Folic acid is in everything from leafy greens and fruits to dried beans and nuts. Unfortunately arsenic is in a lot of things, too — including our drinking water. But taking a folic-acid supplement or eating folate-rich foods may help lessen the impact of arsenic exposure. A recent study published in the American Journal of Clinical Nutrition researched the supplement's effects on 200 folate-deficient Bangladeshis, in whose country arsenic exposure is a severe problem. Taking a supplement with 400 mcg for 12 weeks helped reduce their blood arsenic levels by more than 13 percent.

Arsenic, a chemical element used in insecticides and for pressure treating wood, makes its way into drinking water as arsenic-laced soil dissolves in ground water. (It also exists naturally in ground water.) In 2006, the EPA raised the amount of allowable arsenic in drinking water to 10 parts per billion. Even this seemingly small amount of exposure, however, has been linked to different types of cancer, cardiovascular disease, diabetes, and skin problems.

“Although our food supply is fortified with folate, there are regions such as New Hampshire, Maine, and parts of the South-west where arsenic exposure is a problem,” says Mary Gamble, PhD, lead author of the study and a professor at Columbia University. No matter where you reside, taking a folic-acid supplement “can't hurt,” even if you're not folate deficient, she says.