Folate is a generic term for a group of water soluble vitamin B compound that are required as coenzymes in a number of important methylation reactions. Colorectal cancer has been shown to be inversely associated with folate intake in observational studies, although some controversy still surrounds this relationship. Biochemically, folate is involved in the prevention of cancer because it is required for methylation repair or synthesis of DNA. The fortification of grain products in the United States of America with folic acid, a folate compound, gave researchers a unique opportunity to analyse the effect of dietary folate compounds on various disease states. The fortification of grain products in the United States was designed to decrease neural tube defects in new born infants, something that was shown to occur in the post-fortification (1997 to present) period.
Researchers1 have examined the association between folate intake and colorectal cancer risk using data from the National Institute of Health AARP diet and health study, which included a national cohort of 525,488 subjects aged 50-71 years. Dietary folate intake was calculated using a baseline food frequency questionnaires for the pre- and post-fortification period. Follow-up of the subjects occurred for 8.5 years following the fortification date, and during this time there were 7212 cases of cancer identified. In the post-fortification analysis a higher total dietary folate intake (≥900 versus <200µg/d) was associated with a lower risk of colorectal cancer (hazard ratio 0.7). The results showed that both supplements and dietary sources of folate were protective. In addition, similar associations existed for the pre-fortification period. Mean pre-fortification folate intake was 297µg/d, whereas mean post-fortification folate intake was 391µg/d.
Some studies have suggested that high levels of folate may actually increase rates of colorectal cancer, but no such association was shown in this study. In fact, increasing folate intake was linearly inversely associated with colorectal cancer risk, something that has been reported in other prospective studies. Supplemental folate in this study was reported as occurring exclusively from multivitamin use, and other studies have shown long term use of multivitamins containing ≥400 µg/d of folate are associated with reduced cancer risk in women. A plateau of folate intake likely exist, beyond which no further protection is evident, and so increasing intakes above this point may not be beneficial. Studies have shown that synthetic folate compounds in supplements are better absorbed than folate from food, although folate is widespread in foods and high intakes are possible through the diet.
RdB
