You might want to ask your doctor why it was prescribed but here is some information that may explain it a little better.

"Folic acid is used to treat or prevent folic acid deficiency. It is a B-complex vitamin needed by the body to manufacture red blood cells. A deficiency of this vitamin causes certain types of anemia (low red blood cell count)." -- Folic Acid: https://medlineplus.gov/druginfo/meds/a682591.html