[A two-faced vitamin : Folic acid - prevention or promotion of colon cancer?]

In the late 1930s, it was discovered that liver and yeast extracts can be used to correct certain cases of megaloblastic anemia in pregnancy. The factor responsible for this was isolated from spinach leaves in the 1940s, and referred to as folate, a term derived from the Latin word folium for leaf. Folate is considered an essential nutrient for human beings. Folic acid, the synthetic form of the vitamin, is used in dietary supplements, medicines and fortified foods. Since the 1980s, it has been recommended that women who plan to become pregnant and pregnant women during the first trimester of pregnancy take folic acid supplements. This recommendation was based on studies that revealed that periconceptional folic acid supplementation can reduce the risk for neural tube defects (NTDs). Many countries later implemented folic acid fortification programs. The resulting population-wide increase of folic acid intakes led to significant reductions in NTD rates. However, a temporarily increased colorectal cancer incidence has been reported to coincide with the fortification programs in the USA and Canada. On the basis of currently available data from experimental and human studies it can be concluded that the association between folate/folic acid and cancer is rather complex: Folate intake in the range of the dietary reference intake (DRI) is associated with a reduced risk for cancer in healthy populations, whereas high intakes of folic acid might result in an increased risk for cancer incidence or progression in persons with precancerous lesions and under certain conditions. Since no adverse effects have been observed in association with the intake of dietary folate, research activities that aim at investigating cause and effect relationships focus on folic acid.