High folic acid intakes do not increase colorectal cancer risk

According to a new study from the American Cancer Society there is no evidence that dietary fortification or supplementation with folic acid increases colorectal cancer risk.

In the study, data from 56,011 women and 43,512 men (aged 50 to 74 years) participating in the Cancer Prevention Study II was analyzed (1). The data showed that folate intake from dietary sources ranged from 175 to 354 micrograms per day, while average folic acid intake from fortified foods, supplements, and/or multivitamins ranged from about 71 to 660 micrograms per day. In addition, over 2,000 participants had intake levels greater than the Tolerable Upper Intake Level (UL) of 1,000 micrograms of folic acid per day. An analysis of this data showed that neither high intakes of natural folate nor folic acid were associated with an increased risk of colorectal cancer. Moreover, total folate (from all sources) was associated with a 19 percent reduction in the risk of developing colorectal cancer.

The researchers commented that these results should allay fears that increased intake of folic acid – the synthetic form of folate – are linked to colorectal cancer risk. In the past, concerns that folic acid may increase the risk of colorectal cancer had been expressed by some scientists suggesting that folic acid, and not folate, may promote the formation of cancers under select circumstances in which a person may already have a pre-cancerous or cancerous tumor.

An overwhelming body of evidence links has linked folate deficiency in early pregnancy to increased risk of neural tube defects (NTD) in infants, which led in 1998 to the introduction of public health measures in the US and Canada, whereby all grain products are fortified with folic acid. Preliminary evidence indicates that the measure is having an effect with a reported 15 to 50 percent reduction in NTD incidence. A total of 51 countries now have some degree of mandatory fortification of flour with folic acid.

1. Stevens V. L. et al. High levels of folate, from supplements and fortification, are not associated with increased risk of colorectal cancer. Gastroenterology. 2011.