Folate Linked to Breast Cancer

Folate, also known as folic acid, helps convert vitamin B12 to one of it's coenzyme forms and helps synthesize the DNA required for all rapidly growing cells. The need for folate rises considerably during pregnancy and whenever cells are multiplying, so the recommendations for pregnant women are higher than for older adults. Women past their childbearing years, however, may have a higher risk of breast cancer with the use of supplements.
Researchers studied more than 1700 women in 1993 with high blood levels of folate. Ten years later, the women with the highest amount of blood folate levels were at a 70% higher risk of breast tumors that respond to estrogen or progesterone than those with the lowest levels. It is also believed that folate actually "feeds the tumor."
What to do? Until more studies are done, play it safe. If you take a multivitamin:

• Watch your cereals. Many breakfast/energy bars and cereals are fortified with folate or folic acid. If you typically eat more than one serving (about 1/2 - 1 cup) watch for cereals that contain 25 or 50% of the daily value for folic acid.
• Go whole grain. White pasta, rice, and breads are fortified with 100 to 130 mcg of folic acid per cup. Whole grain bread, pasta and brown rice are not.
• Don't worry about naturally occuring folate. The folate in orange juice, vegetables, beans and other foods isn't absorbed as well as the folic acid in fortified foods, so it's not a problem.

Just keep in mind than folate helps prevent spina bifida and neural-tube birth defects. So if you are, or could become pregnant, get at least 400 mcg a day of folic acid from a multivitamin or your food.
~ American Journal of Clinical Nutrition~