For years, doctors have been ordering expectant mothers to consume plenty of folic acid, since it can help prevent some birth defects. However, recent studies hint that we should all boost our intake of this critical B vitamin.

For example, researchers at New York's Albert Einstein College of Medicine looked at the diets of more than 55,000 women and found that those who took in 400 micrograms of folate (the food form of folic acid) each day cut their risk of colon cancer by 40 percent. In a similar study by a team at Harvard University, the same amount of folic acid appeared to reduce by half the likelihood that a woman with a family history of colon cancer would develop the disease.

Folic acid protects the DNA in cells from cancer-causing substances, which may explain why the vitamin seems to stop tumors from forming in the colon. Likewise, researchers at the National Institutes of Health (NIH) have produced the first solid evidence that diets low in folic acid may harm brain cells. Lab mice fed folate-poor diets suffered damage to neurons by a naturally occurring substance called homocysteine, says Dr. Mark Mattson of the NIH. As the rodents were exposed to higher levels of homocysteine, they began to develop problems similar to those experienced by patients with Alzheimer's and Parkinson's diseases.

Leafy greens, beans, and orange juice are good sources of folate. Most bread, pasta, and other grains are enriched with folic acid, too, and a multivitamin supplies a day's worth of this critical nutrient.