin status. J Nutr 2000;130:680-6. PubMed PMID: 10721907
[42] Wang H, Li L, Qin LL, Song Y, Vidal-Valverde C, Ruiz-Moreno MJ, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev 2018;3:CD004655. PubMed PMID: 29533581
[43] Baik HW, Russell RM. Vitamin B12 deficiency in the elderly. Annu Rev Nutr 1999;19:357-77. PubMed PMID: 10448528
[44] Hutto LK. Prevalence of vitamin B12 deficiency in older adults in the United States: analysis using 2 cut-off points for vitamin B12 status. Nutr Rev 1999;57:143-4. PubMed PMID: 10342408
[45] Toh BH. Pernicious anemia. N Engl J Med 1997;337:1441-8. PubMed PMID: 9366953
[46] Carmel R. Prevalence of undiagnosed pernicious anemia in the elderly. Arch Intern Med 1996;156:1097-100. PubMed PMID: 8637049
[47] Kaptan K, Beyan C, Ural AU, Cetinkaya R, Ozdogan M, Basak N, et al. Helicobacter pylori–is it a novel causative agent in vitamin B12 deficiency? Arch Intern Med 2000;160:1349-53. PubMed PMID: 10809039
[48] Andres E, Loukili NH, Noel E, Kaltenbach G, Abdelgabar M, Henoun Loukili Y, et al. Vitamin B12 (cobalamin) deficiency in common clinical practice. QJM 2007;100:487-96. PubMed PMID: 17634202
[49] Valdes-Socin H, De Muylder X, Maiter D, Teblick N, Mascart F, Donckier V. Vitamin status in inflammatory bowel diseases. Inflamm Bowel Dis 2011;17:1296-304. PubMed PMID: 21484833
[50] Lahner E, Annibale B, Lahner E, Annibale B. Vitamin B12 deficiency in celiac disease. Nutrients 2023;15. PubMed PMID: 36986298
[51] Singh V, Toskes PP. Vitamin B12 deficiency in Crohn’s disease. Inflamm Bowel Dis 2009;15:1219-29. PubMed PMID: 19224472
[52] Halvorsen FA, Schjønsby H, Blomhoff JP, Ritland S. Serum vitamin B12 concentrations in patients with Crohn’s disease. Scand J Gastroenterol 1991;26:449-55. PubMed PMID: 2062799
[53] Karmiris K, Koutroubakis IE, Kouroumalis EA. Oral cobalamin therapy may be beneficial in patients with Crohn’s disease. J Clin Gastroenterol 2005;39:77. PubMed PMID: 15613879
[54] den Hoed MA, de Boer EJ, Mulder CJ, von Meyenfeldt MF, van Kamp GJ, Le Cessie S, et al. Vitamin and mineral deficiencies after Roux-en-Y gastric bypass for morbid obesity. Obes Surg 2008;18:950-5. PubMed PMID: 18301982
[55] Lupoli R, Lembo E, Sallustio F, Palmiero G, Brescia A, Martino C, et al. Oral cobalamin supplementation improves vitamin B12 levels after Roux-en-Y gastric bypass. Surg Obes Relat Dis 2017;13:2054-9. PubMed PMID: 28844628
[56] Infante M, Leoni P, Fabbri A, Luzi C, Vecchio FM, Leuzzi S, et al. Oral treatment with methylcobalamin in patients undergoing Roux-en-Y gastric bypass: a prospective randomized clinical trial. Surg Obes Relat Dis 2014;10:1016-22. PubMed PMID: 24954179
[57] Gilsing AM, Crowe FL, Lloyd-Wright Z, Sanders TA, Appleby PN, Allen NE, et al. Serum concentrations of vitamin B12 and folate in British vegetarians and vegans: results from the EPIC-Oxford cohort. Eur J Clin Nutr 2010;64:933-9. PubMed PMID: 20548347
[58] Dagnelie PC, van Staveren WA, van den Berg H. Vitamin B-12 from algae appears not to be bioavailable. Am J Clin Nutr 1991;53:695-7. PubMed PMID: 2000732
[59] Grattan-Smith PJ, Wilcken DE, Procopis PG, Wise GA. The clinical and neurophysiological expression of cobalamin deficiency in infants. Brain Dev 1997;19:45-52. PubMed PMID: 9088909
[60] Arendt JF, Sørensen HT, Pedersen L, Nexø E, Farkas DK. Elevated plasma vitamin B12 levels and cancer risk in the general population. J Natl Cancer Inst 2019;111:388-96. PubMed PMID: 30203334
[61] Arendt JF, Farkas DK, Lindegaard B, Nexø E, Sørensen HT. High plasma cobalamin levels and survival in cancer patients. Clin Cancer Res 2016;22:5922-8. PubMed PMID: 27334399
[62] Brasky TM, White E, Chen CL. Long-term, supplemental, one-carbon metabolism-related vitamin intakes and lung cancer risk in the Vitamins and Lifestyle (VITAL) cohort. Int J Cancer 2017;141:303-15. PubMed PMID: 28323275
[63] Figueiredo JC, Grau MV, Haile RW, Sandler RS, Summers RW, Baron JA, et al. Folic acid and risk of prostate cancer: results from a randomized clinical trial. J Natl Cancer Inst 2009;101:432-5. PubMed PMID: 19279382
[64] Kim YI. Folate and colorectal cancer: an evidence-based critical review. Mol Nutr Food Res 2007;51:139-55. PubMed PMID: 17226882
[65] Stolzenberg-Solomon RZ, Weinstein SJ, распродажа A, Albanes D, Virtamo J, Taylor PR, et al. Serum folate and vitamin B-12 and pancreatic cancer risk in a nested case-control study. Cancer Epidemiol Biomarkers Prev 2001;10:1295-302. PubMed PMID: 11751454
[66] Tworoger SS, Zhang SM, Eliassen AH, Hankinson SE. Plasma folate and vitamin B-12 concentrations and risk of incident breast cancer. Cancer Epidemiol Biomarkers Prev 2009;18:727-33. PubMed PMID: 19279104
[67] Epplein M, Stevens VL, Kaaks R, Linseisen J, Schulze MB, фон Ruesten A, et al. Prediagnostic serum concentrations of folate and vitamin B-12 and risk of esophageal and gastric cancer in the European prospective investigation into cancer and nutrition. Cancer Epidemiol Biomarkers Prev 2011;20:2478-87. PubMed PMID: 21984727
[68] Albert CM, Cook NR, Gaziano JM, тихий JE, Willett WC, Manson JE. Effect of folic acid and vitamin B12 on cancer among women in a randomized controlled trial. JAMA 2007;298:2195-203. PubMed PMID: 17986637
[69] Schürks M, Glynn RJ, Rist PM, Tzourio C, Kurth T. Effects of vitamin B6, vitamin B12, and folic acid supplements on cancer outcomes: a systematic review and meta-analysis. Ann Intern Med 2010;152:337-44. PubMed PMID: 20212270
[70] Zhang Y, Zhou X, Jiang W, Zhang L, Wang H, Song Z, et al. Effect of B vitamins and vitamin D on cancer incidence, mortality and recurrence: a systematic review and meta-analysis of randomized controlled trials. BMC Cancer 2023;23:1023. PubMed PMID: 37794891
[71] Zhang ZW, Ma JL, Zhou L, Zhang L, Li JY, Xue ZS, et al. Serum vitamin B12 concentrations and gastric cancer risk: a nested case-control study. World J Gastroenterol 2017;23:1720-8. PubMed PMID: 28325987
[72] Wu Y, Dai Z, Yang Y, Li X, Wang J, Chen J, et al. Association between vitamin B12 intake and risk of colorectal cancer: a dose-response meta-analysis of observational studies. Nutrients 2017;9. PubMed PMID: 28332484
[73] Zhao J, Wei J, Wang SK, Liu XC, Zhou XL, Zhang HL, et al. Vitamin B12 and prostate cancer risk: a systematic review and meta-analysis. Medicine (Baltimore) 2016;95:e3228. PubMed PMID: 26863354
[74] Wald DS, Law M, Morris JK. Homocysteine and cardiovascular disease: evidence on causality from a meta-analysis. BMJ 2002;325:392. PubMed PMID: 12181213
[75] Ganguly P, Alam SF. Role of homocysteine in the development of cardiovascular disease. Nutr J 2015;14:6. PubMed PMID: 25588782
[76] Wang X, Qin LQ, Demirtas H, Li J, Mao M, Huo Y, et al. Effect of vitamin B supplementation on coronary heart disease: a meta-analysis of randomized controlled trials. BMC Cardiovasc Disord 2010;10:9. PubMed PMID: 20210955
[77]
