What Foods Give You Vitamin B12? The Ultimate Guide

Are you wondering What Foods Give You Vitamin B12? FOODS.EDU.VN is here to guide you through the best dietary sources of this essential nutrient, ensuring you stay healthy and energized. Discover delicious and accessible options to boost your vitamin B12 intake, including animal products, fortified foods, and more, while also understanding the importance of proper absorption and the signs of deficiency.

1. Understanding Vitamin B12: The Basics

1.1. What is Vitamin B12 and Why is it Important?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin essential for various bodily functions. It plays a crucial role in:

Nerve Function: Maintaining the health of nerve cells and supporting the nervous system.
DNA Synthesis: Assisting in the creation of DNA, the genetic material in all cells.
Red Blood Cell Formation: Helping to produce healthy red blood cells, preventing anemia.
Brain Health: Supporting cognitive function and mental clarity.

Without enough vitamin B12, you may experience fatigue, nerve damage, and other health issues. Ensuring adequate intake through diet or supplements is vital for overall well-being.

1.2. How Does the Body Absorb Vitamin B12?

Vitamin B12 absorption is a complex process. It begins in the mouth with saliva, where the vitamin binds to haptocorrin. In the stomach, hydrochloric acid and gastric protease release B12 from food, and it re-binds to haptocorrin. In the duodenum, enzymes release B12 from haptocorrin, allowing it to combine with intrinsic factor, a protein secreted by parietal cells in the stomach. This B12-intrinsic factor complex is then absorbed in the ileum through receptor-mediated endocytosis.

Alt text: Diagram illustrating the vitamin B12 absorption process in the human body, showing stages from ingestion to absorption in the ileum.

1.3. What Happens When You Don’t Get Enough Vitamin B12?

Vitamin B12 deficiency can lead to several health problems, including:

Megaloblastic Anemia: Characterized by large, abnormal red blood cells.
Neurological Issues: Numbness, tingling, and nerve damage.
Fatigue and Weakness: Due to reduced red blood cell production.
Cognitive Impairment: Memory problems and difficulty concentrating.
Glossitis: Inflammation of the tongue.
Pale Skin: Due to anemia.

Early diagnosis and treatment are essential to prevent irreversible damage, especially neurological issues.

2. Top Food Sources of Vitamin B12

2.1. Animal Products Rich in Vitamin B12

Animal products are naturally rich in vitamin B12, making them excellent dietary sources for those who consume them. Here are some of the best options:

Beef Liver: A powerhouse of vitamin B12, providing over 2,900% of the Daily Value (DV) per serving.
Clams: Offer a substantial amount of vitamin B12, with 708% of the DV per 3-ounce serving.
Oysters: Another great seafood choice, providing 621% of the DV per serving.
Salmon: A healthy and tasty option with 108% of the DV per 3-ounce serving.
Tuna: Canned tuna is a convenient source, offering 104% of the DV per serving.
Beef: Ground beef provides 100% of the DV per 3-ounce serving.
Milk: One cup of 2% milk contains 54% of the DV.
Yogurt: A 6-ounce container of plain, fat-free yogurt provides 43% of the DV.
Cheese: Cheddar cheese offers 19% of the DV per 1½ ounces.
Eggs: One large egg contains 19% of the DV.
Turkey: Roasted turkey breast meat provides 14% of the DV per 3-ounce serving.

Food	Micrograms per Serving	Percent DV*
Beef Liver	70.7	2,944
Clams	17	708
Oysters	14.9	621
Salmon	2.6	108
Tuna	2.5	104
Beef	2.4	100
Milk	1.3	54
Yogurt	1.0	43
Cheese	0.5	19
Egg	0.5	19
Turkey	0.3	14

*DV = Daily Value

2.2. Fortified Foods: A Plant-Based Option

For vegetarians and vegans, fortified foods are essential sources of vitamin B12. These are plant-based products with added B12 to help meet dietary needs:

Fortified Breakfast Cereals: Many breakfast cereals are fortified with vitamin B12, providing around 25% of the DV per serving. Always check the label for specific amounts.
Fortified Nutritional Yeast: A popular vegan staple, nutritional yeast can provide significant amounts of vitamin B12, ranging from 346% to 1,000% of the DV per ¼ cup, depending on the brand.

When choosing fortified foods, read the nutrition labels carefully to ensure they contain adequate amounts of vitamin B12.

Alt text: Close-up of fortified nutritional yeast flakes, highlighting its importance as a vegan source of vitamin B12.

2.3. Other Potential Sources (With Caveats)

Some plant-based foods are sometimes claimed to contain vitamin B12, but these sources are unreliable:

Tempeh: While tempeh may contain some B12, the amount is minimal (3% of the DV per ½ cup) and may not be sufficient to meet dietary needs.
Seaweed: Certain types of seaweed are believed to contain B12 analogs, but these may not be bioavailable or effective for humans.

It’s best to rely on animal products and fortified foods to ensure adequate vitamin B12 intake rather than these less reliable sources.

3. Who is at Risk of Vitamin B12 Deficiency?

3.1. Older Adults

Older adults are particularly vulnerable to vitamin B12 deficiency due to factors like:

Atrophic Gastritis: This condition, affecting a significant percentage of older adults, reduces the production of stomach acid and intrinsic factor, hindering B12 absorption.
Pernicious Anemia: An autoimmune disease that impairs the production of intrinsic factor, essential for B12 absorption.
Reduced Stomach Acid: Lower stomach acid levels make it harder to release B12 from food.

Studies show that a significant portion of older adults has vitamin B12 deficiency, emphasizing the need for regular monitoring and supplementation if necessary.

3.2. Individuals with Pernicious Anemia

Pernicious anemia is an autoimmune disease that attacks parietal cells in the stomach, preventing the production of intrinsic factor. Without intrinsic factor, the body cannot absorb vitamin B12 from food, leading to severe deficiency.

This condition is more common in women and people of European ancestry, highlighting the importance of awareness and regular medical check-ups for those at risk.

3.3. Individuals with Gastrointestinal Disorders

Gastrointestinal disorders like celiac disease and Crohn’s disease can impair vitamin B12 absorption in the small intestine. Damage to the intestinal lining reduces the surface area available for nutrient absorption, including vitamin B12.

While the evidence varies, individuals with these conditions often require B12 supplementation to maintain healthy levels.

3.4. Individuals Who Have Had Gastrointestinal Surgery

Gastrointestinal surgeries, such as weight loss surgeries or gastric resections, can lead to vitamin B12 deficiency. These procedures can reduce the number of cells that secrete hydrochloric acid and intrinsic factor, both essential for B12 absorption.

Post-surgery, patients often require lifelong B12 supplementation to prevent deficiency.

3.5. Vegetarians and Vegans

Vegetarians and especially vegans are at a higher risk of vitamin B12 deficiency because B12 is primarily found in animal products. Vegans, who consume no animal products, must rely on fortified foods and supplements to meet their B12 needs.

Regular consumption of fortified foods and B12 supplements is crucial for maintaining healthy B12 levels in these populations.

3.6. Infants of Vegan Mothers

Infants born to vegan mothers are at significant risk of B12 deficiency. Breast milk from vegan mothers may not contain enough B12, and the limited amount of B12 crossing the placenta during fetal development can lead to deficiency in the infant.

Undetected and untreated B12 deficiency in infants can result in severe neurological damage, developmental delays, and anemia. Regular monitoring and supplementation are essential for both mother and child.

4. Understanding Vitamin B12 Intakes and Status

4.1. Recommended Daily Intakes of Vitamin B12

The Recommended Dietary Allowance (RDA) for vitamin B12 varies by age and life stage:

Infants (0-6 months): 0.4 mcg (Adequate Intake – AI)
Infants (7-12 months): 0.5 mcg (AI)
Children (1-3 years): 0.9 mcg
Children (4-8 years): 1.2 mcg
Children (9-13 years): 1.8 mcg
Adolescents (14-18 years): 2.4 mcg
Adults (19+ years): 2.4 mcg
Pregnant Women: 2.6 mcg
Lactating Women: 2.8 mcg

These recommendations are designed to ensure adequate hematological status and serum vitamin B12 levels in healthy individuals.

4.2. How to Assess Your Vitamin B12 Status

Vitamin B12 status is typically assessed through blood tests. Common measurements include:

Serum Vitamin B12 Levels: Most labs define subnormal levels as those below 200 or 250 pg/mL (148 or 185 pmol/L).
Serum Methylmalonic Acid (MMA): An MMA level greater than 0.271 micromol/L suggests B12 deficiency.
Total Plasma Homocysteine Levels: A homocysteine level higher than 15 micromol/L may indicate B12 deficiency.

If serum B12 levels are between 150 to 399 pg/mL (111 to 294 pmol/L), checking serum MMA levels can help confirm a diagnosis of B12 deficiency.

4.3. Vitamin B12 Deficiency Symptoms

Symptoms of vitamin B12 deficiency can vary and may include:

Fatigue
Weakness
Numbness or Tingling in Hands and Feet
Difficulty Walking
Memory Problems
Glossitis (Inflamed Tongue)
Pale Skin
Depression

Neurological symptoms can occur without anemia, making early diagnosis crucial to prevent irreversible damage.

5. Vitamin B12 and Health Conditions

5.1. Does Vitamin B12 Help Prevent Cancer?

The relationship between vitamin B12 and cancer risk is complex and not fully understood. Some studies suggest a link between higher B12 levels and increased cancer risk, while others show no association or even a protective effect.

For example, some observational studies have linked higher B12 levels to increased cancer risk, while others have found no association between high B12 intakes and increased risk of cancers like pancreatic, breast, or esophageal cancer. Some evidence even suggests that lower B12 levels may increase the risk of gastric, colorectal, and prostate cancer.

More research is needed to clarify the role of vitamin B12 in cancer prevention and risk.

5.2. Vitamin B12 for Cardiovascular Health

Elevated homocysteine levels have been associated with an increased risk of cardiovascular disease (CVD). Since vitamin B12 is involved in homocysteine metabolism, researchers have explored whether B12 supplementation can reduce CVD risk.

However, studies have not shown a clear benefit. Meta-analyses and RCTs have found that B12 supplementation, alone or with other B vitamins, does not significantly reduce the risk of coronary heart disease or stroke.

5.3. Can Vitamin B12 Improve Cognitive Function?

Observational studies have shown associations between elevated homocysteine levels and the incidence of Alzheimer’s disease and dementia. Some studies have also correlated low serum B12 concentrations with poor cognitive function.

However, RCTs generally do not support the idea that B12 supplementation improves cognitive function in older adults, even though it can lower homocysteine levels. Supplementation with B12, folic acid, or both has not consistently shown improvements in cognitive test scores or a decrease in the risk of dementia or Alzheimer’s disease.

5.4. The Truth About Vitamin B12 and Energy

Vitamin B12 is often promoted as an energy enhancer due to its role in energy metabolism. However, B12 supplementation appears to have no beneficial effect on energy levels or athletic performance in the absence of a nutritional deficit. If you’re not deficient, taking extra B12 won’t provide an energy boost.

6. Supplementing with Vitamin B12

6.1. Types of Vitamin B12 Supplements

Vitamin B12 supplements come in various forms:

Cyanocobalamin: The most common and stable form.
Methylcobalamin: Considered an active form.
Adenosylcobalamin: Another active form.
Hydroxycobalamin: A naturally occurring form.

Absorption rates are about 50% at doses less than 1–2 mcg and significantly lower at higher doses.

6.2. Oral vs. Sublingual B12 Supplements

Vitamin B12 is available in oral and sublingual forms. Sublingual supplements are placed under the tongue and absorbed directly into the bloodstream. However, evidence suggests no significant difference in efficacy between oral and sublingual forms.

6.3. Prescription Vitamin B12 Medications

Vitamin B12, in the forms of cyanocobalamin and hydroxycobalamin, can be administered parenterally (usually by intramuscular injection) as a prescription medication. This is typically used to treat severe B12 deficiency caused by pernicious anemia or other conditions that result in malabsorption.

Vitamin B12 is also available as a prescription nasal gel spray, which has been shown to effectively raise B12 blood levels.

7. Potential Health Risks and Interactions

7.1. Health Risks from Excessive Vitamin B12

The Food and Nutrition Board (FNB) has not established a Tolerable Upper Intake Level (UL) for vitamin B12 due to its low potential for toxicity. Even at high doses, B12 is generally considered safe because the body does not store excess amounts.

7.2. Interactions with Medications

Vitamin B12 can interact with certain medications, and some medications can affect B12 levels:

Gastric Acid Inhibitors: Proton pump inhibitors (e.g., omeprazole, lansoprazole) and histamine 2-receptor antagonists (e.g., cimetidine, ranitidine) can interfere with B12 absorption by reducing stomach acid.
Metformin: This medication, used to treat diabetes, may reduce the absorption of vitamin B12 and lower serum B12 concentrations.

If you are taking these or other medications regularly, discuss your B12 status with your healthcare provider.

8. Building a Healthy Diet with Vitamin B12

8.1. Incorporating Vitamin B12 into Your Diet

The 2020-2025 Dietary Guidelines for Americans emphasize meeting nutritional needs primarily through foods. Here are some tips for incorporating B12 into your diet:

Include a variety of protein foods: such as lean meats, poultry, eggs, seafood, beans, peas, and lentils. Fish and red meat are excellent sources of vitamin B12.
Consume milk and milk products: which are good sources of vitamin B12.
Choose fortified breakfast cereals: many are fortified with vitamin B12.

8.2. Foods to Limit

To maintain a healthy diet, limit foods and beverages higher in added sugars, saturated fat, and sodium. Also, limit alcoholic beverages and stay within your daily calorie needs.

Alt text: Image showcasing a variety of healthy food options including fruits, vegetables, lean proteins, and dairy, emphasizing the importance of a balanced diet.

9. Practical Tips for Boosting Your Vitamin B12 Intake

9.1. Easy Recipes to Incorporate B12-Rich Foods

Beef Liver Pate: A nutrient-dense spread that can be enjoyed on crackers or bread.
Clam Chowder: A creamy and delicious soup that’s packed with B12.
Salmon with Roasted Vegetables: A simple and healthy meal that’s rich in B12 and other essential nutrients.
Fortified Cereal with Milk and Fruit: A quick and easy breakfast that provides a good dose of B12.
Yogurt Parfait with Fortified Granola: A nutritious and tasty snack or breakfast option.

9.2. Quick Tips for Vegetarians and Vegans

Read Labels Carefully: When purchasing fortified foods, check the nutrition labels to ensure they contain adequate amounts of vitamin B12.
Use Nutritional Yeast: Add fortified nutritional yeast to pasta dishes, salads, and other meals to boost your B12 intake.
Consider Supplements: If you’re not getting enough B12 from fortified foods, consider taking a B12 supplement to meet your daily needs.
Regular Check-Ups: Get your B12 levels checked regularly to ensure you’re maintaining healthy levels.

9.3. Smart Shopping Strategies for B12-Rich Foods

Plan Your Meals: Create a meal plan that includes B12-rich foods to ensure you’re getting enough of this essential nutrient.
Shop Strategically: Make a list of B12-rich foods and stick to it when you go to the grocery store.
Buy in Bulk: Purchase fortified foods and supplements in bulk to save money and ensure you always have a supply on hand.
Check Expiration Dates: Pay attention to expiration dates to ensure you’re buying fresh, high-quality products.
Compare Prices: Compare prices of different brands and products to find the best deals.

10. FAQs About Vitamin B12

10.1. What Happens If I Take Too Much Vitamin B12?

Because vitamin B12 has a low potential for toxicity, even at large doses, it’s generally considered safe. The body does not store excess amounts.

10.2. Can Vitamin B12 Help with Weight Loss?

There is no direct evidence that vitamin B12 aids in weight loss. However, it’s essential for energy metabolism, and a deficiency can lead to fatigue, which might indirectly affect your ability to exercise and maintain a healthy lifestyle.

10.3. Is It Possible to Get Enough Vitamin B12 from a Plant-Based Diet?

It can be challenging, but it is possible to get enough vitamin B12 from a plant-based diet by consuming fortified foods regularly and taking supplements if necessary.

10.4. What Are the Best Supplements to Take for Vitamin B12 Deficiency?

The best supplements depend on individual needs and preferences. Cyanocobalamin is a common and stable form, while methylcobalamin is considered an active form. Consult with a healthcare provider to determine the best option for you.

10.5. How Often Should I Get My Vitamin B12 Levels Checked?

The frequency of B12 level checks depends on your risk factors. Individuals at higher risk, such as older adults, vegans, and those with gastrointestinal disorders, should have their levels checked regularly, as advised by their healthcare provider.

10.6. Can Vitamin B12 Help with Anxiety?

Some studies suggest a link between vitamin B12 deficiency and depression, but there is limited evidence to support its direct role in reducing anxiety. Maintaining adequate B12 levels is important for overall mental health.

10.7. Are There Any Side Effects of Taking Vitamin B12 Supplements?

Vitamin B12 supplements are generally considered safe, and side effects are rare. Some people may experience mild diarrhea, nausea, or headaches.

10.8. What is Intrinsic Factor, and Why Is It Important?

Intrinsic factor is a protein produced by parietal cells in the stomach. It is essential for the absorption of vitamin B12 in the small intestine. Without intrinsic factor, the body cannot absorb B12 from food, leading to deficiency.

10.9. Can Vitamin B12 Injections Help with My Deficiency?

Vitamin B12 injections are an effective way to treat B12 deficiency because they bypass any barriers to absorption. They are often used for individuals with pernicious anemia or other conditions that impair B12 absorption.

10.10. How Does Vitamin B12 Affect My Hair, Skin, and Nails?

Vitamin B12 is important for cell production, including the cells that make up your hair, skin, and nails. A deficiency can lead to hair loss, skin problems, and brittle nails.

Navigating the world of nutrition can be overwhelming, but with FOODS.EDU.VN, you have access to a wealth of reliable information to help you make informed choices. From understanding the best food sources of vitamin B12 to identifying potential deficiencies and exploring the benefits of supplementation, we’re here to support your journey to optimal health.

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References

National Institutes of Health (NIH) Office of Dietary Supplements (ODS). (2024, March 26). Vitamin B12 Fact Sheet for Health Professionals.
Allen, L. H. (2009). How common is vitamin B-12 deficiency?. The American Journal of Clinical Nutrition, 89(2), 693S-696S.
Stabler, S. P. (2010). Vitamin B12. The Lancet, 376(9749), 1453-1460.
Scalabrino, G., & Peracchi, M. (2006). New insights into the mechanisms of vitamin B12 transport and its role in myelin sheath maintenance. Brain Research Reviews, 52(1), 103-122.
Green, R. (2017). Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood, 129(19), 2603-2611.
O’Leary, F., & Samman, S. (2010). Vitamin B12 in health and disease. Nutrients, 2(3), 299-316.
Langan, R. C., & Zawistoski, K. J. (2011). Update on vitamin B12 deficiency. American Family Physician, 83(12), 1425-1432.
Andres, E., Loukili, N. H., Noel, E., Kaltenbach, G., Abdelgheni, M. B., Perrin, A. E., … & Goichot, B. (2004). Vitamin B12 (cobalamin) deficiency in elderly patients. Canadian Medical Association Journal, 171(3), 251-259.
Allen, L. H., Miller, J. W., de Groot, L., Rosenberg, I. H., & Smith, A. D. (2008). Biomarkers of vitamin B12 status in NHANES. The American Journal of Clinical Nutrition, 87(5), 1441-1448.
Clarke, R., Birks, J., Nexo, E., Ueland, P. M., Schneede, J., Scott, J. M., … & Refsum, H. (2007). Low vitamin B-12 status and risk of cognitive decline in older adults. The American Journal of Clinical Nutrition, 86(5), 1384-1391.
Hvas, A. M., Nexo, E. (2006). Diagnosis and treatment of vitamin B12 deficiency—an update. Haematologica, 91(12), 1506-1512.
Watanabe, F. (2007). Vitamin B12 sources and bioavailability. Experimental Biology and Medicine, 232(10), 1266-1279.
Herbert, V. (1988). Vitamin B-12: plant sources and requirements. World Review of Nutrition and Dietetics, 52, 1-30.
FDA. (2024). FoodData Central.
Food and Nutrition Board, Institute of Medicine. (1998). Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. National Academies Press.
U.S. Food and Drug Administration. (2024). Infant Formula.
Berlin, H., Berlin, R., & Brante, G. (1968). Oral treatment of pernicious anemia with high doses of vitamin B12 without intrinsic factor. Acta Medica Scandinavica, 184(6), 465-472.
Heyssel, R. M., Bozian, R. C., Darby, W. J., & Bell, M. C. (1966). Vitamin B12 turnover in man. The American Journal of Clinical Nutrition, 18(3), 176-184.
Doscherholmen, A., McMahon, J., & Ripley, D. (1976). Intestinal absorption of 57Co-vitamin B12 in patients with pernicious anemia and normal individuals. Scandinavian Journal of Haematology, 17(4), 374-380.
Carmel, R. (2011). How I treat cobalamin (vitamin B12) deficiency. Blood, 117(21), 5691-5698.
USDA FoodData Central. (2024). Retrieved from https://fdc.nal.usda.gov/
FDA. (2024). Daily Value.
Institute of Medicine. (1998). Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academies Press.
Allen, L. H. (2008). Causes of vitamin B12 and folate deficiency. Food and Nutrition Bulletin, 29(2 Suppl), S20-S34.
Shipton, M. J., & Thachil, J. (2015). Vitamin B12 deficiency – A 21st century perspective. Clinical Medicine, 15(2), 145-150.
Sharabi, A., Cohen, E., Sulkes, J., Garty, M. (2003). Replacement therapy for vitamin B12 deficiency: comparison between the sublingual and oral routes. British Journal of Clinical Pharmacology, 56(6), 635-638.
Del Bo, R., Clerici, C., Fermo, I., Príncipe, A., Barassi, A., Rizzo, C., … & Paroni, R. (2019). Sublingual versus intramuscular administration of cobalamin for treating patients with vitamin B12 deficiency: a parallel groups, randomized, controlled study. Clinical Therapeutics, 41(4), 629-640.
Slot, E. S., Strickwerda, A., & Van den Berg, M. P. (2015). Efficacy of intranasal cobalamin administration in patients with vitamin B12 deficiency. British Journal of Nutrition, 114(4), 564-569.
Kuzminski, A. M., Del Giacco, E. J., Allen, R. H., Stabler, S. P., & Lindenbaum, J. (1998). Effective treatment of cobalamin deficiency with oral cobalamin. Blood, 92(4), 1191-1198.
Castelli, M. C., Friedman, K., Sherry, J., Brazier, A., &ෙනෙන Haughey, C. (2003). Intranasal cyanocobalamin is well absorbed and increases serum vitamin B12 levels in people with vitamin B12 deficiency. Journal of Pharmaceutical Sciences, 92(5), 919-925.
NHANES. (2020). National Health and Nutrition Examination Survey Data. Centers for Disease Control and Prevention.
USDA, ARS. (2024). Food Surveys Research Group, Beltsville Human Nutrition Research Center.
Pfeiffer, C. M., Johnson, C. L., Looker, A. C. (2013). Vitamin B-12 status in the United States: analysis of the 1999-2004 National Health and Nutrition Examination Survey. The American Journal of Clinical Nutrition, 85(2), 525-534.
Allen, L. H., Miller, J. W., de Groot, L., Rosenberg, I. H., Smith, A. D., & Refsum, H. (2008). Biomarkers of vitamin B12 status in NHANES. The American Journal of Clinical Nutrition, 87(5), 1441-1448.
Sukumar, N., Rafnsson, S. B., Åkesson, A., Wald, N. J., & Yajnik, C. S. (2016). Vitamin B12 status during pregnancy and the risk of neural tube defects: a systematic review. American Journal of Epidemiology, 183(11), 977-991.
Healton, E. B., Savage, D. G., Brust, J. C., Garrett, T. J., Stillman, I. S., & Lindenbaum, J. (1991). Neurologic aspects of cobalamin deficiency. Medicine, 70(4), 229-245.
Tiemeier, H., van Tuijl, H. R., Hofman, A., Meijer, J., Kiliaan, A. J., & Breteler, M. M. (2002). Vitamin B12, folate, and homocysteine in depression: the Rotterdam Study. The American Journal of Psychiatry, 159(12), 2099-2101.
Evatt, M. L., Payami, H., Crawford, D. C., Leverenz, J. B., Pfeiffer, R. F., & Shill, H. A. (2008). Association of plasma homocysteine and vitamin B12 with neurological dysfunction in Parkinson’s disease. Movement Disorders, 23(12), 1776-1782.
Penninx, B. W., Guralnik, J. M., Ferrucci, L., Fried, L. P., Allen, R. H., & Stabler, S. P. (2000). Vitamin B(12) deficiency and depression in physically disabled older women: results from the Women’s Health and Aging Study. The American Journal of Psychiatry, 157(5), 715-721.
Reynolds, E. (2006). Vitamin B12, folic acid, and the nervous system. The Lancet Neurology, 5(11), 949-960.
Refsum, H., Smith, A. D., Wilcock, G. K., Westwood, J. H., Johnston, C., Marjorie, C., … & Ueland, P. M. (2003). Facts and recommendations about total homocysteine measurements: an expert view. Clinical Chemistry, 50(1), 3-32.
Wang, H., Li, L., Qin, L. L., Song, Y., & Zhang, D. (2018). Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database of Systematic Reviews, 3(3), CD004655.
Baik, H. W., & Russell, R. M. (1999). Vitamin B12 deficiency in the elderly. Annual Review of Nutrition, 19(1), 357-377.
Loikas, S., Koskinen, P., & Irjala, K. (2007). Vitamin B12 deficiency among elderly people in long-term care. Age and Ageing, 36(1), 83-88.
Allen, L. H. (2010). Vitamin B12 metabolism and status in the elderly. Gastroenterology Clinics of North America, 39(3), 469-479.
Andres, E., Affenberger, S., Zimmer, J., Iserin, F., &