Quick answer
NIH sets no upper limit for vitamin B12 and says it has not been shown to cause harm. A 2026 Cochrane review of 16 trials in 4,083 children under 12 found little to no difference in adverse effects, though few trials reported them. Ask a pediatrician before giving a child or teen a B12 supplement.1,2
Key facts
- NIH says vitamin B12 has not been shown to cause any harm, even at high doses, and sets no upper limit.1,3
- A 2026 Cochrane review pooled 16 trials with 4,083 children under 12, using 0.9 to 150 mcg a day for 28 days to 31 months.2
- In the one trial that compared adverse effects, 9.2% of children with B12 and 5.9% without had one, a difference the review called little to none at low certainty.2
- The review found little or no effect on growth, attention, development or anemia, and lower rates of B12 deficiency.2
- NIH's survey data show 28% of children aged 2 to 5 and 9% of those aged 12 to 19 used a supplement containing B12.3
What does NIH say about vitamin B12 for children and teens?
NIH lists recommended intakes of B12 by age, rising from early childhood through the teen years, and sets no upper limit for any age because the vitamin has a low potential for harm. The consumer sheet says B12 has not been shown to cause any harm even at high doses, and the professional sheet explains the body does not store the excess.1,3
The professional sheet also reports how common supplements are: in a national survey, 28% of children aged 2 to 5 and 9% of those aged 12 to 19 used a supplement with B12, and children and teens who took supplements averaged between 24.7 and 47.4 mcg a day from food, drinks and supplements together.3
Neither sheet gives a different caution for children from the one it gives for adults, and neither describes harm in children. That is a statement about what the sheets contain, not a finding that no one has been affected.1,3
What did the Cochrane review of children find?
The 2026 Cochrane review is the main trial summary for oral B12 in children. It pooled 16 randomized trials with 4,083 children under 12 in ten countries, with follow-up from 5 weeks to 31 months. Supplements of B12 alone, or with other micronutrients, were compared with placebo or no supplement. The review left out trials in pregnant or breastfeeding women and trials that gave B12 by injection.2
| Outcome | What the review found | Certainty |
|---|---|---|
| B12 deficiency | Lower with B12: 1.8% versus 7.6% (3 trials, 642 children) | High |
| Growth in height | Little to no difference | Low |
| Attention and thinking | Little to no difference | Low |
| Anemia | Little to no difference (9.1% versus 4.5%; 2 trials, 144 children) | Low |
| Any adverse effects | Little to no difference (9.2% versus 5.9%; 1 trial, 574 children) | Low |
The authors added that few studies reported growth, cognition, development, anemia or adverse effects at all, and that no trial of B12 alone reported the occurrence of any adverse effect. That gap limits what can be said about safety.2
What does the label of a B12 injection say about children?
The label of a vitamin B12 injection has a pediatric section that says intake in children should be the amount the Food and Nutrition Board recommends. It also warns that the injection contains benzyl alcohol, which has been associated with a fatal gasping syndrome in premature infants. Both points concern a prescription injection and not an oral supplement.4
What about kids with autism or ADHD?
The Cochrane review looked at growth, thinking skills, development, anemia and B12 levels in children. It did not look at autism or ADHD, and it excluded injections. NIH's fact sheets for B12 do not recommend it for either condition, so the sources checked give no basis for saying it helps or harms those children. Parents who are considering B12 for a condition should ask the child's doctor.1,2
Who should ask a doctor before a child or teen takes vitamin B12?
- A pediatrician, before giving a B12 supplement to a child.1
- A doctor, for a child or teen who eats no animal foods, since NIH says B12 occurs naturally only in animal foods.1,3
- A doctor or pharmacist, for a teen who takes metformin or a proton pump inhibitor, which can lower B12 levels.3
- A doctor, for any child with numbness, tingling, poor growth or developmental delay, which need testing and not self-treatment.3
Questions people ask
Is vitamin B12 safe for kids?
NIH sets no upper limit for B12 and says it has not been shown to cause harm, and a 2026 Cochrane review of 16 trials found little to no difference in adverse effects, though few trials reported them. Ask a pediatrician.1,2
Is vitamin B12 good for teens?
NIH lists a recommended intake for teens aged 14 to 18 and sets no upper limit. The sources checked do not report trial results on supplements in healthy teens. Ask a doctor about your own reason for taking one.1,3
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Sources
- National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Consumers. Updated December 15, 2023. Opened 2026-10-07.
- Larvie DY, Guitron Leal CE, Venkatramanan S, Palma Molina XE, Steel LB, Kuriyan R, Finkelstein JL. Vitamin B12 supplementation for growth, development, and cognition in children (Cochrane systematic review of 16 randomized trials). Cochrane Database Syst Rev. 2026;6:CD015264. Opened 2026-10-11.
- National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. Updated July 2, 2025. Opened 2026-10-07.
- Cyanocobalamin injection, USP: prescribing information (Hikma Pharmaceuticals USA). DailyMed, U.S. National Library of Medicine. Published May 11, 2026. Opened 2026-10-11.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.