In 1998 the Food and Drug Administration mandated that certain foods be fortified with folic acid because it had been shown that folic acid supplementation for pregnant mothers, significantly reduced neural tube defects in babies (e.g. spina bifida).
A study at the Washington University in St. Louis suggests that this fortification may also have lead to lower cases of some cancers in the infants. To quote:
“Rates of Wilms tumor (WT), primitive neuroectodermal tumors (PNETs), and ependymomas were significantly lower postfortification”
Read more here.