You may not realize it, but your body is constantly making new cells to replace old ones that wear out. Your red blood cells are a good example—every day, you make millions of new ones to replace old ones that are too beat up to work well anymore. All those new cells are why you need a good supply of folic acid. Without it, you can't make enough new cells fast enough or well enough.
And folic acid is especially important for cells that wear out and divide rapidly, such as red blood cells, skin cells, and the cells that line your small intestine. What it all comes down to is that you need folic acid for the normal growth and maintenance of every cell in your body.
Folic acid does some other amazing things for your health. In the past few years we've learned that folic acid prevents birth defects, helps prevent heart disease, and may even help prevent cancer. The evidence is so convincing that starting in 1998 many common foods, including bread, breakfast cereal, pasta, and rice, will have extra folic acid, by order of the FDA.