Vitamin B9 (folate / folic acid)

Folate (vitamin B9) is essential for DNA synthesis and red-blood-cell production. Its best-established supplemental use is before and during early pregnancy, where folic acid clearly lowers the risk of neural-tube defects: one of the strongest cases for any supplement.

For general use, folate works hand in hand with vitamin B12, and supplementing folate can mask a B12 deficiency, so the two are checked together. Active forms (methylfolate, folinic acid) are options for people with certain MTHFR variants, though for most, folic acid is effective.

Sources

• PubMed: folate folic acid supplementation neural tube defect pregnancy (research overview)