Quick Answers
The recommended daily intake of vitamin B12 for adults is 2.4 mcg. Most multivitamins contain around 6 mcg vitamin B12 per serving. The common supplemental doses of vitamin B12 are between 25-100 mcg. High dose vitamin B12 supplements can contain up to 5000 mcg per serving.
What is Vitamin B12?
Vitamin B12, also known as cobalamin, is a water-soluble vitamin that plays essential roles in red blood cell formation, cell metabolism, nerve function and DNA synthesis and regulation. Vitamin B12 exists in a few different forms, including cyanocobalamin, methylcobalamin and adenosylcobalamin. In supplements and fortified foods, vitamin B12 is usually found as cyanocobalamin.
Vitamin B12 is naturally present in many animal-sourced foods like meat, fish, dairy products and eggs. It can also be found in fortified breakfast cereals and nutritional yeast. Vitamin B12 is not naturally present in plant foods, but some plant-based milk alternatives and vegetarian products are fortified with it.
In the body, vitamin B12 acts as a cofactor and coenzyme to metabolize and synthesize DNA, form red blood cells and maintain healthy nerve cells. Adequate vitamin B12 levels are crucial to neurological function, DNA regulation, cardiovascular health and energy levels.
Daily Recommended Intake
The recommended daily allowance (RDA) for vitamin B12 is:
- Infants 0–6 months: 0.4 mcg
- Infants 7–12 months: 0.5 mcg
- 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: 2.4 mcg
- Pregnant women: 2.6 mcg
- Breastfeeding women: 2.8 mcg
The upper limit for vitamin B12 is not definitively established, but excessive intake above the RDA does not appear to cause harm or adverse effects in healthy individuals.
Sources of Vitamin B12
The best food sources of vitamin B12 include:
- Liver and organ meats
- Beef
- Salmon, tuna, cod and other fish
- Shellfish like clams, oysters and mussels
- Eggs and dairy products
- Fortified cereals
- Nutritional yeast
For those following plant-based diets, getting enough active vitamin B12 may be a challenge since it is not usually present in plant foods. However, some breakfast cereals, plant-based milk, vegetarian meat alternatives and nutritional yeast are fortified with vitamin B12.
Vitamin B12 in Supplements
Most standard multivitamins contain between 6-25 mcg vitamin B12 per serving, which is well above the RDA. Vitamin B12 is also available as a standalone supplement, usually in higher doses ranging from 25 mcg to 5000 mcg per serving.
Some common supplemental doses of vitamin B12 include:
- 25 mcg – found in basic B-complex vitamins
- 50 mcg – common dose in most standard multivitamins
- 100 mcg – common dose in standalone B12 supplements
- 500 mcg – high dose capsules or sublingual tablets
- 1000-5000 mcg – very high dose sublingual or injectable B12
While there is no established upper limit for vitamin B12 intake, there is rarely a need to take more than 100-200 mcg per day unless treating a confirmed deficiency. Extremely high doses above 1000 mcg per day should only be taken under medical supervision.
Benefits of Vitamin B12 Supplements
Some key benefits of taking a vitamin B12 supplement in appropriate doses may include:
- Increasing energy levels
- Supporting neurological function
- Maintaining red blood cell and DNA production
- Elevating mood
- Aiding cognitive processes
- Promoting cardiovascular health
- Preventing anemia
- Boosting metabolism
- Treating vitamin B12 deficiency
For those following plant-based diets, taking a vitamin B12 supplement is especially important to prevent deficiency, since active B12 is not present in plant foods. Older adults and those with digestive conditions leading to poor absorption may also benefit from supplementing.
When to Take Vitamin B12
Vitamin B12 supplements are generally recommended to be taken once per day with a meal. This is because the gastric acid secreted during digestion helps release vitamin B12 from proteins in food or supplements.
Vitamin B12 is water-soluble and does not get stored in large amounts within the body. Taking it daily helps replenish levels consistently. For those with a diagnosed deficiency, a healthcare provider may recommend spreading out doses to several times a day.
Vitamin B12 Absorption
Vitamin B12 requires adequate stomach acid and a complex absorption process to be utilized by the body. When vitamin B12 in food or supplements reaches the stomach, it binds to a protein called R-protein or haptocorrin.
In a healthy individual, the acid environment of the stomach promotes the release of vitamin B12 from the protein. Vitamin B12 then attaches to another transport protein called intrinsic factor that takes it to the end of the small intestine to be absorbed into the bloodstream.
Certain conditions like atrophic gastritis, celiac disease, Crohn’s disease, surgery removing parts of the stomach, and long-term use of acid-reducing medications can impair the absorption of vitamin B12 from food and supplements. Those with absorption issues may require B12 shots or high dose supplements to prevent deficiency.
Toxicity and Side Effects
Vitamin B12 has extremely low toxicity and does not cause adverse effects in most people at doses up to 200 mcg per day. At very high supplemental doses of 1000 mcg per day and above, side effects like diarrhea, headache, anxiety, nausea, vomiting, and redness of the skin may occur.
However, there are no known toxic effects from high vitamin B12 intake by itself, even in doses up to 5000 mcg per day. Effects may be exacerbated when extremely high doses of B12 are paired with certain medications or supplements.
Special Considerations
Here are some special considerations when taking vitamin B12 supplements:
- Deficiency: Those with pernicious anemia, atrophic gastritis, celiac or Crohn’s disease are at risk of B12 deficiency and may require high dose supplements or injections.
- Sensitivities: People with cobalt allergies should avoid vitamin B12 supplements and eat B12-fortified foods instead.
- Interactions: Very high dose vitamin B12 could impact the efficacy of chloramphenicol antibiotics. Awareness of this interaction is advised.
- Time released: Vitamin B12 time released or extended release supplements may not be as well absorbed compared to regular capsules.
Who May Need Vitamin B12 Supplements
The following groups are more likely to require vitamin B12 supplementation:
- Vegans and vegetarians
- Older adults
- Those with gastrointestinal disorders, digestive issues or surgeries
- People taking metformin long-term
- Those with anemia, fatigue or energy issues
- Individuals with neurological symptoms
- People with mood disorders
- Those with a vitamin B12 deficiency
Vitamin B12 blood testing can confirm deficiency. Doctors may prescribe high dose supplements or B12 injections if levels are very low.
Signs of Vitamin B12 Deficiency
Some common symptoms of vitamin B12 deficiency include:
- Weakness and fatigue
- Tingling or numbness in hands and feet
- Difficulty thinking and confusion
- Memory issues
- Low mood or depression
- Vision disturbances
- Pale skin
- Smooth, sore tongue
- Fast heartbeat and shortness of breath
- Headaches and dizziness
Without treatment, vitamin B12 deficiency can potentially cause permanent nerve damage. Long-term severe deficiency has also been linked to a higher risk of dementia and mental decline in older adults.
Signs of Vitamin B12 Excess
Consuming vitamin B12 from food sources and in amounts up to 200 mcg per day is not associated with adverse effects in healthy people. However, taking vitamin B12 supplements in very high doses for long periods may lead to the following symptoms:
- Skin redness, rash or itching
- Acne or dermatitis
- Digestive discomfort like nausea or diarrhea
- Headache and lightheadedness
- Anxiety or nervousness
- Rapid or irregular heartbeat
- Sleep issues like insomnia
- Tingling sensation in the limbs
These effects appear to be transient and resolve when high dose supplementation is stopped. But it is best to keep vitamin B12 intake within recommended upper limits unless directed to take high doses for a deficiency.
Conclusion
The daily recommended intake of vitamin B12 for adults is 2.4 mcg, though no toxicity has been observed at doses up to 200 mcg. Many supplements provide 25-100 mcg vitamin B12 per serving, which is sufficient to meet needs without going above the upper limit.
Those following plant-based diets, with digestive disorders, older adults and individuals with neurological symptoms are more likely to benefit from vitamin B12 supplementation. Doses between 25-100 mcg per day taken with food are adequate for most people.
Very high dose B12 supplements above 1000 mcg per day should only be taken under medical supervision to treat a confirmed vitamin B12 deficiency. Monitoring for potential side effects like skin redness, digestive issues and headaches is advised at these super-high doses.
