Mandatory fortification with folic acid aims to increase intake of folate in women during early pregnancy and to reduce neural tube defects in their babies. The case for mandatory fortification is strengthened by the purported association of increased intake of folate with reduced incidence of cancer, thus benefiting the whole population. But new data suggest that folate supplements may paradoxically have cancer promoting effects, enhancing the development and progression of undiagnosed premalignant and malignant lesions.

Folate metabolism is complex and influences several crucial pathways, including DNA synthesis and methylation, aberrations of which play a major role in carcinogenesis. Altered folate metabolism may disrupt these processes, providing mechanisms through which both folate deficiency and supplementation could influence cancer risk. This relation may be further complicated by using synthetic folic acid in supplements and fortification: its effects on folate metabolism are not identical to those of natural folates.1

Epidemiological studies have found that high folate intake is associated …