Why too much vitamin B9 might hurt babies
Adverse Effects of Excessive Folic Acid Consumption and Its Implications for Individuals With the Methylenetetrahydrofolate Reductase C677T Genotype
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Some moms have a gene that makes it hard to use the synthetic folic acid in pills and fortified foods. When they take too much, their bodies can’t process it all, and leftover folic acid might mess with brain development in babies.
Surprising Findings
High B12 levels, often considered protective, may increase autism risk when paired with high folic acid.
Public health messaging always promotes B12 as beneficial—this study flips the script by showing it can be part of the problem when combined with excess folic acid.
Practical Takeaways
If you're pregnant or planning to be, ask your doctor for a blood test to check your folate and B12 levels—and ask if you should switch from folic acid to 5-MTHF (methylfolate).
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Some moms have a gene that makes it hard to use the synthetic folic acid in pills and fortified foods. When they take too much, their bodies can’t process it all, and leftover folic acid might mess with brain development in babies.
Surprising Findings
High B12 levels, often considered protective, may increase autism risk when paired with high folic acid.
Public health messaging always promotes B12 as beneficial—this study flips the script by showing it can be part of the problem when combined with excess folic acid.
Practical Takeaways
If you're pregnant or planning to be, ask your doctor for a blood test to check your folate and B12 levels—and ask if you should switch from folic acid to 5-MTHF (methylfolate).
Publication
Journal
Cureus
Year
2025
Authors
J. Hecker, Rhett Layton, Robert W Parker
Related Content
Claims (6)
If you eat too much folic acid (a B vitamin found in supplements and fortified foods), it can hide the early blood signs that you're low on vitamin B12, so doctors might not catch the problem until your nerves are already damaged.
If your body has a hard time processing regular folic acid due to a common gene variation, taking 5-MTHF instead might help because your body can use it right away—without needing to convert it—and that could mean less leftover folic acid floating around, which might be safer.
In the U.S. and Canada, they added folic acid to foods like bread and cereal, and many women also take vitamins with folic acid—so now a lot of women are getting more than the safe upper limit, and doctors are worried this might cause hidden health problems.
Some women have a genetic variation that makes it harder for their body to turn regular folic acid (found in supplements and fortified foods) into the form it actually needs. This can cause extra folic acid to build up in the blood, which might mess with B12 levels, raise a harmful chemical called homocysteine, and possibly make depression or schizophrenia more likely.
Some people have a genetic variation that makes it hard for their body to turn the kind of folic acid in vitamins and fortified foods into the active form their body actually needs, which can leave them with not enough usable folate.