Folic acid helps the body build and maintain DNA and is important in helping the body make new cells, especially red blood cells. [American Cancer Institute, 2011]
Vitamin B9 can either be called a "folate" or "folic acid", both are often used interchangeably, although they are slightly different. Foliate is the proper name for it when taken in food. Folic Acid is the proper term when taken as a vitamin as either a tablet or powder form.
Low levels of folic acid in the blood have been linked with higher rates of colorectal cancer and some other types of cancer, as well as with certain birth defects. It is not clear whether consuming recommended (or higher) amounts of folic acid-from foods or in supplements can lower cancer risk in some people. These issues are being studied. [American Cancer Institute, 2011]
How folic acid might affect cancer risk is not exactly clear. Cells need folic acid to make and repair DNA when they divide to create new cells, and it. Folic acid may be involved in how cells turn certain genes on and off. Scientists believe low levels of folic acid can lead to changes in the chemicals that affect DNA, which may alter how well cells can repair themselves or divide without making mistakes. These changes might in turn lead to cancer. Further research is needed.[American Cancer Institute, 2011]
Whether folic acid works against cancer may also depend on when it is taken. Some researchers think that folic acid may not be helpful, and could even be harmful, in people who already have cancer or pre-cancerous conditions. For example, two randomized, controlled trials found that folic acid supplements had no effect on women who already had pre-cancerous conditions of the cervix. Along those same lines, drugs that block folic acid are routinely used to treat cancer. This seems contradictory, but folic acid is used to make DNA and RNA. [American Cancer Institute, 2011]
High doses of folic acid can interfere with the action of some chemotherapy drugs, such as Methotrexate. [American Cancer Institute, 2011] Interactions specifically with high levels of Citrus Fruits are also an issue with Rapamycin treatments including; Everolimus (Afinitor) more commonly known as RAD001, as well as with Sirolimus.
Folic acid can also mask symptoms of vitamin B12 deficiency by correcting the anemia caused by low vitamin B12 levels. But vitamin B12 deficiency can still cause nervous system damage, which folic acid cannot correct. In fact, high doses of folic acid can worsen the nervous system damage, and continued B12 deficiency can allow the damage to become permanent. [American Cancer Institute, 2011]