Women of childbearing age aren't getting enough of the B vitamin folate, according to the Centers for Disease Control and Prevention. This is a concern because the dramatic decline in neural tube birth defects in the late 1990s resulted directly from a U.S. mandate to fortify cereals and flours with folic acid, the synthetic version of folate. Why levels are dropping is unknown. Possible culprits include the recent low-carb craze, during which women avoided grains and cereals, and the growing popularity of whole grains, whose trace amounts of folate exempt them from the mandate. To ensure you get the necessary 400 micrograms daily, take folic acid supplements and eat folate-rich foods like spinach or beans, as well as enriched cereals.