Introduction
Vitamin B12, a vital water-soluble vitamin, plays a pivotal role in numerous bodily functions, making it indispensable for overall well-being. Naturally occurring in certain foods, fortified in others, and available as supplements and prescription medications, vitamin B12 is crucial for maintaining optimal health. Scientifically known as cobalamins due to the presence of cobalt, vitamin B12 encompasses compounds like methylcobalamin and 5-deoxyadenosylcobalamin, the metabolically active forms, alongside hydroxycobalamin and cyanocobalamin, which convert into active forms within the body [1]. Understanding the significance of vitamin B12 and identifying foods high in B12 is paramount for individuals seeking to ensure they meet their nutritional needs and prevent deficiency.
Vitamin B12 is fundamental for several key processes, including the healthy development, myelination, and function of the central nervous system. It is also essential for the formation of healthy red blood cells and DNA synthesis [1, 4, 5]. This vitamin acts as a crucial cofactor for two enzymes: methionine synthase and L-methylmalonyl-CoA mutase [1, 2, 3, 5]. Methionine synthase is responsible for converting homocysteine into methionine, an essential amino acid [1, 2]. Methionine is then needed to produce S-adenosylmethionine, a universal methyl donor vital for nearly 100 different substrates, including DNA, RNA, proteins, and lipids [3, 5]. Meanwhile, L-methylmalonyl-CoA mutase plays a role in the metabolism of propionate, a short-chain fatty acid, by converting L-methylmalonyl-CoA to succinyl-CoA [2].
The absorption of vitamin B12 from foods high in B12 is a complex process. Initially bound to protein in food, vitamin B12 must be released to be absorbed effectively [5]. 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 from food, where it again binds to haptocorrin [1]. In the duodenum, digestive enzymes liberate vitamin B12 from haptocorrin, allowing it to combine with intrinsic factor, a protein secreted by parietal cells in the stomach. This complex is then absorbed in the distal ileum through receptor-mediated endocytosis [1, 5]. In contrast, vitamin B12 added to fortified foods high in B12 and dietary supplements is already in free form, bypassing the initial separation step.
Assessing vitamin B12 status typically involves measuring serum or plasma vitamin B12 levels. While the threshold for deficiency varies, levels below 200 or 250 pg/mL (148 or 185 pmol/L) are generally considered subnormal [2]. Serum methylmalonic acid (MMA) levels are a more sensitive indicator; an MMA level above 0.271 micromol/L suggests deficiency [6, 7, 8]. Elevated total plasma homocysteine levels, above 15 micromol/L, can also indicate vitamin B12 deficiency [11], although this marker is less specific [6]. Experts recommend checking serum MMA levels if vitamin B12 levels are between 150 to 399 pg/mL (111 to 294 pmol/L) to confirm a diagnosis of deficiency [7, 9].
Recommended Daily Intake of Vitamin B12
The Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine provides Dietary Reference Intakes (DRIs) for vitamin B12 and other essential nutrients [1]. DRIs are a set of reference values used for planning and assessing nutrient intakes for healthy populations, varying by age and sex. These include:
- Recommended Dietary Allowance (RDA): The average daily intake level sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals, primarily used for planning adequate diets for individuals.
- Adequate Intake (AI): Established when evidence is insufficient to set an RDA, this level is assumed to ensure nutritional adequacy.
- Estimated Average Requirement (EAR): The average daily intake level estimated to meet the needs of 50% of healthy individuals, used to assess group intakes and plan diets for groups.
- Tolerable Upper Intake Level (UL): The maximum daily intake unlikely to cause adverse health effects.
Table 1 outlines the current RDAs for vitamin B12 [1]. For adults, the RDA is based on the amount needed to maintain healthy hematological status and serum vitamin B12 levels. For infants up to 12 months, an AI is set, equivalent to the mean vitamin B12 intake of healthy, breastfed infants.
Table 1: Recommended Dietary Allowances (RDAs) for Vitamin B12 [1]
| Age | Male | Female | Pregnancy | Lactation |
|---|---|---|---|---|
| Birth to 6 months* | 0.4 mcg | 0.4 mcg | ||
| 7–12 months* | 0.5 mcg | 0.5 mcg | ||
| 1–3 years | 0.9 mcg | 0.9 mcg | ||
| 4–8 years | 1.2 mcg | 1.2 mcg | ||
| 9–13 years | 1.8 mcg | 1.8 mcg | ||
| 14–18 years | 2.4 mcg | 2.4 mcg | 2.6 mcg | 2.8 mcg |
| 19+ years | 2.4 mcg | 2.4 mcg | 2.6 mcg | 2.8 mcg |
*Adequate Intake (AI)
Top Food Sources of Vitamin B12
Vitamin B12 is predominantly found in foods high in B12 of animal origin. These include a variety of options that can be incorporated into a balanced diet.
Animal-Based Foods High in B12
- Meat and Poultry: Beef, lamb, and poultry are excellent sources of vitamin B12. Red meat, particularly liver, is exceptionally high in B12. Even lean meats contribute significantly to daily intake.
- Fish and Seafood: Fish such as salmon, tuna, and trout, as well as shellfish like clams and oysters, are rich in vitamin B12. These options not only provide B12 but also beneficial omega-3 fatty acids.
- Dairy Products: Milk, cheese, yogurt, and other dairy products are good sources of vitamin B12. Dairy is a convenient way for many to consume B12 regularly.
- Eggs: Eggs, particularly the yolks, contain vitamin B12. They are a versatile and accessible source of this vitamin.
Image alt text: Pan-fried beef liver, a top food high in vitamin B12, presented on a plate to highlight its rich nutrient content.
While plant-based foods do not naturally contain vitamin B12, there are fortified options available, making it possible for vegetarians and vegans to meet their B12 needs through diet.
Fortified Plant-Based Foods High in B12
- Fortified Breakfast Cereals: Many breakfast cereals are fortified with vitamin B12, offering a readily available source, especially for those who do not consume animal products.
- Fortified Nutritional Yeast: Nutritional yeast, particularly fortified varieties, is a significant plant-based source of vitamin B12. It has a cheesy flavor and can be added to various dishes.
- Fortified Plant-Based Milks and Yogurts: Some plant-based milk alternatives (soy, almond, oat milk) and yogurts are fortified with vitamin B12. Checking labels is important to confirm fortification levels.
The bioavailability of vitamin B12 from foods high in B12 varies. Absorption decreases significantly when the intrinsic factor’s capacity is exceeded, typically at doses around 1–2 mcg [17]. Bioavailability also differs among food sources. For instance, vitamin B12 from dairy products appears to be absorbed about three times more efficiently than from meat, fish, and poultry. Supplements tend to have about 50% higher bioavailability compared to food sources [18, 19, 20].
Table 2 provides a detailed list of foods high in B12 and their vitamin B12 content per serving.
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, from several brands (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, pan browned, 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 with 25% DV for vitamin B12 | 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 [22]. Foods providing 20% or more of the DV are considered high sources of a nutrient.
For a comprehensive list of foods high in B12, the USDA’s FoodData Central [21] is an excellent resource, offering detailed nutrient content for numerous foods.
Vitamin B12 Supplements and Medications
For individuals who struggle to obtain sufficient vitamin B12 from foods high in B12 alone or have conditions that impair absorption, supplements and prescription medications are available.
Dietary Supplements
Vitamin B12 supplements come in various forms:
- Multivitamins: Typically contain lower doses of vitamin B12, ranging from 5 to 25 mcg [23].
- B-Complex Supplements: Contain vitamin B12 along with other B vitamins, usually in doses of 50–500 mcg [23].
- Vitamin B12-Only Supplements: Offer higher doses, typically 500–1,000 mcg [23].
Cyanocobalamin is the most common form in supplements [1, 3, 23, 24], but adenosylcobalamin, methylcobalamin, and hydroxycobalamin are also available [23]. Absorption rates are similar across these forms, about 50% for doses under 1–2 mcg and significantly lower for higher doses [24, 25]. For instance, absorption is around 2% at 500 mcg and 1.3% at 1,000 mcg [25].
Sublingual vitamin B12 supplements (tablets or lozenges) are also available, but evidence suggests no significant difference in efficacy compared to oral forms [26, 27].
Prescription Medications
Prescription vitamin B12 medications, available as cyanocobalamin and hydroxycobalamin, are often administered parenterally via intramuscular injection [2]. This method is usually reserved for treating severe deficiency due to pernicious anemia or malabsorption conditions [5].
Nasal gel sprays are another prescription option, proving effective in raising vitamin B12 blood levels [28, 29]. Bioavailability of intranasal administration is about 2% for a 1,000 mcg dose, similar to oral doses [30].
Vitamin B12 Intake and Deficiency Prevalence
Most people in the United States consume adequate vitamin B12. NHANES data from 2017–March 2020 shows average daily intakes from foods high in B12 and beverages ranging from 3.66 mcg to 5.84 mcg, depending on age and sex [31]. Only a small percentage of the population has intakes below the EAR of 2 mcg [32].
However, vitamin B12 deficiency and insufficiency are still concerns. Approximately 3.6% of adults over 19 have vitamin B12 deficiency (serum B12 <200 pg/mL), and 12.5% have insufficiency (serum B12 <300 pg/mL) [34]. Older adults and pregnant women are more susceptible to lower vitamin B12 levels [34, 35].
Causes and Effects of Vitamin B12 Deficiency
Vitamin B12 deficiency can stem from several factors:
- Malabsorption: Difficulty absorbing B12 from foods high in B12 due to conditions like atrophic gastritis or gastrointestinal disorders.
- Lack of Intrinsic Factor: Pernicious anemia leads to a lack of intrinsic factor, crucial for B12 absorption.
- Gastrointestinal Surgery: Procedures affecting the stomach or small intestine can impair B12 absorption.
- Medications: Long-term use of metformin or proton pump inhibitors can interfere with B12 absorption.
- Dietary Deficiency: Insufficient intake of foods high in B12, particularly in vegan diets without supplementation.
Image alt text: An assortment of food items abundant in vitamin B12, such as beef steak, salmon fillet, a glass of milk, and eggs, illustrating diverse dietary sources.
Vitamin B12 deficiency can manifest in various symptoms:
- Megaloblastic Anemia: Characterized by large, abnormal red blood cells.
- Low Blood Cell Counts: Reduced white and red blood cells, platelets.
- Glossitis: Inflammation of the tongue.
- Fatigue and Palpitations: General weakness and heart palpitations.
- Pale Skin: Loss of skin color.
- Neurological Changes: Numbness, tingling in hands and feet, dementia.
- Infertility and Developmental Issues: Potential complications in severe cases.
Neurological symptoms can occur even without anemia, making early diagnosis crucial [36]. Untreated deficiency can lead to irreversible neurological damage.
While severe vitamin B12 deficiency is uncommon, low or marginal status (200–300 pg/mL) is more prevalent, affecting up to 40% in Western populations, especially those with low intake of foods high in B12 [9, 11].
Treatment typically involves vitamin B12 injections to bypass absorption issues. However, high doses of oral vitamin B12 can also be effective in normalizing serum levels [42].
Groups at Increased Risk of Vitamin B12 Deficiency
Certain populations are more vulnerable to vitamin B12 deficiency:
Older Adults
Between 3% and 43% of older adults, particularly those with atrophic gastritis, may have vitamin B12 deficiency [43, 44]. Conditions like pernicious anemia, atrophic gastritis, and Helicobacter pylori infection contribute to this risk [45, 46, 47].
Individuals with Pernicious Anemia
Pernicious anemia, an autoimmune disease, is a leading cause of severe vitamin B12 deficiency. It impairs intrinsic factor production, hindering B12 absorption [1, 48].
Individuals with Gastrointestinal Disorders
Conditions like celiac disease and Crohn’s disease can impair vitamin B12 absorption from foods high in B12 [2, 3, 49].
Individuals Post-Gastrointestinal Surgery
Surgeries like bariatric surgery can reduce cells producing hydrochloric acid and intrinsic factor, leading to B12 malabsorption [54, 55].
Vegetarians and Vegans
Vegetarians, especially vegans who avoid all animal products, are at higher risk due to the limited natural plant-based sources of vitamin B12. Fortified foods high in B12 and supplements are crucial for these groups [3, 57].
Infants of Vegan Mothers
Infants exclusively breastfed by vegan mothers can have very limited B12 reserves, leading to severe deficiency early in life. Maternal B12 status significantly impacts infant health [58, 59].
Vitamin B12 and Specific Health Conditions
Vitamin B12’s role in various health conditions is under ongoing research.
Cancer
The relationship between vitamin B12 and cancer risk is complex and not fully understood. Some studies suggest higher B12 levels might be linked to increased cancer risk [60, 62], while others indicate no association or even a protective effect [65, 71]. More research is needed to clarify these links [72, 73].
Cardiovascular Disease and Stroke
While vitamin B12 plays a role in homocysteine metabolism, and elevated homocysteine is linked to CVD, studies have not consistently shown that vitamin B12 supplementation reduces CVD risk [76, 77, 78]. Supplementation lowers homocysteine levels but doesn’t definitively prevent heart attacks or reduce CVD-related deaths [78, 79].
Dementia and Cognitive Function
Low vitamin B12 levels have been associated with poor cognitive function and a higher risk of dementia in observational studies [84, 85]. However, clinical trials generally have not shown that vitamin B12 supplementation improves cognitive function or reduces dementia risk, even though it can lower homocysteine levels [95, 97]. Further research is necessary to understand the role of vitamin B12 in cognitive health [98].
Energy and Endurance
Despite being promoted as an energy booster, vitamin B12 supplementation does not enhance energy or athletic performance in individuals without a deficiency [99, 100]. Its benefits are primarily for correcting deficiencies, not for boosting energy in healthy individuals.
Safety and Health Risks of Excessive Vitamin B12 Intake
Vitamin B12 is considered to have low toxicity, and the FNB has not established a UL due to its safety profile [1]. The body does not store excess vitamin B12, and even high doses are generally safe.
Interactions with Medications
Vitamin B12 can interact with certain medications, and some medications can affect vitamin B12 levels:
Gastric Acid Inhibitors
Proton pump inhibitors (e.g., omeprazole) and histamine 2-receptor antagonists (e.g., cimetidine) can reduce vitamin B12 absorption from foods high in B12 by decreasing gastric acid production [101, 102, 103].
Metformin
Metformin, used for diabetes management, may decrease vitamin B12 absorption and serum levels [103].
Individuals taking these medications should consult their healthcare providers about monitoring their vitamin B12 status.
Vitamin B12 and Balanced Diets
The 2020–2025 Dietary Guidelines for Americans emphasizes obtaining nutrients primarily from food. Foods high in B12, particularly from animal sources and fortified foods, play a crucial role in meeting vitamin B12 needs as part of a healthful dietary pattern.
A balanced diet rich in various food groups ensures adequate vitamin B12 intake:
- Include diverse vegetables, fruits, and whole grains.
- Consume fat-free or low-fat dairy products, good sources of vitamin B12.
- Incorporate protein foods such as lean meats, poultry, fish, eggs, and plant-based proteins. Fish and red meat are excellent foods high in B12.
- Limit added sugars, saturated fats, sodium, and alcohol.
Image alt text: A visually appealing table arrangement showcasing diverse food groups as per the Dietary Guidelines for Americans, including fruits, vegetables, grains, dairy, and proteins, emphasizing a balanced dietary approach.
For more information on building a healthy dietary pattern, refer to the Dietary Guidelines for Americans and USDA’s MyPlate.
References
[1] … (List of references as in the original document) …
Disclaimer
This fact sheet from the NIH Office of Dietary Supplements provides health information and should not replace medical advice. Consult with healthcare providers for personalized advice regarding dietary supplements and health.
Updated: March 26, 2024
