Folate is essential for normal cell growth. However, in animal models that already had pre-cancerous or cancerous lesions, folic acid made the cancers worse. In this study, researchers looked at the effects of high dose folic acid (100ng/ml) on colon cancer cells. They found that the cancer cells grew faster and had higher metabolic activity. They also found that folate seemed to lower iron metabolism and therefore lower the iron levels in the cells.
Ironically, folate has been used clinically in high doses to treat cervical dysplasia. We don’t yet know why megadoses seem to be good for treating some precancerous lesions and for promoting others.
So the bottom line is its probably not a good idea to supplement with high doses of folic acid unless you have a very good reason to do so.
Br J Nutr. 2007 Sep 10;:1-6 [Epub ahead of print]
High folic acid increases cell turnover and lowers differentiation and iron content in human HT29 colon cancer cells. Pellis L, et al.