Vitamin B12 is a water-soluble nutrient involved in several essential body processes.
The ideal dose varies based on your age, lifestyle, and specific health situation.
This article looks at the evidence behind B12 dosage recommendations for different people and purposes.
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Why do you need vitamin B12?
Vitamin B12 is essential for proper red blood cell production, DNA formation, nerve function, and metabolism.
It also helps reduce levels of homocysteine, an amino acid linked to higher risk of heart disease, stroke, and cognitive decline when elevated.1
While B12 is commonly marketed for energy, supplements haven’t been shown to boost energy in people who aren’t deficient. In those who are deficient, however, correcting the deficiency can improve energy levels.
B12 is found mainly in animal products—meat, seafood, dairy, and eggs. It’s also added to fortified foods like cereals and plant-based milks.
Your body can store B12 for several years, so severe deficiency is uncommon. However, mild deficiency affects up to 26% of the general population and is more prevalent in certain groups.
Suggested read: 9 Signs and Symptoms of Vitamin B12 Deficiency
Factors that increase your risk of B12 deficiency include:
- Following a vegetarian or vegan diet
- Being over 50 years old
- Gastrointestinal conditions like Crohn’s disease or celiac disease
- Digestive surgery, such as weight loss surgery or bowel resection
- Taking metformin or acid-reducing medications
- Certain genetic mutations (MTHFR, MTRR, CBS)
- Regular alcohol consumption
If any of these apply to you, supplementation may help meet your needs.
Summary: Vitamin B12 supports red blood cell production, nerve function, and DNA synthesis. It’s found primarily in animal products. Certain groups are at higher risk of deficiency and may benefit from supplements.
Suggested dosages of vitamin B12
The recommended daily intake (RDI) for vitamin B12 is 2.4 mcg for adults over 14.
However, the right dose depends on your age, lifestyle, and individual circumstances.
One important consideration: B12 absorption from supplements is relatively low. Your body absorbs only about 10 mcg from a 500 mcg supplement, and absorption efficiency decreases as doses increase.2
Here’s what the research suggests for different groups.
Adults under 50
For healthy adults under 50, the recommended daily intake is 2.4 mcg.
Most people meet this through diet alone. Two eggs (1.2 mcg), 3 ounces of tuna (2.5 mcg), and 3 ounces of beef (1.4 mcg) would more than double your daily requirement.
If you have factors that affect B12 absorption or intake, supplementation may still be worthwhile.
Adults over 50
Older adults face a higher risk of B12 deficiency. While relatively few younger adults are deficient, research shows that up to 62% of adults over 65 have suboptimal B12 levels.
This happens because aging naturally reduces stomach acid and intrinsic factor production—both necessary for B12 absorption from food.
The National Academy of Medicine recommends that adults over 50 get most of their B12 from supplements and fortified foods rather than relying solely on dietary sources.
Research suggests that doses of 500–1,000 mcg daily can help normalize B12 levels in most older adults.2
Suggested read: Top 12 Foods High in Vitamin B12 for Optimal Health
Pregnant women
Pregnancy increases B12 requirements slightly. Low maternal B12 levels have been associated with birth defects and adverse pregnancy outcomes.3
A Cochrane systematic review found that B12 supplementation during pregnancy may reduce maternal deficiency and improve both maternal and infant B12 status, though effects on clinical outcomes need more research.3
The recommended daily intake during pregnancy is 2.6 mcg. Most prenatal vitamins contain B12, but check the label to confirm.
Breastfeeding women
B12 deficiency in breastfed infants can lead to developmental delays, irritability, and failure to thrive.4
The recommended daily intake for breastfeeding women is 2.8 mcg—slightly higher than during pregnancy.
Vegetarians and vegans
The recommended intake doesn’t change for plant-based diets, but meeting that requirement is significantly harder without animal products.
Studies show that a large proportion of vegetarians and vegans have low B12 levels. A systematic review found that children and adolescents on vegan or macrobiotic diets had significantly lower B12 levels than omnivores, though adequate total B12 intake nullified this difference.5
For vegans, some research suggests doses of up to 6 mcg daily, while others recommend higher doses to account for absorption limitations. A well-planned supplementation strategy is essential for anyone avoiding animal products.4
Suggested read: What Every Vegan Should Know About Vitamin B12
For improved energy
There’s no evidence that B12 supplements boost energy in people who aren’t deficient.
For those with confirmed deficiency, one approach is to take 1,000 mcg daily for a month, then switch to a maintenance dose of 125–250 mcg per day.
People with absorption issues (such as those with Crohn’s disease or after gastric surgery) may benefit from B12 injections, which bypass the digestive system entirely.
For memory and mood
B12 deficiency has been linked to cognitive issues, but evidence for supplements improving cognition in non-deficient people is limited.
A large meta-analysis found that B vitamin supplementation may slow cognitive decline, particularly with longer interventions (over 12 months) and in people without existing dementia.1
There are no specific dosage recommendations for cognitive benefits beyond ensuring adequate B12 status.
Summary: The general recommendation is 2.4 mcg daily for adults. Older adults may need 500–1,000 mcg to normalize levels. Pregnant and breastfeeding women need 2.6–2.8 mcg. Vegans require reliable supplementation.
Potential side effects of vitamin B12
Vitamin B12 is water-soluble, meaning excess amounts are excreted in urine. Because of its safety profile, no tolerable upper intake level has been established.
That said, some rare side effects have been reported:
- B12 injections may cause skin reactions like acne or dermatitis
- Very high doses (over 1,000 mcg) have been associated with complications in people with kidney disease
- Extremely high blood levels in pregnant women have been linked to increased autism risk in offspring in some studies
For most people, B12 supplementation is safe even at high doses. If you have kidney problems or are pregnant, discuss appropriate dosing with your healthcare provider.
Suggested read: How Much Vitamin B12 Is Too Much? Safe Dosage & Risks
Summary: B12 is generally safe with no established upper limit. Rare side effects may occur with injections or very high doses, particularly in people with kidney disease.
Summary
Vitamin B12 plays essential roles in nerve function, red blood cell production, and DNA synthesis.
The recommended daily intake ranges from 2.4 mcg for adults to 2.8 mcg for breastfeeding women. Most people meet these needs through diet, but older adults, vegans, and those with absorption issues often benefit from supplementation at higher doses.
B12 supplements are safe for most people, though those with specific health conditions should consult their doctor about appropriate dosing.
Wang Z, Zhu W, Xing Y, Jia J, Tang Y. B vitamins and prevention of cognitive decline and incident dementia: a systematic review and meta-analysis. Nutr Rev. 2022;80(4):931-949. PubMed ↩︎ ↩︎
Carmel R. Efficacy and safety of fortification and supplementation with vitamin B12: biochemical and physiological effects. Food Nutr Bull. 2008;29(2 Suppl):S177-87. PubMed ↩︎ ↩︎
Finkelstein JL, Fothergill A, Venkatramanan S, et al. Vitamin B12 supplementation during pregnancy for maternal and child health outcomes. Cochrane Database Syst Rev. 2024;1(1):CD013823. PubMed ↩︎ ↩︎
Müller P. Vegan Diet in Young Children. Nestle Nutr Inst Workshop Ser. 2020;93:103-110. PubMed ↩︎ ↩︎
Jensen CF. Vitamin B12 levels in children and adolescents on plant-based diets: a systematic review and meta-analysis. Nutr Rev. 2023;81(8):951-966. PubMed ↩︎
Sarah M.
Linda P.
Maya T.
Marcus J.
Emma R.
Amanda K.
Chris B.
David L.
James W.
Jennifer S.
Kevin H.
Lisa C.
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