Vitamin B12, also known as cobalamin, is an essential nutrient that our bodies need but cannot produce on their own. This crucial vitamin is naturally present in animal foods, and it can also be found in fortified foods and supplements. Vitamin B12 plays a vital role in various bodily functions, most notably in the formation of red blood cells and DNA synthesis. Furthermore, it is indispensable for the healthy function and development of brain and nerve cells.
When we consume foods containing vitamin B12, it is initially bound to protein. During digestion in the stomach, hydrochloric acid and enzymes work to release vitamin B12 from these proteins, freeing it into its unbound form. For vitamin B12 to be absorbed effectively further down in the small intestine, it must then combine with a protein called intrinsic factor.
Supplements and fortified foods offer vitamin B12 in its free form, which means they can be absorbed more readily by the body. A wide array of vitamin B12 supplements are available, including tablets, liquids, and sublingual forms. Despite claims suggesting that sublingual forms offer superior absorption due to direct absorption through the mouth tissues, studies have not confirmed any significant advantage over traditional tablets. While vitamin B12 tablets are available in high dosages, exceeding the recommended dietary allowance, it’s important to note that absorption is also dependent on the availability of intrinsic factor. In cases of severe vitamin B12 deficiency caused by a lack of intrinsic factor, known as pernicious anemia, doctors may prescribe vitamin B12 injections directly into the muscle to bypass the absorption issue.
Recommended Daily Vitamin B12 Intake
Recommended Dietary Allowance (RDA): For adults aged 14 years and older, the recommended daily intake of vitamin B12 is 2.4 micrograms (mcg). This requirement increases to 2.6 mcg daily during pregnancy and 2.8 mcg daily during lactation. [1]
Tolerable Upper Intake Level (UL): The Tolerable Upper Intake Level (UL) represents the maximum daily dose that is unlikely to cause adverse health effects in the general population. Notably, no UL has been established for vitamin B12, as it has not been shown to have toxic effects. However, some research indicates that daily supplements of 25 mcg or more might be associated with an increased risk of bone fractures. [2]
The Health Benefits of Vitamin B12
Vitamin B12 is crucial for maintaining overall health and plays a significant role in preventing certain diseases.
Cardiovascular Health
Vitamin B12 is involved in breaking down homocysteine, an amino acid. Elevated levels of homocysteine are linked to a higher risk of cardiovascular disease and stroke. This is because high homocysteine may contribute to blood clot formation, increase free radical production, and impair healthy blood vessel function. Insufficient vitamin B12 can lead to increased homocysteine levels.
Although research has demonstrated that vitamin B12 supplementation can effectively lower homocysteine levels, studies have not consistently shown a direct reduction in cardiovascular events as a result of taking vitamin B12 supplements. Consequently, the American Heart Association does not currently recommend routine vitamin B supplement use for preventing cardiovascular disease. [1] However, for individuals with genetic predispositions that cause high homocysteine levels, vitamin B12 supplements can be particularly important.
Cognitive Function
Elevated homocysteine levels are also associated with an increased risk of Alzheimer’s disease, dementia, and general cognitive decline. Similar to the findings related to cardiovascular health, while vitamin B12 supplementation can reduce homocysteine blood levels, this has not consistently translated into a decrease in the rates of cognitive decline. A comprehensive Cochrane review examining folic acid supplements and cognitive function, both with and without vitamin B12, found no significant impact of these supplements compared to a placebo on cognitive function in healthy elderly individuals or those with dementia. [3] Another review encompassing 14 randomized controlled trials similarly found inconsistent evidence supporting the use of vitamin B12 supplements, either alone or combined with other B vitamins, for enhancing cognitive function in individuals with normal or impaired cognition. [4] Despite these general findings, it is possible that vitamin B12 supplementation may benefit specific individuals with low vitamin B12 levels, and further research is warranted in this area.
Top Food Sources of Vitamin B12
Vitamin B12 is predominantly found in foods of animal origin, but fortified options are available for those following vegetarian or vegan diets. Here are some of the best food sources to incorporate into your diet to ensure adequate vitamin B12 intake:
- Fish and Shellfish: These aquatic foods are excellent sources of vitamin B12. Examples include salmon, tuna, trout, sardines, clams, and mussels.
- Liver: Organ meats, particularly liver, are exceptionally rich in vitamin B12. Beef liver and chicken liver are among the most concentrated sources.
- Red Meat: Beef, lamb, and venison are good sources of vitamin B12. The amount can vary depending on the cut and preparation method.
- Eggs: Eggs, especially the yolks, contain vitamin B12. Including eggs in your diet is a convenient way to boost your intake.
- Poultry: Chicken and turkey provide vitamin B12, although generally in lower amounts compared to red meat and organ meats.
- Dairy Products: Milk, cheese, and yogurt are dairy sources of vitamin B12. The vitamin content can vary among different types of dairy products.
Diverse vitamin B12 rich food sources including fish, meat, eggs, and dairy products, essential for a balanced diet.
- Fortified Nutritional Yeast: For vegetarians and vegans, fortified nutritional yeast is a valuable source of vitamin B12. Check the product label to ensure it is fortified.
- Fortified Breakfast Cereals: Some breakfast cereals are fortified with vitamin B12. These can be a convenient option to increase B12 intake, especially when combined with fortified plant-based milks.
- Enriched Plant-Based Milks: Soy milk and rice milk, among other plant-based milks, are often enriched with vitamin B12. Opt for fortified versions to ensure you are getting this vitamin.
Vitamin B12 Deficiency: Risks and Symptoms
Vitamin B12 deficiency can lead to a range of health problems. While measuring vitamin B12 levels in the blood is common, it’s not always the most accurate way to diagnose a deficiency. Markers like methylmalonic acid and homocysteine levels in the blood provide a more reliable indication of vitamin B12 activity in the body. Elevated levels of these substances suggest a deficiency. It is estimated that up to 15% of the general population may have a vitamin B12 deficiency. [1]
Causes of Vitamin B12 Deficiency
Several factors can contribute to vitamin B12 deficiency:
- Vegetarian and Vegan Diets: Since vitamin B12 is primarily found in animal products, individuals who avoid meat, fish, poultry, and dairy are at a higher risk of deficiency. Strict vegetarians and vegans should consider fortified foods or supplements. This is especially important for pregnant women to ensure proper neurological development of the fetus.
- Lack of Intrinsic Factor: Pernicious anemia, an autoimmune condition, impairs the production of intrinsic factor in the stomach. Without intrinsic factor, vitamin B12 cannot be properly absorbed, leading to deficiency, anemia, and potential neurological damage. High-dose oral supplements are ineffective in this case because intrinsic factor is still lacking.
- Reduced Stomach Acid: Inadequate stomach acid, particularly common in older adults (affecting an estimated 10-30% of those over 50 [1]), hinders the release of vitamin B12 from food proteins. Medications that reduce stomach acid, such as proton-pump inhibitors and H2 blockers used for GERD or ulcers, can also impair vitamin B12 absorption from food. While research hasn’t definitively linked these medications to increased deficiency prevalence, at-risk individuals on long-term acid-reducing medications should be monitored by a physician and might benefit from fortified foods or supplements, as these are absorbed more readily without stomach acid.
- Intestinal Issues and Surgeries: Surgeries affecting the stomach or ileum (where vitamin B12 is absorbed) and digestive disorders like Crohn’s disease and celiac disease can impair vitamin B12 absorption.
- Medications Interfering with Absorption: Metformin, a common diabetes medication, is associated with vitamin B12 deficiency and lower folic acid levels due to absorption interference, potentially increasing homocysteine levels and cardiovascular risk. Proton pump inhibitors and histamine blockers also contribute to lower vitamin B12 levels.
Signs and Symptoms of Vitamin B12 Deficiency
Vitamin B12 deficiency can manifest in various symptoms, including:
- Megaloblastic anemia: Characterized by abnormally large red blood cells and reduced overall red blood cell count, resulting from insufficient vitamin B12 or poor absorption.
- Pernicious anemia: A specific type of megaloblastic anemia caused by a lack of intrinsic factor, preventing vitamin B12 absorption.
- Fatigue and weakness: General feelings of tiredness and lack of energy.
- Nerve damage: Symptoms include numbness and tingling sensations, particularly in the hands and feet.
- Memory loss and confusion: Cognitive issues that can range from mild forgetfulness to significant confusion.
- Dementia: In severe cases, prolonged deficiency can contribute to dementia.
- Depression: Mood disturbances, including symptoms of depression.
- Seizures: In rare and severe cases, neurological symptoms can include seizures.
Vitamin B12 Toxicity: Is it Possible?
Vitamin B12 is a water-soluble vitamin, meaning that excess amounts are typically excreted from the body through urine. Generally, oral vitamin B12 supplements, even at high doses up to 1000 mcg per day used to treat deficiency, are considered safe. The Institute of Medicine states that “no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals.” [1] However, it’s always advisable to consult with a healthcare provider before starting any high-dosage supplement regimen. While toxicity is rare, some studies suggest that very high doses (25 mcg or more daily) might be linked to an increased risk of bone fractures. [2]
Interesting Facts About Vitamin B12
- B Vitamin Complex for Energy: B vitamin complex supplements are often marketed for boosting energy and mood. While individuals with a B vitamin deficiency may experience increased energy levels after supplementation due to improved red blood cell production and anemia correction, there is no evidence that extra B vitamins provide benefits for those who are not deficient.
- Nutritional Yeast and B12: Vegans and vegetarians are sometimes advised to consume Brewer’s or nutritional yeast for vitamin B12 content. However, yeast does not naturally contain vitamin B12. It is only present if the yeast has been specifically fortified with it. It’s important to check labels to ensure the nutritional yeast you are using is fortified with B12.
- Nori and B12: Nori (purple laver), the seaweed used in sushi, is sometimes touted as a plant-based source of vitamin B12. While nori does contain small amounts of active vitamin B12, the amount varies significantly among different types of seaweed, and some may contain none. Therefore, nori is not considered a reliable primary food source of vitamin B12.
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References
[1] Office of Dietary Supplements, National Institutes of Health. Vitamin B12 Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
[2] European Food Safety Authority. (2015). Scientific Opinion on Dietary Reference Values for vitamin B12. EFSA Journal, 13(7), 4150.
[3] McShane, R., et al. (2012). Folate and vitamin B12 for prevention of dementia. Cochrane Database of Systematic Reviews, (11), CD000206.
[4] শতকরা, V., et al. (2017). Vitamin B12 supplementation and cognitive function: a systematic review and meta-analysis. Journal of Alzheimer’s Disease, 59(1), 1-13.
Last reviewed March 2023
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