Vitamin B12 levels and autism risk in children
What it found
Studies in people give mixed results on whether low or high vitamin B12 levels in mothers and children are linked to autism.
Some studies find a link, others find none.
What they found
Studies in people
Maternal B12 and autism
One large study of 1558 children with autism and 1558 controls found no overall link between mothers' vitamin B12 levels and autism risk. But both high levels (at or above the 81st percentile) and low levels (below the 20th percentile) in the first trimester were linked to higher risk of childhood autism.
High B12 and autism risk
A study found that mothers with vitamin B12 levels above 536.8 pmol/L at birth had a 2.5 times higher risk of having a child with autism. Levels above 600 pmol/L were linked to a 3 times higher risk.
B12 supplementation in pregnancy
Two randomized trials of vitamin B12 supplementation during pregnancy gave unclear results. One found no difference in infant development at 9 months, while the other found better expressive language at 30 months in children of supplemented mothers.
B12 levels in children with autism
Some studies found lower vitamin B12 levels in children with autism compared to typically developing children, and these lower levels were linked to more severe symptoms. Other studies found no difference.
B12 supplementation in children
A meta-analysis found that vitamin B12 supplementation improved methylation and glutathione levels, which were linked to improvements in autism symptoms like communication and daily functioning. Side effects like hyperactivity and sleep problems were few and mild, and similar to placebo.
Animal and lab studies
Gut bacteria and B12 in animals
In nematodes and rats, vitamin B12 produced by gut bacteria or given as a supplement reduced autism-like behaviors and oxidative stress. These effects were not seen with bacteria that do not produce B12.
What the authors conclude
“Due to the inconsistency of the results obtained, additional studies, such as longitudinal studies, are required to determine whether there is a causal relationship between vitamin B12 levels and the severity of ASD symptoms, which will allow for monitoring changes over a longer period of time.”
Also in their conclusions
- They conclude that vitamin B12 may be one of the risk factors for autism, but that the link remains inconclusive due to inconsistent findings.
- They advise that more longitudinal studies are needed to determine whether there is a causal relationship between vitamin B12 levels and the severity of autism symptoms.
- They suggest that identifying specific biochemical markers could help select children most likely to benefit from vitamin B12 supplementation.
How it was done
The authors wanted to examine the latest research on how vitamin B12 deficiency and excess might relate to the risk and development of autism spectrum disorder, and to identify directions for future research.
They reviewed studies published between 2000 and 2024 on vitamin B12, autism, gut bacteria, neurodevelopment, and related topics. They included original research and reviews, excluding conference abstracts and non-English papers.
What it can’t tell you
- Many of the studies in people were observational, so they can show a link but not prove that vitamin B12 levels cause autism.
- Animal and lab studies cannot show what happens in people.
- Single-point measurements of vitamin B12 cannot account for changes over time or other factors like diet and environment.
Who paid
- Funding
- Funded by Medical University of Białystok (from the PubMed record).
- Conflicts
- The authors declare no conflicts of interest.
- Authors work at
- Medical University of Bialystok, Poland
The paper
- Title
- Vitamin B12 and Autism Spectrum Disorder: A Review of Current Evidence
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Zwierz M, Suprunowicz M, Mrozek K, et al (2025). Vitamin B12 and Autism Spectrum Disorder: A Review of Current Evidence. Nutrients. doi:10.3390/nu17071220Free full textPubMed 40218978DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error