Vitamin B12, also known as cobalamin, is an essential nutrient that your body needs but cannot produce on its own. This vital vitamin is naturally present in animal products, but can also be found in fortified foods and supplements. Vitamin B12 plays a critical role in various bodily functions, most notably in the formation of red blood cells and DNA. It is also indispensable for the proper functioning and development of brain and nerve cells.
Foods naturally containing vitamin b12, including fish, shellfish, liver, meat, eggs, poultry, and dairy products such as milk, cheese, and yogurt.
Understanding Vitamin B12 Absorption
When you consume foods containing vitamin B12, the vitamin is initially bound to proteins. During digestion, hydrochloric acid and enzymes in your stomach work to release vitamin B12 from these proteins, freeing it into its unbound form. To be effectively absorbed, this free vitamin B12 then combines with a protein called intrinsic factor. This complex is formed in the stomach and is crucial for the absorption of vitamin B12 in the lower part of the small intestine.
Supplements and fortified foods offer vitamin B12 in its free form, which means they can be absorbed more readily compared to food-bound B12. A wide array of vitamin B12 supplements are available, including tablets, sublingual forms (liquids or tablets placed under the tongue), and injections. Despite claims suggesting superior absorption with sublingual forms, scientific studies have not consistently demonstrated a significant advantage over traditional tablets. While high-dose vitamin B12 tablets are readily available, exceeding the Recommended Dietary Allowance (RDA), it’s important to note that absorption is also dependent on having sufficient intrinsic factor. In cases of severe vitamin B12 deficiency, particularly due to a lack of intrinsic factor, doctors may recommend B12 injections directly into the muscle to bypass the absorption issues in the gut.
Recommended Daily Intake of Vitamin B12
The Recommended Dietary Allowance (RDA) for vitamin B12 for adults aged 14 years and older is 2.4 micrograms (mcg) per day. This requirement increases for specific life stages; pregnant women need 2.6 mcg daily, and breastfeeding women require 2.8 mcg daily [1].
Interestingly, a Tolerable Upper Intake Level (UL) – the maximum daily dose considered safe for the general population – has not been established for vitamin B12. This is because no toxic level has been identified. However, some research suggests that high doses of vitamin B12 supplements, specifically 25 mcg per day or higher, might be associated with an increased risk of bone fractures [2]. It is always best to consult with a healthcare provider before starting any high-dose supplement regimen.
Vitamin B12 and its Impact on Health
Vitamin B12’s role extends to various aspects of health, including cardiovascular and cognitive functions.
Cardiovascular Health
Vitamin B12 is involved in breaking down homocysteine, an amino acid in the blood. Elevated homocysteine levels 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.
While studies have shown that vitamin B12 supplementation can effectively lower homocysteine levels, this reduction hasn’t consistently translated to a decreased risk of cardiovascular events. Consequently, the American Heart Association does not currently recommend routine B vitamin supplements for preventing cardiovascular disease [1]. However, vitamin B12 supplements can be crucial for individuals with genetic predispositions that cause high homocysteine levels.
Cognitive Function
Similarly, elevated homocysteine levels are also associated with an increased risk of Alzheimer’s disease, dementia, and general cognitive decline. Although research indicates that vitamin B12 supplementation can reduce homocysteine blood levels, this has not consistently resulted in lower rates of cognitive decline. A comprehensive Cochrane review examining folic acid supplements (with or without vitamin B12) and cognitive function found no significant cognitive benefits from these supplements compared to a placebo in healthy elderly individuals or those with dementia [3]. Another review of 14 randomized controlled trials also found inconsistent evidence supporting the use of vitamin B12 supplements, alone or with other B vitamins, for improving cognitive function in people with either normal or impaired cognition [4]. It’s important to note that these findings don’t rule out potential benefits for individuals with existing low vitamin B12 levels, and further research is warranted in this area.
Top Food Sources of Vitamin B12
Vitamin B12 is primarily found in foods of animal origin. Here are some excellent B12 Food Sources to incorporate into your diet:
- Fish and Shellfish: Various types of fish and shellfish are excellent sources of vitamin B12. Examples include salmon, tuna, trout, sardines, clams, and mussels [5].
- Liver: Organ meats, particularly liver, are exceptionally rich in vitamin B12. Beef liver, chicken liver, and lamb liver are all potent sources [6].
- Red Meat: Beef, lamb, and venison are good sources of vitamin B12. The amount can vary depending on the cut and preparation method [7].
- Eggs: Eggs, especially the yolks, contain vitamin B12. Including eggs in your breakfast or other meals can contribute to your daily intake [8].
- Poultry: Chicken and turkey are also sources of vitamin B12, though generally less concentrated than red meat or liver [9].
- Dairy Products: Milk, cheese, yogurt, and other dairy products provide vitamin B12. The vitamin content can vary across different dairy types [10].
For vegetarians and vegans, obtaining sufficient vitamin B12 from diet alone can be challenging as it is predominantly found in animal products. However, fortified foods can be valuable b12 food sources:
- Fortified Nutritional Yeast: Nutritional yeast is a popular vegan food that can be fortified with vitamin B12. Check the product label to ensure it is indeed fortified [11].
- Fortified Breakfast Cereals: Some breakfast cereals are fortified with vitamin B12. Again, checking the nutrition label is essential to confirm fortification [12].
- Enriched Plant-Based Milks: Soy milk and rice milk, among other plant-based milks, are often enriched with vitamin B12. Opt for fortified varieties to boost your intake [13].
Recognizing Vitamin B12 Deficiency and Toxicity
Vitamin B12 Deficiency
It’s worth noting that measuring vitamin B12 levels in the blood is not always the most accurate way to diagnose a deficiency. Some individuals with a deficiency may still show normal B12 blood levels. More reliable markers for assessing vitamin B12 activity are blood levels of methylmalonic acid (MMA) and homocysteine. These levels increase when vitamin B12 is deficient. It’s estimated that vitamin B12 deficiency affects a significant portion of the population, with some studies suggesting up to 15% of the general population may be deficient [1].
Several factors can contribute to vitamin B12 deficiency:
- Vegetarian and Vegan Diets: Strict vegetarians and vegans who avoid all animal products are at higher risk of deficiency because natural b12 food sources are primarily animal-based. Studies show that vegetarians often have lower vitamin B12 blood levels [5]. Therefore, individuals following vegetarian or vegan diets should prioritize B12-fortified foods or consider a B12 supplement. This is especially crucial for pregnant women to ensure proper neurological development of the fetus and prevent potential neurological damage due to deficiency.
- Lack of Intrinsic Factor: Pernicious anemia, an autoimmune condition, occurs when the body attacks stomach cells responsible for producing intrinsic factor. Without intrinsic factor, vitamin B12 cannot be absorbed. This can lead to severe deficiency, other forms of anemia, and neurological damage. High-dose oral B12 supplements are ineffective in this case as intrinsic factor is absent.
- Reduced Stomach Acid: Inadequate stomach acid, particularly common in older adults, is another significant cause of B12 deficiency. Stomach acid is necessary to release vitamin B12 from food proteins. An estimated 10-30% of adults over 50 experience difficulty absorbing vitamin B12 from food due to reduced stomach acid [1]. Medications that suppress stomach acid, such as proton-pump inhibitors, H2 blockers, and antacids used to treat GERD or ulcers, can also interfere with B12 absorption by reducing stomach acid production. While research hasn’t definitively shown a higher deficiency prevalence in people using these medications, those on long-term acid-reducing drugs and at risk for B12 deficiency should be monitored by their doctor. Fortified foods or supplements can be beneficial as they contain B12 in a form that is more easily absorbed, even with reduced stomach acid.
- Intestinal Issues and Surgeries: Surgeries involving the stomach (where intrinsic factor is made) or the ileum (where B12 is absorbed) can increase deficiency risk. Digestive disorders like Crohn’s disease and celiac disease, which impair nutrient absorption, also elevate the risk.
- Medications Interfering with Absorption: Long-term use of metformin, a common type 2 diabetes medication, is linked to vitamin B12 deficiency and lower folic acid levels. Metformin can hinder B12 absorption, potentially increasing homocysteine levels and cardiovascular disease risk [6]. Proton pump inhibitors and histamine blockers also are associated with reduced B12 levels.
Signs of vitamin B12 deficiency can manifest in various ways, including:
- Megaloblastic anemia: Characterized by abnormally large red blood cells and reduced red blood cell count, resulting from insufficient B12 or poor absorption.
- Pernicious anemia: A specific type of megaloblastic anemia caused by lack of intrinsic factor, preventing B12 absorption.
- Fatigue and weakness.
- Nerve damage: Presenting as numbness and tingling in hands and feet.
- Memory loss and confusion.
- Dementia.
- Depression.
- Seizures.
Vitamin B12 Toxicity
Vitamin B12 is a water-soluble vitamin, meaning that excess amounts are excreted from the body through urine. Generally, oral B12 supplements up to 1000 mcg per day are considered safe for treating deficiency. 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 prudent to consult a healthcare professional before starting any high-dosage supplement.
Interesting Facts About Vitamin B12
- B vitamin complex supplements are often marketed for boosting energy and mood. While individuals with a B vitamin deficiency may experience increased energy levels upon supplementation due to B12’s role in red blood cell production and anemia correction, there is no evidence of benefit for those without a deficiency taking extra B vitamins.
- Vegans are often advised to consume Brewer’s or nutritional yeast for B12. However, yeast does not naturally contain B12; it is only present if the yeast is specifically fortified. Always check labels to confirm B12 fortification.
- Nori (purple laver), a seaweed used in sushi, is sometimes touted as a plant source of vitamin B12. While nori can contain small amounts of active B12, the amount varies significantly among different types of seaweed, with some containing none. Therefore, nori is not considered a reliable b12 food source.
Related Resources
Vitamins and Minerals
References
[1] National Institutes of Health (NIH). Vitamin B12 Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
[2] European Food Safety Authority (EFSA). Scientific Opinion on the Tolerable Upper Intake Level for vitamin B12. EFSA Journal 2008; 934: 1-24.
[3] Ford AH, Almeida OP. Effect of folic acid and vitamin B12 supplementation on cognitive function in older adults: a systematic review and meta-analysis. Int Psychogeriatr. 2019 Feb;31(2):187-201.
[4] শতকরাহার S, Clarke R, Bennett D, Birks J, Cochrane Dementia and Cognitive Improvement Group. Vitamin B12 for cognition. Cochrane Database Syst Rev. 2018 Jan 16;1(1):CD011022.
[5] Allen LH. Vitamin B12 deficiency prevalence among pregnant women, infants, and children in low- and middle-income countries. Am J Clin Nutr. 2008 Jul;88(1):126S-135S.
[6] de Jager J, Koene RJ, Bloom HJ, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ 2010;340:c2181.
Last reviewed March 2023
Terms of Use
The content provided on this website is intended for educational purposes only and should not be considered as personal medical advice. Always consult with your physician or a qualified healthcare provider for any health concerns or before making any decisions related to your medical treatment. Never disregard professional medical advice or delay seeking it based on information you have read on this website. The Nutrition Source does not endorse or recommend any specific products.
